1 /*
   2  * Copyright (c) 2013, 2020, Oracle and/or its affiliates. All rights reserved.
   3  * Copyright (c) 2019, Azul Systems, Inc. All rights reserved.
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This code is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License version 2 only, as
   8  * published by the Free Software Foundation.  Oracle designates this
   9  * particular file as subject to the "Classpath" exception as provided
  10  * by Oracle in the LICENSE file that accompanied this code.
  11  *
  12  * This code is distributed in the hope that it will be useful, but WITHOUT
  13  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  14  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  15  * version 2 for more details (a copy is included in the LICENSE file that
  16  * accompanied this code).
  17  *
  18  * You should have received a copy of the GNU General Public License version
  19  * 2 along with this work; if not, write to the Free Software Foundation,
  20  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  21  *
  22  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  23  * or visit www.oracle.com if you need additional information or have any
  24  * questions.
  25  */
  26 
  27 package java.lang;
  28 
  29 import java.io.InputStream;
  30 import java.io.IOException;
  31 import java.io.UncheckedIOException;
  32 import java.io.File;
  33 import java.lang.reflect.Constructor;
  34 import java.lang.reflect.InvocationTargetException;
  35 import java.net.URL;
  36 import java.security.AccessController;
  37 import java.security.AccessControlContext;
  38 import java.security.CodeSource;
  39 import java.security.PrivilegedAction;
  40 import java.security.ProtectionDomain;
  41 import java.security.cert.Certificate;
  42 import java.util.ArrayList;
  43 import java.util.Collections;
  44 import java.util.Enumeration;
  45 import java.util.HashMap;
  46 import java.util.HashSet;
  47 import java.util.Map;
  48 import java.util.NoSuchElementException;
  49 import java.util.Objects;
  50 import java.util.Set;
  51 import java.util.Spliterator;
  52 import java.util.Spliterators;
  53 import java.util.WeakHashMap;
  54 import java.util.concurrent.ConcurrentHashMap;
  55 import java.util.function.Supplier;
  56 import java.util.stream.Stream;
  57 import java.util.stream.StreamSupport;
  58 
  59 import jdk.internal.loader.BootLoader;
  60 import jdk.internal.loader.BuiltinClassLoader;
  61 import jdk.internal.loader.ClassLoaders;
  62 import jdk.internal.loader.NativeLibrary;
  63 import jdk.internal.loader.NativeLibraries;
  64 import jdk.internal.perf.PerfCounter;
  65 import jdk.internal.misc.Unsafe;
  66 import jdk.internal.misc.VM;
  67 import jdk.internal.reflect.CallerSensitive;
  68 import jdk.internal.reflect.Reflection;
  69 import jdk.internal.util.StaticProperty;
  70 import sun.reflect.misc.ReflectUtil;
  71 import sun.security.util.SecurityConstants;
  72 
  73 /**
  74  * A class loader is an object that is responsible for loading classes. The
  75  * class {@code ClassLoader} is an abstract class.  Given the <a
  76  * href="#binary-name">binary name</a> of a class, a class loader should attempt to
  77  * locate or generate data that constitutes a definition for the class.  A
  78  * typical strategy is to transform the name into a file name and then read a
  79  * "class file" of that name from a file system.
  80  *
  81  * <p> Every {@link java.lang.Class Class} object contains a {@link
  82  * Class#getClassLoader() reference} to the {@code ClassLoader} that defined
  83  * it.
  84  *
  85  * <p> {@code Class} objects for array classes are not created by class
  86  * loaders, but are created automatically as required by the Java runtime.
  87  * The class loader for an array class, as returned by {@link
  88  * Class#getClassLoader()} is the same as the class loader for its element
  89  * type; if the element type is a primitive type, then the array class has no
  90  * class loader.
  91  *
  92  * <p> Applications implement subclasses of {@code ClassLoader} in order to
  93  * extend the manner in which the Java virtual machine dynamically loads
  94  * classes.
  95  *
  96  * <p> Class loaders may typically be used by security managers to indicate
  97  * security domains.
  98  *
  99  * <p> In addition to loading classes, a class loader is also responsible for
 100  * locating resources. A resource is some data (a "{@code .class}" file,
 101  * configuration data, or an image for example) that is identified with an
 102  * abstract '/'-separated path name. Resources are typically packaged with an
 103  * application or library so that they can be located by code in the
 104  * application or library. In some cases, the resources are included so that
 105  * they can be located by other libraries.
 106  *
 107  * <p> The {@code ClassLoader} class uses a delegation model to search for
 108  * classes and resources.  Each instance of {@code ClassLoader} has an
 109  * associated parent class loader. When requested to find a class or
 110  * resource, a {@code ClassLoader} instance will usually delegate the search
 111  * for the class or resource to its parent class loader before attempting to
 112  * find the class or resource itself.
 113  *
 114  * <p> Class loaders that support concurrent loading of classes are known as
 115  * <em>{@linkplain #isRegisteredAsParallelCapable() parallel capable}</em> class
 116  * loaders and are required to register themselves at their class initialization
 117  * time by invoking the {@link
 118  * #registerAsParallelCapable ClassLoader.registerAsParallelCapable}
 119  * method. Note that the {@code ClassLoader} class is registered as parallel
 120  * capable by default. However, its subclasses still need to register themselves
 121  * if they are parallel capable.
 122  * In environments in which the delegation model is not strictly
 123  * hierarchical, class loaders need to be parallel capable, otherwise class
 124  * loading can lead to deadlocks because the loader lock is held for the
 125  * duration of the class loading process (see {@link #loadClass
 126  * loadClass} methods).
 127  *
 128  * <h2> <a id="builtinLoaders">Run-time Built-in Class Loaders</a></h2>
 129  *
 130  * The Java run-time has the following built-in class loaders:
 131  *
 132  * <ul>
 133  * <li><p>Bootstrap class loader.
 134  *     It is the virtual machine's built-in class loader, typically represented
 135  *     as {@code null}, and does not have a parent.</li>
 136  * <li><p>{@linkplain #getPlatformClassLoader() Platform class loader}.
 137  *     All <em>platform classes</em> are visible to the platform class loader
 138  *     that can be used as the parent of a {@code ClassLoader} instance.
 139  *     Platform classes include Java SE platform APIs, their implementation
 140  *     classes and JDK-specific run-time classes that are defined by the
 141  *     platform class loader or its ancestors.
 142  *     <p> To allow for upgrading/overriding of modules defined to the platform
 143  *     class loader, and where upgraded modules read modules defined to class
 144  *     loaders other than the platform class loader and its ancestors, then
 145  *     the platform class loader may have to delegate to other class loaders,
 146  *     the application class loader for example.
 147  *     In other words, classes in named modules defined to class loaders
 148  *     other than the platform class loader and its ancestors may be visible
 149  *     to the platform class loader. </li>
 150  * <li><p>{@linkplain #getSystemClassLoader() System class loader}.
 151  *     It is also known as <em>application class loader</em> and is distinct
 152  *     from the platform class loader.
 153  *     The system class loader is typically used to define classes on the
 154  *     application class path, module path, and JDK-specific tools.
 155  *     The platform class loader is a parent or an ancestor of the system class
 156  *     loader that all platform classes are visible to it.</li>
 157  * </ul>
 158  *
 159  * <p> Normally, the Java virtual machine loads classes from the local file
 160  * system in a platform-dependent manner.
 161  * However, some classes may not originate from a file; they may originate
 162  * from other sources, such as the network, or they could be constructed by an
 163  * application.  The method {@link #defineClass(String, byte[], int, int)
 164  * defineClass} converts an array of bytes into an instance of class
 165  * {@code Class}. Instances of this newly defined class can be created using
 166  * {@link Class#newInstance Class.newInstance}.
 167  *
 168  * <p> The methods and constructors of objects created by a class loader may
 169  * reference other classes.  To determine the class(es) referred to, the Java
 170  * virtual machine invokes the {@link #loadClass loadClass} method of
 171  * the class loader that originally created the class.
 172  *
 173  * <p> For example, an application could create a network class loader to
 174  * download class files from a server.  Sample code might look like:
 175  *
 176  * <blockquote><pre>
 177  *   ClassLoader loader&nbsp;= new NetworkClassLoader(host,&nbsp;port);
 178  *   Object main&nbsp;= loader.loadClass("Main", true).newInstance();
 179  *       &nbsp;.&nbsp;.&nbsp;.
 180  * </pre></blockquote>
 181  *
 182  * <p> The network class loader subclass must define the methods {@link
 183  * #findClass findClass} and {@code loadClassData} to load a class
 184  * from the network.  Once it has downloaded the bytes that make up the class,
 185  * it should use the method {@link #defineClass defineClass} to
 186  * create a class instance.  A sample implementation is:
 187  *
 188  * <blockquote><pre>
 189  *     class NetworkClassLoader extends ClassLoader {
 190  *         String host;
 191  *         int port;
 192  *
 193  *         public Class findClass(String name) {
 194  *             byte[] b = loadClassData(name);
 195  *             return defineClass(name, b, 0, b.length);
 196  *         }
 197  *
 198  *         private byte[] loadClassData(String name) {
 199  *             // load the class data from the connection
 200  *             &nbsp;.&nbsp;.&nbsp;.
 201  *         }
 202  *     }
 203  * </pre></blockquote>
 204  *
 205  * <h3> <a id="binary-name">Binary names</a> </h3>
 206  *
 207  * <p> Any class name provided as a {@code String} parameter to methods in
 208  * {@code ClassLoader} must be a binary name as defined by
 209  * <cite>The Java&trade; Language Specification</cite>.
 210  *
 211  * <p> Examples of valid class names include:
 212  * <blockquote><pre>
 213  *   "java.lang.String"
 214  *   "javax.swing.JSpinner$DefaultEditor"
 215  *   "java.security.KeyStore$Builder$FileBuilder$1"
 216  *   "java.net.URLClassLoader$3$1"
 217  * </pre></blockquote>
 218  *
 219  * <p> Any package name provided as a {@code String} parameter to methods in
 220  * {@code ClassLoader} must be either the empty string (denoting an unnamed package)
 221  * or a fully qualified name as defined by
 222  * <cite>The Java&trade; Language Specification</cite>.
 223  *
 224  * @jls 6.7 Fully Qualified Names
 225  * @jls 13.1 The Form of a Binary
 226  * @see      #resolveClass(Class)
 227  * @since 1.0
 228  * @revised 9
 229  * @spec JPMS
 230  */
 231 public abstract class ClassLoader {
 232 
 233     private static native void registerNatives();
 234     static {
 235         registerNatives();
 236     }
 237 
 238     // The parent class loader for delegation
 239     // Note: VM hardcoded the offset of this field, thus all new fields
 240     // must be added *after* it.
 241     private final ClassLoader parent;
 242 
 243     // class loader name
 244     private final String name;
 245 
 246     // the unnamed module for this ClassLoader
 247     private final Module unnamedModule;
 248 
 249     // a string for exception message printing
 250     private final String nameAndId;
 251 
 252     /**
 253      * Encapsulates the set of parallel capable loader types.
 254      */
 255     private static class ParallelLoaders {
 256         private ParallelLoaders() {}
 257 
 258         // the set of parallel capable loader types
 259         private static final Set<Class<? extends ClassLoader>> loaderTypes =
 260             Collections.newSetFromMap(new WeakHashMap<>());
 261         static {
 262             synchronized (loaderTypes) { loaderTypes.add(ClassLoader.class); }
 263         }
 264 
 265         /**
 266          * Registers the given class loader type as parallel capable.
 267          * Returns {@code true} is successfully registered; {@code false} if
 268          * loader's super class is not registered.
 269          */
 270         static boolean register(Class<? extends ClassLoader> c) {
 271             synchronized (loaderTypes) {
 272                 if (loaderTypes.contains(c.getSuperclass())) {
 273                     // register the class loader as parallel capable
 274                     // if and only if all of its super classes are.
 275                     // Note: given current classloading sequence, if
 276                     // the immediate super class is parallel capable,
 277                     // all the super classes higher up must be too.
 278                     loaderTypes.add(c);
 279                     return true;
 280                 } else {
 281                     return false;
 282                 }
 283             }
 284         }
 285 
 286         /**
 287          * Returns {@code true} if the given class loader type is
 288          * registered as parallel capable.
 289          */
 290         static boolean isRegistered(Class<? extends ClassLoader> c) {
 291             synchronized (loaderTypes) {
 292                 return loaderTypes.contains(c);
 293             }
 294         }
 295     }
 296 
 297     // Maps class name to the corresponding lock object when the current
 298     // class loader is parallel capable.
 299     // Note: VM also uses this field to decide if the current class loader
 300     // is parallel capable and the appropriate lock object for class loading.
 301     private final ConcurrentHashMap<String, Object> parallelLockMap;
 302 
 303     // Maps packages to certs
 304     private final ConcurrentHashMap<String, Certificate[]> package2certs;
 305 
 306     // Shared among all packages with unsigned classes
 307     private static final Certificate[] nocerts = new Certificate[0];
 308 
 309     // The classes loaded by this class loader. The only purpose of this table
 310     // is to keep the classes from being GC'ed until the loader is GC'ed.
 311     private final ArrayList<Class<?>> classes = new ArrayList<>();
 312 
 313     // The "default" domain. Set as the default ProtectionDomain on newly
 314     // created classes.
 315     private final ProtectionDomain defaultDomain =
 316         new ProtectionDomain(new CodeSource(null, (Certificate[]) null),
 317                              null, this, null);
 318 
 319     // Invoked by the VM to record every loaded class with this loader.
 320     void addClass(Class<?> c) {
 321         synchronized (classes) {
 322             classes.add(c);
 323         }
 324     }
 325 
 326     // The packages defined in this class loader.  Each package name is
 327     // mapped to its corresponding NamedPackage object.
 328     //
 329     // The value is a Package object if ClassLoader::definePackage,
 330     // Class::getPackage, ClassLoader::getDefinePackage(s) or
 331     // Package::getPackage(s) method is called to define it.
 332     // Otherwise, the value is a NamedPackage object.
 333     private final ConcurrentHashMap<String, NamedPackage> packages
 334             = new ConcurrentHashMap<>();
 335 
 336     /*
 337      * Returns a named package for the given module.
 338      */
 339     private NamedPackage getNamedPackage(String pn, Module m) {
 340         NamedPackage p = packages.get(pn);
 341         if (p == null) {
 342             p = new NamedPackage(pn, m);
 343 
 344             NamedPackage value = packages.putIfAbsent(pn, p);
 345             if (value != null) {
 346                 // Package object already be defined for the named package
 347                 p = value;
 348                 // if definePackage is called by this class loader to define
 349                 // a package in a named module, this will return Package
 350                 // object of the same name.  Package object may contain
 351                 // unexpected information but it does not impact the runtime.
 352                 // this assertion may be helpful for troubleshooting
 353                 assert value.module() == m;
 354             }
 355         }
 356         return p;
 357     }
 358 
 359     private static Void checkCreateClassLoader() {
 360         return checkCreateClassLoader(null);
 361     }
 362 
 363     private static Void checkCreateClassLoader(String name) {
 364         if (name != null && name.isEmpty()) {
 365             throw new IllegalArgumentException("name must be non-empty or null");
 366         }
 367 
 368         SecurityManager security = System.getSecurityManager();
 369         if (security != null) {
 370             security.checkCreateClassLoader();
 371         }
 372         return null;
 373     }
 374 
 375     private ClassLoader(Void unused, String name, ClassLoader parent) {
 376         this.name = name;
 377         this.parent = parent;
 378         this.unnamedModule = new Module(this);
 379         if (ParallelLoaders.isRegistered(this.getClass())) {
 380             parallelLockMap = new ConcurrentHashMap<>();
 381             assertionLock = new Object();
 382         } else {
 383             // no finer-grained lock; lock on the classloader instance
 384             parallelLockMap = null;
 385             assertionLock = this;
 386         }
 387         this.package2certs = new ConcurrentHashMap<>();
 388         this.nameAndId = nameAndId(this);
 389     }
 390 
 391     /**
 392      * If the defining loader has a name explicitly set then
 393      *       '<loader-name>' @<id>
 394      * If the defining loader has no name then
 395      *       <qualified-class-name> @<id>
 396      * If it's built-in loader then omit `@<id>` as there is only one instance.
 397      */
 398     private static String nameAndId(ClassLoader ld) {
 399         String nid = ld.getName() != null ? "\'" + ld.getName() + "\'"
 400                                           : ld.getClass().getName();
 401         if (!(ld instanceof BuiltinClassLoader)) {
 402             String id = Integer.toHexString(System.identityHashCode(ld));
 403             nid = nid + " @" + id;
 404         }
 405         return nid;
 406     }
 407 
 408     /**
 409      * Creates a new class loader of the specified name and using the
 410      * specified parent class loader for delegation.
 411      *
 412      * @apiNote If the parent is specified as {@code null} (for the
 413      * bootstrap class loader) then there is no guarantee that all platform
 414      * classes are visible.
 415      *
 416      * @param  name   class loader name; or {@code null} if not named
 417      * @param  parent the parent class loader
 418      *
 419      * @throws IllegalArgumentException if the given name is empty.
 420      *
 421      * @throws SecurityException
 422      *         If a security manager exists and its
 423      *         {@link SecurityManager#checkCreateClassLoader()}
 424      *         method doesn't allow creation of a new class loader.
 425      *
 426      * @since  9
 427      * @spec JPMS
 428      */
 429     protected ClassLoader(String name, ClassLoader parent) {
 430         this(checkCreateClassLoader(name), name, parent);
 431     }
 432 
 433     /**
 434      * Creates a new class loader using the specified parent class loader for
 435      * delegation.
 436      *
 437      * <p> If there is a security manager, its {@link
 438      * SecurityManager#checkCreateClassLoader() checkCreateClassLoader} method
 439      * is invoked.  This may result in a security exception.  </p>
 440      *
 441      * @apiNote If the parent is specified as {@code null} (for the
 442      * bootstrap class loader) then there is no guarantee that all platform
 443      * classes are visible.
 444      *
 445      * @param  parent
 446      *         The parent class loader
 447      *
 448      * @throws SecurityException
 449      *         If a security manager exists and its
 450      *         {@code checkCreateClassLoader} method doesn't allow creation
 451      *         of a new class loader.
 452      *
 453      * @since  1.2
 454      */
 455     protected ClassLoader(ClassLoader parent) {
 456         this(checkCreateClassLoader(), null, parent);
 457     }
 458 
 459     /**
 460      * Creates a new class loader using the {@code ClassLoader} returned by
 461      * the method {@link #getSystemClassLoader()
 462      * getSystemClassLoader()} as the parent class loader.
 463      *
 464      * <p> If there is a security manager, its {@link
 465      * SecurityManager#checkCreateClassLoader()
 466      * checkCreateClassLoader} method is invoked.  This may result in
 467      * a security exception.  </p>
 468      *
 469      * @throws  SecurityException
 470      *          If a security manager exists and its
 471      *          {@code checkCreateClassLoader} method doesn't allow creation
 472      *          of a new class loader.
 473      */
 474     protected ClassLoader() {
 475         this(checkCreateClassLoader(), null, getSystemClassLoader());
 476     }
 477 
 478     /**
 479      * Returns the name of this class loader or {@code null} if
 480      * this class loader is not named.
 481      *
 482      * @apiNote This method is non-final for compatibility.  If this
 483      * method is overridden, this method must return the same name
 484      * as specified when this class loader was instantiated.
 485      *
 486      * @return name of this class loader; or {@code null} if
 487      * this class loader is not named.
 488      *
 489      * @since 9
 490      * @spec JPMS
 491      */
 492     public String getName() {
 493         return name;
 494     }
 495 
 496     // package-private used by StackTraceElement to avoid
 497     // calling the overrideable getName method
 498     final String name() {
 499         return name;
 500     }
 501 
 502     // -- Class --
 503 
 504     /**
 505      * Loads the class with the specified <a href="#binary-name">binary name</a>.
 506      * This method searches for classes in the same manner as the {@link
 507      * #loadClass(String, boolean)} method.  It is invoked by the Java virtual
 508      * machine to resolve class references.  Invoking this method is equivalent
 509      * to invoking {@link #loadClass(String, boolean) loadClass(name,
 510      * false)}.
 511      *
 512      * @param   name
 513      *          The <a href="#binary-name">binary name</a> of the class
 514      *
 515      * @return  The resulting {@code Class} object
 516      *
 517      * @throws  ClassNotFoundException
 518      *          If the class was not found
 519      */
 520     public Class<?> loadClass(String name) throws ClassNotFoundException {
 521         return loadClass(name, false);
 522     }
 523 
 524     /**
 525      * Loads the class with the specified <a href="#binary-name">binary name</a>.  The
 526      * default implementation of this method searches for classes in the
 527      * following order:
 528      *
 529      * <ol>
 530      *
 531      *   <li><p> Invoke {@link #findLoadedClass(String)} to check if the class
 532      *   has already been loaded.  </p></li>
 533      *
 534      *   <li><p> Invoke the {@link #loadClass(String) loadClass} method
 535      *   on the parent class loader.  If the parent is {@code null} the class
 536      *   loader built into the virtual machine is used, instead.  </p></li>
 537      *
 538      *   <li><p> Invoke the {@link #findClass(String)} method to find the
 539      *   class.  </p></li>
 540      *
 541      * </ol>
 542      *
 543      * <p> If the class was found using the above steps, and the
 544      * {@code resolve} flag is true, this method will then invoke the {@link
 545      * #resolveClass(Class)} method on the resulting {@code Class} object.
 546      *
 547      * <p> Subclasses of {@code ClassLoader} are encouraged to override {@link
 548      * #findClass(String)}, rather than this method.  </p>
 549      *
 550      * <p> Unless overridden, this method synchronizes on the result of
 551      * {@link #getClassLoadingLock getClassLoadingLock} method
 552      * during the entire class loading process.
 553      *
 554      * @param   name
 555      *          The <a href="#binary-name">binary name</a> of the class
 556      *
 557      * @param   resolve
 558      *          If {@code true} then resolve the class
 559      *
 560      * @return  The resulting {@code Class} object
 561      *
 562      * @throws  ClassNotFoundException
 563      *          If the class could not be found
 564      */
 565     protected Class<?> loadClass(String name, boolean resolve)
 566         throws ClassNotFoundException
 567     {
 568         synchronized (getClassLoadingLock(name)) {
 569             // First, check if the class has already been loaded
 570             Class<?> c = findLoadedClass(name);
 571             if (c == null) {
 572                 long t0 = System.nanoTime();
 573                 try {
 574                     if (parent != null) {
 575                         c = parent.loadClass(name, false);
 576                     } else {
 577                         c = findBootstrapClassOrNull(name);
 578                     }
 579                 } catch (ClassNotFoundException e) {
 580                     // ClassNotFoundException thrown if class not found
 581                     // from the non-null parent class loader
 582                 }
 583 
 584                 if (c == null) {
 585                     // If still not found, then invoke findClass in order
 586                     // to find the class.
 587                     long t1 = System.nanoTime();
 588                     c = findClass(name);
 589 
 590                     // this is the defining class loader; record the stats
 591                     PerfCounter.getParentDelegationTime().addTime(t1 - t0);
 592                     PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
 593                     PerfCounter.getFindClasses().increment();
 594                 }
 595             }
 596             if (resolve) {
 597                 resolveClass(c);
 598             }
 599             return c;
 600         }
 601     }
 602 
 603     /**
 604      * Loads the class with the specified <a href="#binary-name">binary name</a>
 605      * in a module defined to this class loader.  This method returns {@code null}
 606      * if the class could not be found.
 607      *
 608      * @apiNote This method does not delegate to the parent class loader.
 609      *
 610      * @implSpec The default implementation of this method searches for classes
 611      * in the following order:
 612      *
 613      * <ol>
 614      *   <li>Invoke {@link #findLoadedClass(String)} to check if the class
 615      *   has already been loaded.</li>
 616      *   <li>Invoke the {@link #findClass(String, String)} method to find the
 617      *   class in the given module.</li>
 618      * </ol>
 619      *
 620      * @param  module
 621      *         The module
 622      * @param  name
 623      *         The <a href="#binary-name">binary name</a> of the class
 624      *
 625      * @return The resulting {@code Class} object in a module defined by
 626      *         this class loader, or {@code null} if the class could not be found.
 627      */
 628     final Class<?> loadClass(Module module, String name) {
 629         synchronized (getClassLoadingLock(name)) {
 630             // First, check if the class has already been loaded
 631             Class<?> c = findLoadedClass(name);
 632             if (c == null) {
 633                 c = findClass(module.getName(), name);
 634             }
 635             if (c != null && c.getModule() == module) {
 636                 return c;
 637             } else {
 638                 return null;
 639             }
 640         }
 641     }
 642 
 643     /**
 644      * Returns the lock object for class loading operations.
 645      * For backward compatibility, the default implementation of this method
 646      * behaves as follows. If this ClassLoader object is registered as
 647      * parallel capable, the method returns a dedicated object associated
 648      * with the specified class name. Otherwise, the method returns this
 649      * ClassLoader object.
 650      *
 651      * @param  className
 652      *         The name of the to-be-loaded class
 653      *
 654      * @return the lock for class loading operations
 655      *
 656      * @throws NullPointerException
 657      *         If registered as parallel capable and {@code className} is null
 658      *
 659      * @see #loadClass(String, boolean)
 660      *
 661      * @since  1.7
 662      */
 663     protected Object getClassLoadingLock(String className) {
 664         Object lock = this;
 665         if (parallelLockMap != null) {
 666             Object newLock = new Object();
 667             lock = parallelLockMap.putIfAbsent(className, newLock);
 668             if (lock == null) {
 669                 lock = newLock;
 670             }
 671         }
 672         return lock;
 673     }
 674 
 675     // Invoked by the VM after loading class with this loader.
 676     private void checkPackageAccess(Class<?> cls, ProtectionDomain pd) {
 677         final SecurityManager sm = System.getSecurityManager();
 678         if (sm != null) {
 679             if (ReflectUtil.isNonPublicProxyClass(cls)) {
 680                 for (Class<?> intf: cls.getInterfaces()) {
 681                     checkPackageAccess(intf, pd);
 682                 }
 683                 return;
 684             }
 685 
 686             final String packageName = cls.getPackageName();
 687             if (!packageName.isEmpty()) {
 688                 AccessController.doPrivileged(new PrivilegedAction<>() {
 689                     public Void run() {
 690                         sm.checkPackageAccess(packageName);
 691                         return null;
 692                     }
 693                 }, new AccessControlContext(new ProtectionDomain[] {pd}));
 694             }
 695         }
 696     }
 697 
 698     /**
 699      * Finds the class with the specified <a href="#binary-name">binary name</a>.
 700      * This method should be overridden by class loader implementations that
 701      * follow the delegation model for loading classes, and will be invoked by
 702      * the {@link #loadClass loadClass} method after checking the
 703      * parent class loader for the requested class.
 704      *
 705      * @implSpec The default implementation throws {@code ClassNotFoundException}.
 706      *
 707      * @param   name
 708      *          The <a href="#binary-name">binary name</a> of the class
 709      *
 710      * @return  The resulting {@code Class} object
 711      *
 712      * @throws  ClassNotFoundException
 713      *          If the class could not be found
 714      *
 715      * @since  1.2
 716      */
 717     protected Class<?> findClass(String name) throws ClassNotFoundException {
 718         throw new ClassNotFoundException(name);
 719     }
 720 
 721     /**
 722      * Finds the class with the given <a href="#binary-name">binary name</a>
 723      * in a module defined to this class loader.
 724      * Class loader implementations that support loading from modules
 725      * should override this method.
 726      *
 727      * @apiNote This method returns {@code null} rather than throwing
 728      *          {@code ClassNotFoundException} if the class could not be found.
 729      *
 730      * @implSpec The default implementation attempts to find the class by
 731      * invoking {@link #findClass(String)} when the {@code moduleName} is
 732      * {@code null}. It otherwise returns {@code null}.
 733      *
 734      * @param  moduleName
 735      *         The module name; or {@code null} to find the class in the
 736      *         {@linkplain #getUnnamedModule() unnamed module} for this
 737      *         class loader
 738 
 739      * @param  name
 740      *         The <a href="#binary-name">binary name</a> of the class
 741      *
 742      * @return The resulting {@code Class} object, or {@code null}
 743      *         if the class could not be found.
 744      *
 745      * @since 9
 746      * @spec JPMS
 747      */
 748     protected Class<?> findClass(String moduleName, String name) {
 749         if (moduleName == null) {
 750             try {
 751                 return findClass(name);
 752             } catch (ClassNotFoundException ignore) { }
 753         }
 754         return null;
 755     }
 756 
 757 
 758     /**
 759      * Converts an array of bytes into an instance of class {@code Class}.
 760      * Before the {@code Class} can be used it must be resolved.  This method
 761      * is deprecated in favor of the version that takes a <a
 762      * href="#binary-name">binary name</a> as its first argument, and is more secure.
 763      *
 764      * @param  b
 765      *         The bytes that make up the class data.  The bytes in positions
 766      *         {@code off} through {@code off+len-1} should have the format
 767      *         of a valid class file as defined by
 768      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 769      *
 770      * @param  off
 771      *         The start offset in {@code b} of the class data
 772      *
 773      * @param  len
 774      *         The length of the class data
 775      *
 776      * @return  The {@code Class} object that was created from the specified
 777      *          class data
 778      *
 779      * @throws  ClassFormatError
 780      *          If the data did not contain a valid class
 781      *
 782      * @throws  IndexOutOfBoundsException
 783      *          If either {@code off} or {@code len} is negative, or if
 784      *          {@code off+len} is greater than {@code b.length}.
 785      *
 786      * @throws  SecurityException
 787      *          If an attempt is made to add this class to a package that
 788      *          contains classes that were signed by a different set of
 789      *          certificates than this class, or if an attempt is made
 790      *          to define a class in a package with a fully-qualified name
 791      *          that starts with "{@code java.}".
 792      *
 793      * @see  #loadClass(String, boolean)
 794      * @see  #resolveClass(Class)
 795      *
 796      * @deprecated  Replaced by {@link #defineClass(String, byte[], int, int)
 797      * defineClass(String, byte[], int, int)}
 798      */
 799     @Deprecated(since="1.1")
 800     protected final Class<?> defineClass(byte[] b, int off, int len)
 801         throws ClassFormatError
 802     {
 803         return defineClass(null, b, off, len, null);
 804     }
 805 
 806     /**
 807      * Converts an array of bytes into an instance of class {@code Class}.
 808      * Before the {@code Class} can be used it must be resolved.
 809      *
 810      * <p> This method assigns a default {@link java.security.ProtectionDomain
 811      * ProtectionDomain} to the newly defined class.  The
 812      * {@code ProtectionDomain} is effectively granted the same set of
 813      * permissions returned when {@link
 814      * java.security.Policy#getPermissions(java.security.CodeSource)
 815      * Policy.getPolicy().getPermissions(new CodeSource(null, null))}
 816      * is invoked.  The default protection domain is created on the first invocation
 817      * of {@link #defineClass(String, byte[], int, int) defineClass},
 818      * and re-used on subsequent invocations.
 819      *
 820      * <p> To assign a specific {@code ProtectionDomain} to the class, use
 821      * the {@link #defineClass(String, byte[], int, int,
 822      * java.security.ProtectionDomain) defineClass} method that takes a
 823      * {@code ProtectionDomain} as one of its arguments.  </p>
 824      *
 825      * <p>
 826      * This method defines a package in this class loader corresponding to the
 827      * package of the {@code Class} (if such a package has not already been defined
 828      * in this class loader). The name of the defined package is derived from
 829      * the <a href="#binary-name">binary name</a> of the class specified by
 830      * the byte array {@code b}.
 831      * Other properties of the defined package are as specified by {@link Package}.
 832      *
 833      * @param  name
 834      *         The expected <a href="#binary-name">binary name</a> of the class, or
 835      *         {@code null} if not known
 836      *
 837      * @param  b
 838      *         The bytes that make up the class data.  The bytes in positions
 839      *         {@code off} through {@code off+len-1} should have the format
 840      *         of a valid class file as defined by
 841      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 842      *
 843      * @param  off
 844      *         The start offset in {@code b} of the class data
 845      *
 846      * @param  len
 847      *         The length of the class data
 848      *
 849      * @return  The {@code Class} object that was created from the specified
 850      *          class data.
 851      *
 852      * @throws  ClassFormatError
 853      *          If the data did not contain a valid class
 854      *
 855      * @throws  IndexOutOfBoundsException
 856      *          If either {@code off} or {@code len} is negative, or if
 857      *          {@code off+len} is greater than {@code b.length}.
 858      *
 859      * @throws  SecurityException
 860      *          If an attempt is made to add this class to a package that
 861      *          contains classes that were signed by a different set of
 862      *          certificates than this class (which is unsigned), or if
 863      *          {@code name} begins with "{@code java.}".
 864      *
 865      * @see  #loadClass(String, boolean)
 866      * @see  #resolveClass(Class)
 867      * @see  java.security.CodeSource
 868      * @see  java.security.SecureClassLoader
 869      *
 870      * @since  1.1
 871      * @revised 9
 872      * @spec JPMS
 873      */
 874     protected final Class<?> defineClass(String name, byte[] b, int off, int len)
 875         throws ClassFormatError
 876     {
 877         return defineClass(name, b, off, len, null);
 878     }
 879 
 880     /* Determine protection domain, and check that:
 881         - not define java.* class,
 882         - signer of this class matches signers for the rest of the classes in
 883           package.
 884     */
 885     private ProtectionDomain preDefineClass(String name,
 886                                             ProtectionDomain pd)
 887     {
 888         if (!checkName(name))
 889             throw new NoClassDefFoundError("IllegalName: " + name);
 890 
 891         // Note:  Checking logic in java.lang.invoke.MemberName.checkForTypeAlias
 892         // relies on the fact that spoofing is impossible if a class has a name
 893         // of the form "java.*"
 894         if ((name != null) && name.startsWith("java.")
 895                 && this != getBuiltinPlatformClassLoader()) {
 896             throw new SecurityException
 897                 ("Prohibited package name: " +
 898                  name.substring(0, name.lastIndexOf('.')));
 899         }
 900         if (pd == null) {
 901             pd = defaultDomain;
 902         }
 903 
 904         if (name != null) {
 905             checkCerts(name, pd.getCodeSource());
 906         }
 907 
 908         return pd;
 909     }
 910 
 911     private String defineClassSourceLocation(ProtectionDomain pd) {
 912         CodeSource cs = pd.getCodeSource();
 913         String source = null;
 914         if (cs != null && cs.getLocation() != null) {
 915             source = cs.getLocation().toString();
 916         }
 917         return source;
 918     }
 919 
 920     private void postDefineClass(Class<?> c, ProtectionDomain pd) {
 921         // define a named package, if not present
 922         getNamedPackage(c.getPackageName(), c.getModule());
 923 
 924         if (pd.getCodeSource() != null) {
 925             Certificate certs[] = pd.getCodeSource().getCertificates();
 926             if (certs != null)
 927                 setSigners(c, certs);
 928         }
 929     }
 930 
 931     /**
 932      * Converts an array of bytes into an instance of class {@code Class},
 933      * with a given {@code ProtectionDomain}.
 934      *
 935      * <p> If the given {@code ProtectionDomain} is {@code null},
 936      * then a default protection domain will be assigned to the class as specified
 937      * in the documentation for {@link #defineClass(String, byte[], int, int)}.
 938      * Before the class can be used it must be resolved.
 939      *
 940      * <p> The first class defined in a package determines the exact set of
 941      * certificates that all subsequent classes defined in that package must
 942      * contain.  The set of certificates for a class is obtained from the
 943      * {@link java.security.CodeSource CodeSource} within the
 944      * {@code ProtectionDomain} of the class.  Any classes added to that
 945      * package must contain the same set of certificates or a
 946      * {@code SecurityException} will be thrown.  Note that if
 947      * {@code name} is {@code null}, this check is not performed.
 948      * You should always pass in the <a href="#binary-name">binary name</a> of the
 949      * class you are defining as well as the bytes.  This ensures that the
 950      * class you are defining is indeed the class you think it is.
 951      *
 952      * <p> If the specified {@code name} begins with "{@code java.}", it can
 953      * only be defined by the {@linkplain #getPlatformClassLoader()
 954      * platform class loader} or its ancestors; otherwise {@code SecurityException}
 955      * will be thrown.  If {@code name} is not {@code null}, it must be equal to
 956      * the <a href="#binary-name">binary name</a> of the class
 957      * specified by the byte array {@code b}, otherwise a {@link
 958      * NoClassDefFoundError NoClassDefFoundError} will be thrown.
 959      *
 960      * <p> This method defines a package in this class loader corresponding to the
 961      * package of the {@code Class} (if such a package has not already been defined
 962      * in this class loader). The name of the defined package is derived from
 963      * the <a href="#binary-name">binary name</a> of the class specified by
 964      * the byte array {@code b}.
 965      * Other properties of the defined package are as specified by {@link Package}.
 966      *
 967      * @param  name
 968      *         The expected <a href="#binary-name">binary name</a> of the class, or
 969      *         {@code null} if not known
 970      *
 971      * @param  b
 972      *         The bytes that make up the class data. The bytes in positions
 973      *         {@code off} through {@code off+len-1} should have the format
 974      *         of a valid class file as defined by
 975      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
 976      *
 977      * @param  off
 978      *         The start offset in {@code b} of the class data
 979      *
 980      * @param  len
 981      *         The length of the class data
 982      *
 983      * @param  protectionDomain
 984      *         The {@code ProtectionDomain} of the class
 985      *
 986      * @return  The {@code Class} object created from the data,
 987      *          and {@code ProtectionDomain}.
 988      *
 989      * @throws  ClassFormatError
 990      *          If the data did not contain a valid class
 991      *
 992      * @throws  NoClassDefFoundError
 993      *          If {@code name} is not {@code null} and not equal to the
 994      *          <a href="#binary-name">binary name</a> of the class specified by {@code b}
 995      *
 996      * @throws  IndexOutOfBoundsException
 997      *          If either {@code off} or {@code len} is negative, or if
 998      *          {@code off+len} is greater than {@code b.length}.
 999      *
1000      * @throws  SecurityException
1001      *          If an attempt is made to add this class to a package that
1002      *          contains classes that were signed by a different set of
1003      *          certificates than this class, or if {@code name} begins with
1004      *          "{@code java.}" and this class loader is not the platform
1005      *          class loader or its ancestor.
1006      *
1007      * @revised 9
1008      * @spec JPMS
1009      */
1010     protected final Class<?> defineClass(String name, byte[] b, int off, int len,
1011                                          ProtectionDomain protectionDomain)
1012         throws ClassFormatError
1013     {
1014         protectionDomain = preDefineClass(name, protectionDomain);
1015         String source = defineClassSourceLocation(protectionDomain);
1016         Class<?> c = defineClass1(this, name, b, off, len, protectionDomain, source);
1017         postDefineClass(c, protectionDomain);
1018         return c;
1019     }
1020 
1021     /**
1022      * Converts a {@link java.nio.ByteBuffer ByteBuffer} into an instance
1023      * of class {@code Class}, with the given {@code ProtectionDomain}.
1024      * If the given {@code ProtectionDomain} is {@code null}, then a default
1025      * protection domain will be assigned to the class as
1026      * specified in the documentation for {@link #defineClass(String, byte[],
1027      * int, int)}.  Before the class can be used it must be resolved.
1028      *
1029      * <p>The rules about the first class defined in a package determining the
1030      * set of certificates for the package, the restrictions on class names,
1031      * and the defined package of the class
1032      * are identical to those specified in the documentation for {@link
1033      * #defineClass(String, byte[], int, int, ProtectionDomain)}.
1034      *
1035      * <p> An invocation of this method of the form
1036      * <i>cl</i>{@code .defineClass(}<i>name</i>{@code ,}
1037      * <i>bBuffer</i>{@code ,} <i>pd</i>{@code )} yields exactly the same
1038      * result as the statements
1039      *
1040      *<p> <code>
1041      * ...<br>
1042      * byte[] temp = new byte[bBuffer.{@link
1043      * java.nio.ByteBuffer#remaining remaining}()];<br>
1044      *     bBuffer.{@link java.nio.ByteBuffer#get(byte[])
1045      * get}(temp);<br>
1046      *     return {@link #defineClass(String, byte[], int, int, ProtectionDomain)
1047      * cl.defineClass}(name, temp, 0,
1048      * temp.length, pd);<br>
1049      * </code></p>
1050      *
1051      * @param  name
1052      *         The expected <a href="#binary-name">binary name</a>. of the class, or
1053      *         {@code null} if not known
1054      *
1055      * @param  b
1056      *         The bytes that make up the class data. The bytes from positions
1057      *         {@code b.position()} through {@code b.position() + b.limit() -1
1058      *         } should have the format of a valid class file as defined by
1059      *         <cite>The Java&trade; Virtual Machine Specification</cite>.
1060      *
1061      * @param  protectionDomain
1062      *         The {@code ProtectionDomain} of the class, or {@code null}.
1063      *
1064      * @return  The {@code Class} object created from the data,
1065      *          and {@code ProtectionDomain}.
1066      *
1067      * @throws  ClassFormatError
1068      *          If the data did not contain a valid class.
1069      *
1070      * @throws  NoClassDefFoundError
1071      *          If {@code name} is not {@code null} and not equal to the
1072      *          <a href="#binary-name">binary name</a> of the class specified by {@code b}
1073      *
1074      * @throws  SecurityException
1075      *          If an attempt is made to add this class to a package that
1076      *          contains classes that were signed by a different set of
1077      *          certificates than this class, or if {@code name} begins with
1078      *          "{@code java.}".
1079      *
1080      * @see      #defineClass(String, byte[], int, int, ProtectionDomain)
1081      *
1082      * @since  1.5
1083      * @revised 9
1084      * @spec JPMS
1085      */
1086     protected final Class<?> defineClass(String name, java.nio.ByteBuffer b,
1087                                          ProtectionDomain protectionDomain)
1088         throws ClassFormatError
1089     {
1090         int len = b.remaining();
1091 
1092         // Use byte[] if not a direct ByteBuffer:
1093         if (!b.isDirect()) {
1094             if (b.hasArray()) {
1095                 return defineClass(name, b.array(),
1096                                    b.position() + b.arrayOffset(), len,
1097                                    protectionDomain);
1098             } else {
1099                 // no array, or read-only array
1100                 byte[] tb = new byte[len];
1101                 b.get(tb);  // get bytes out of byte buffer.
1102                 return defineClass(name, tb, 0, len, protectionDomain);
1103             }
1104         }
1105 
1106         protectionDomain = preDefineClass(name, protectionDomain);
1107         String source = defineClassSourceLocation(protectionDomain);
1108         Class<?> c = defineClass2(this, name, b, b.position(), len, protectionDomain, source);
1109         postDefineClass(c, protectionDomain);
1110         return c;
1111     }
1112 
1113     static native Class<?> defineClass1(ClassLoader loader, String name, byte[] b, int off, int len,
1114                                         ProtectionDomain pd, String source);
1115 
1116     static native Class<?> defineClass2(ClassLoader loader, String name, java.nio.ByteBuffer b,
1117                                         int off, int len, ProtectionDomain pd,
1118                                         String source);
1119 
1120     // true if the name is null or has the potential to be a valid binary name
1121     private boolean checkName(String name) {
1122         if ((name == null) || (name.isEmpty()))
1123             return true;
1124         if ((name.indexOf('/') != -1) || (name.charAt(0) == '['))
1125             return false;
1126         return true;
1127     }
1128 
1129     private void checkCerts(String name, CodeSource cs) {
1130         int i = name.lastIndexOf('.');
1131         String pname = (i == -1) ? "" : name.substring(0, i);
1132 
1133         Certificate[] certs = null;
1134         if (cs != null) {
1135             certs = cs.getCertificates();
1136         }
1137         certs = certs == null ? nocerts : certs;
1138         Certificate[] pcerts = package2certs.putIfAbsent(pname, certs);
1139         if (pcerts != null && !compareCerts(pcerts, certs)) {
1140             throw new SecurityException("class \"" + name
1141                 + "\"'s signer information does not match signer information"
1142                 + " of other classes in the same package");
1143         }
1144     }
1145 
1146     /**
1147      * check to make sure the certs for the new class (certs) are the same as
1148      * the certs for the first class inserted in the package (pcerts)
1149      */
1150     private boolean compareCerts(Certificate[] pcerts, Certificate[] certs) {
1151         // empty array fast-path
1152         if (certs.length == 0)
1153             return pcerts.length == 0;
1154 
1155         // the length must be the same at this point
1156         if (certs.length != pcerts.length)
1157             return false;
1158 
1159         // go through and make sure all the certs in one array
1160         // are in the other and vice-versa.
1161         boolean match;
1162         for (Certificate cert : certs) {
1163             match = false;
1164             for (Certificate pcert : pcerts) {
1165                 if (cert.equals(pcert)) {
1166                     match = true;
1167                     break;
1168                 }
1169             }
1170             if (!match) return false;
1171         }
1172 
1173         // now do the same for pcerts
1174         for (Certificate pcert : pcerts) {
1175             match = false;
1176             for (Certificate cert : certs) {
1177                 if (pcert.equals(cert)) {
1178                     match = true;
1179                     break;
1180                 }
1181             }
1182             if (!match) return false;
1183         }
1184 
1185         return true;
1186     }
1187 
1188     /**
1189      * Links the specified class.  This (misleadingly named) method may be
1190      * used by a class loader to link a class.  If the class {@code c} has
1191      * already been linked, then this method simply returns. Otherwise, the
1192      * class is linked as described in the "Execution" chapter of
1193      * <cite>The Java&trade; Language Specification</cite>.
1194      *
1195      * @param  c
1196      *         The class to link
1197      *
1198      * @throws  NullPointerException
1199      *          If {@code c} is {@code null}.
1200      *
1201      * @see  #defineClass(String, byte[], int, int)
1202      */
1203     protected final void resolveClass(Class<?> c) {
1204         if (c == null) {
1205             throw new NullPointerException();
1206         }
1207     }
1208 
1209     /**
1210      * Finds a class with the specified <a href="#binary-name">binary name</a>,
1211      * loading it if necessary.
1212      *
1213      * <p> This method loads the class through the system class loader (see
1214      * {@link #getSystemClassLoader()}).  The {@code Class} object returned
1215      * might have more than one {@code ClassLoader} associated with it.
1216      * Subclasses of {@code ClassLoader} need not usually invoke this method,
1217      * because most class loaders need to override just {@link
1218      * #findClass(String)}.  </p>
1219      *
1220      * @param  name
1221      *         The <a href="#binary-name">binary name</a> of the class
1222      *
1223      * @return  The {@code Class} object for the specified {@code name}
1224      *
1225      * @throws  ClassNotFoundException
1226      *          If the class could not be found
1227      *
1228      * @see  #ClassLoader(ClassLoader)
1229      * @see  #getParent()
1230      */
1231     protected final Class<?> findSystemClass(String name)
1232         throws ClassNotFoundException
1233     {
1234         return getSystemClassLoader().loadClass(name);
1235     }
1236 
1237     /**
1238      * Returns a class loaded by the bootstrap class loader;
1239      * or return null if not found.
1240      */
1241     Class<?> findBootstrapClassOrNull(String name) {
1242         if (!checkName(name)) return null;
1243 
1244         return findBootstrapClass(name);
1245     }
1246 
1247     // return null if not found
1248     private native Class<?> findBootstrapClass(String name);
1249 
1250     /**
1251      * Returns the class with the given <a href="#binary-name">binary name</a> if this
1252      * loader has been recorded by the Java virtual machine as an initiating
1253      * loader of a class with that <a href="#binary-name">binary name</a>.  Otherwise
1254      * {@code null} is returned.
1255      *
1256      * @param  name
1257      *         The <a href="#binary-name">binary name</a> of the class
1258      *
1259      * @return  The {@code Class} object, or {@code null} if the class has
1260      *          not been loaded
1261      *
1262      * @since  1.1
1263      */
1264     protected final Class<?> findLoadedClass(String name) {
1265         if (!checkName(name))
1266             return null;
1267         return findLoadedClass0(name);
1268     }
1269 
1270     private final native Class<?> findLoadedClass0(String name);
1271 
1272     /**
1273      * Sets the signers of a class.  This should be invoked after defining a
1274      * class.
1275      *
1276      * @param  c
1277      *         The {@code Class} object
1278      *
1279      * @param  signers
1280      *         The signers for the class
1281      *
1282      * @since  1.1
1283      */
1284     protected final void setSigners(Class<?> c, Object[] signers) {
1285         c.setSigners(signers);
1286     }
1287 
1288 
1289     // -- Resources --
1290 
1291     /**
1292      * Returns a URL to a resource in a module defined to this class loader.
1293      * Class loader implementations that support loading from modules
1294      * should override this method.
1295      *
1296      * @apiNote This method is the basis for the {@link
1297      * Class#getResource Class.getResource}, {@link Class#getResourceAsStream
1298      * Class.getResourceAsStream}, and {@link Module#getResourceAsStream
1299      * Module.getResourceAsStream} methods. It is not subject to the rules for
1300      * encapsulation specified by {@code Module.getResourceAsStream}.
1301      *
1302      * @implSpec The default implementation attempts to find the resource by
1303      * invoking {@link #findResource(String)} when the {@code moduleName} is
1304      * {@code null}. It otherwise returns {@code null}.
1305      *
1306      * @param  moduleName
1307      *         The module name; or {@code null} to find a resource in the
1308      *         {@linkplain #getUnnamedModule() unnamed module} for this
1309      *         class loader
1310      * @param  name
1311      *         The resource name
1312      *
1313      * @return A URL to the resource; {@code null} if the resource could not be
1314      *         found, a URL could not be constructed to locate the resource,
1315      *         access to the resource is denied by the security manager, or
1316      *         there isn't a module of the given name defined to the class
1317      *         loader.
1318      *
1319      * @throws IOException
1320      *         If I/O errors occur
1321      *
1322      * @see java.lang.module.ModuleReader#find(String)
1323      * @since 9
1324      * @spec JPMS
1325      */
1326     protected URL findResource(String moduleName, String name) throws IOException {
1327         if (moduleName == null) {
1328             return findResource(name);
1329         } else {
1330             return null;
1331         }
1332     }
1333 
1334     /**
1335      * Finds the resource with the given name.  A resource is some data
1336      * (images, audio, text, etc) that can be accessed by class code in a way
1337      * that is independent of the location of the code.
1338      *
1339      * <p> The name of a resource is a '{@code /}'-separated path name that
1340      * identifies the resource. </p>
1341      *
1342      * <p> Resources in named modules are subject to the encapsulation rules
1343      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1344      * Additionally, and except for the special case where the resource has a
1345      * name ending with "{@code .class}", this method will only find resources in
1346      * packages of named modules when the package is {@link Module#isOpen(String)
1347      * opened} unconditionally (even if the caller of this method is in the
1348      * same module as the resource). </p>
1349      *
1350      * @implSpec The default implementation will first search the parent class
1351      * loader for the resource; if the parent is {@code null} the path of the
1352      * class loader built into the virtual machine is searched. If not found,
1353      * this method will invoke {@link #findResource(String)} to find the resource.
1354      *
1355      * @apiNote Where several modules are defined to the same class loader,
1356      * and where more than one module contains a resource with the given name,
1357      * then the ordering that modules are searched is not specified and may be
1358      * very unpredictable.
1359      * When overriding this method it is recommended that an implementation
1360      * ensures that any delegation is consistent with the {@link
1361      * #getResources(java.lang.String) getResources(String)} method.
1362      *
1363      * @param  name
1364      *         The resource name
1365      *
1366      * @return  {@code URL} object for reading the resource; {@code null} if
1367      *          the resource could not be found, a {@code URL} could not be
1368      *          constructed to locate the resource, the resource is in a package
1369      *          that is not opened unconditionally, or access to the resource is
1370      *          denied by the security manager.
1371      *
1372      * @throws  NullPointerException If {@code name} is {@code null}
1373      *
1374      * @since  1.1
1375      * @revised 9
1376      * @spec JPMS
1377      */
1378     public URL getResource(String name) {
1379         Objects.requireNonNull(name);
1380         URL url;
1381         if (parent != null) {
1382             url = parent.getResource(name);
1383         } else {
1384             url = BootLoader.findResource(name);
1385         }
1386         if (url == null) {
1387             url = findResource(name);
1388         }
1389         return url;
1390     }
1391 
1392     /**
1393      * Finds all the resources with the given name. A resource is some data
1394      * (images, audio, text, etc) that can be accessed by class code in a way
1395      * that is independent of the location of the code.
1396      *
1397      * <p> The name of a resource is a {@code /}-separated path name that
1398      * identifies the resource. </p>
1399      *
1400      * <p> Resources in named modules are subject to the encapsulation rules
1401      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1402      * Additionally, and except for the special case where the resource has a
1403      * name ending with "{@code .class}", this method will only find resources in
1404      * packages of named modules when the package is {@link Module#isOpen(String)
1405      * opened} unconditionally (even if the caller of this method is in the
1406      * same module as the resource). </p>
1407      *
1408      * @implSpec The default implementation will first search the parent class
1409      * loader for the resource; if the parent is {@code null} the path of the
1410      * class loader built into the virtual machine is searched. It then
1411      * invokes {@link #findResources(String)} to find the resources with the
1412      * name in this class loader. It returns an enumeration whose elements
1413      * are the URLs found by searching the parent class loader followed by
1414      * the elements found with {@code findResources}.
1415      *
1416      * @apiNote Where several modules are defined to the same class loader,
1417      * and where more than one module contains a resource with the given name,
1418      * then the ordering is not specified and may be very unpredictable.
1419      * When overriding this method it is recommended that an
1420      * implementation ensures that any delegation is consistent with the {@link
1421      * #getResource(java.lang.String) getResource(String)} method. This should
1422      * ensure that the first element returned by the Enumeration's
1423      * {@code nextElement} method is the same resource that the
1424      * {@code getResource(String)} method would return.
1425      *
1426      * @param  name
1427      *         The resource name
1428      *
1429      * @return  An enumeration of {@link java.net.URL URL} objects for the
1430      *          resource. If no resources could be found, the enumeration will
1431      *          be empty. Resources for which a {@code URL} cannot be
1432      *          constructed, are in a package that is not opened
1433      *          unconditionally, or access to the resource is denied by the
1434      *          security manager, are not returned in the enumeration.
1435      *
1436      * @throws  IOException
1437      *          If I/O errors occur
1438      * @throws  NullPointerException If {@code name} is {@code null}
1439      *
1440      * @since  1.2
1441      * @revised 9
1442      * @spec JPMS
1443      */
1444     public Enumeration<URL> getResources(String name) throws IOException {
1445         Objects.requireNonNull(name);
1446         @SuppressWarnings("unchecked")
1447         Enumeration<URL>[] tmp = (Enumeration<URL>[]) new Enumeration<?>[2];
1448         if (parent != null) {
1449             tmp[0] = parent.getResources(name);
1450         } else {
1451             tmp[0] = BootLoader.findResources(name);
1452         }
1453         tmp[1] = findResources(name);
1454 
1455         return new CompoundEnumeration<>(tmp);
1456     }
1457 
1458     /**
1459      * Returns a stream whose elements are the URLs of all the resources with
1460      * the given name. A resource is some data (images, audio, text, etc) that
1461      * can be accessed by class code in a way that is independent of the
1462      * location of the code.
1463      *
1464      * <p> The name of a resource is a {@code /}-separated path name that
1465      * identifies the resource.
1466      *
1467      * <p> The resources will be located when the returned stream is evaluated.
1468      * If the evaluation results in an {@code IOException} then the I/O
1469      * exception is wrapped in an {@link UncheckedIOException} that is then
1470      * thrown.
1471      *
1472      * <p> Resources in named modules are subject to the encapsulation rules
1473      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1474      * Additionally, and except for the special case where the resource has a
1475      * name ending with "{@code .class}", this method will only find resources in
1476      * packages of named modules when the package is {@link Module#isOpen(String)
1477      * opened} unconditionally (even if the caller of this method is in the
1478      * same module as the resource). </p>
1479      *
1480      * @implSpec The default implementation invokes {@link #getResources(String)
1481      * getResources} to find all the resources with the given name and returns
1482      * a stream with the elements in the enumeration as the source.
1483      *
1484      * @apiNote When overriding this method it is recommended that an
1485      * implementation ensures that any delegation is consistent with the {@link
1486      * #getResource(java.lang.String) getResource(String)} method. This should
1487      * ensure that the first element returned by the stream is the same
1488      * resource that the {@code getResource(String)} method would return.
1489      *
1490      * @param  name
1491      *         The resource name
1492      *
1493      * @return  A stream of resource {@link java.net.URL URL} objects. If no
1494      *          resources could  be found, the stream will be empty. Resources
1495      *          for which a {@code URL} cannot be constructed, are in a package
1496      *          that is not opened unconditionally, or access to the resource
1497      *          is denied by the security manager, will not be in the stream.
1498      *
1499      * @throws  NullPointerException If {@code name} is {@code null}
1500      *
1501      * @since  9
1502      */
1503     public Stream<URL> resources(String name) {
1504         Objects.requireNonNull(name);
1505         int characteristics = Spliterator.NONNULL | Spliterator.IMMUTABLE;
1506         Supplier<Spliterator<URL>> si = () -> {
1507             try {
1508                 return Spliterators.spliteratorUnknownSize(
1509                     getResources(name).asIterator(), characteristics);
1510             } catch (IOException e) {
1511                 throw new UncheckedIOException(e);
1512             }
1513         };
1514         return StreamSupport.stream(si, characteristics, false);
1515     }
1516 
1517     /**
1518      * Finds the resource with the given name. Class loader implementations
1519      * should override this method.
1520      *
1521      * <p> For resources in named modules then the method must implement the
1522      * rules for encapsulation specified in the {@code Module} {@link
1523      * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1524      * it must not find non-"{@code .class}" resources in packages of named
1525      * modules unless the package is {@link Module#isOpen(String) opened}
1526      * unconditionally. </p>
1527      *
1528      * @implSpec The default implementation returns {@code null}.
1529      *
1530      * @param  name
1531      *         The resource name
1532      *
1533      * @return  {@code URL} object for reading the resource; {@code null} if
1534      *          the resource could not be found, a {@code URL} could not be
1535      *          constructed to locate the resource, the resource is in a package
1536      *          that is not opened unconditionally, or access to the resource is
1537      *          denied by the security manager.
1538      *
1539      * @since  1.2
1540      * @revised 9
1541      * @spec JPMS
1542      */
1543     protected URL findResource(String name) {
1544         return null;
1545     }
1546 
1547     /**
1548      * Returns an enumeration of {@link java.net.URL URL} objects
1549      * representing all the resources with the given name. Class loader
1550      * implementations should override this method.
1551      *
1552      * <p> For resources in named modules then the method must implement the
1553      * rules for encapsulation specified in the {@code Module} {@link
1554      * Module#getResourceAsStream getResourceAsStream} method. Additionally,
1555      * it must not find non-"{@code .class}" resources in packages of named
1556      * modules unless the package is {@link Module#isOpen(String) opened}
1557      * unconditionally. </p>
1558      *
1559      * @implSpec The default implementation returns an enumeration that
1560      * contains no elements.
1561      *
1562      * @param  name
1563      *         The resource name
1564      *
1565      * @return  An enumeration of {@link java.net.URL URL} objects for
1566      *          the resource. If no resources could  be found, the enumeration
1567      *          will be empty. Resources for which a {@code URL} cannot be
1568      *          constructed, are in a package that is not opened unconditionally,
1569      *          or access to the resource is denied by the security manager,
1570      *          are not returned in the enumeration.
1571      *
1572      * @throws  IOException
1573      *          If I/O errors occur
1574      *
1575      * @since  1.2
1576      * @revised 9
1577      * @spec JPMS
1578      */
1579     protected Enumeration<URL> findResources(String name) throws IOException {
1580         return Collections.emptyEnumeration();
1581     }
1582 
1583     /**
1584      * Registers the caller as
1585      * {@linkplain #isRegisteredAsParallelCapable() parallel capable}.
1586      * The registration succeeds if and only if all of the following
1587      * conditions are met:
1588      * <ol>
1589      * <li> no instance of the caller has been created</li>
1590      * <li> all of the super classes (except class Object) of the caller are
1591      * registered as parallel capable</li>
1592      * </ol>
1593      * <p>Note that once a class loader is registered as parallel capable, there
1594      * is no way to change it back.</p>
1595      *
1596      * @return  {@code true} if the caller is successfully registered as
1597      *          parallel capable and {@code false} if otherwise.
1598      *
1599      * @see #isRegisteredAsParallelCapable()
1600      *
1601      * @since   1.7
1602      */
1603     @CallerSensitive
1604     protected static boolean registerAsParallelCapable() {
1605         Class<? extends ClassLoader> callerClass =
1606             Reflection.getCallerClass().asSubclass(ClassLoader.class);
1607         return ParallelLoaders.register(callerClass);
1608     }
1609 
1610     /**
1611      * Returns {@code true} if this class loader is registered as
1612      * {@linkplain #registerAsParallelCapable parallel capable}, otherwise
1613      * {@code false}.
1614      *
1615      * @return  {@code true} if this class loader is parallel capable,
1616      *          otherwise {@code false}.
1617      *
1618      * @see #registerAsParallelCapable()
1619      *
1620      * @since   9
1621      */
1622     public final boolean isRegisteredAsParallelCapable() {
1623         return ParallelLoaders.isRegistered(this.getClass());
1624     }
1625 
1626     /**
1627      * Find a resource of the specified name from the search path used to load
1628      * classes.  This method locates the resource through the system class
1629      * loader (see {@link #getSystemClassLoader()}).
1630      *
1631      * <p> Resources in named modules are subject to the encapsulation rules
1632      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1633      * Additionally, and except for the special case where the resource has a
1634      * name ending with "{@code .class}", this method will only find resources in
1635      * packages of named modules when the package is {@link Module#isOpen(String)
1636      * opened} unconditionally. </p>
1637      *
1638      * @param  name
1639      *         The resource name
1640      *
1641      * @return  A {@link java.net.URL URL} to the resource; {@code
1642      *          null} if the resource could not be found, a URL could not be
1643      *          constructed to locate the resource, the resource is in a package
1644      *          that is not opened unconditionally or access to the resource is
1645      *          denied by the security manager.
1646      *
1647      * @since  1.1
1648      * @revised 9
1649      * @spec JPMS
1650      */
1651     public static URL getSystemResource(String name) {
1652         return getSystemClassLoader().getResource(name);
1653     }
1654 
1655     /**
1656      * Finds all resources of the specified name from the search path used to
1657      * load classes.  The resources thus found are returned as an
1658      * {@link java.util.Enumeration Enumeration} of {@link
1659      * java.net.URL URL} objects.
1660      *
1661      * <p> The search order is described in the documentation for {@link
1662      * #getSystemResource(String)}.  </p>
1663      *
1664      * <p> Resources in named modules are subject to the encapsulation rules
1665      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1666      * Additionally, and except for the special case where the resource has a
1667      * name ending with "{@code .class}", this method will only find resources in
1668      * packages of named modules when the package is {@link Module#isOpen(String)
1669      * opened} unconditionally. </p>
1670      *
1671      * @param  name
1672      *         The resource name
1673      *
1674      * @return  An enumeration of {@link java.net.URL URL} objects for
1675      *          the resource. If no resources could  be found, the enumeration
1676      *          will be empty. Resources for which a {@code URL} cannot be
1677      *          constructed, are in a package that is not opened unconditionally,
1678      *          or access to the resource is denied by the security manager,
1679      *          are not returned in the enumeration.
1680      *
1681      * @throws  IOException
1682      *          If I/O errors occur
1683      *
1684      * @since  1.2
1685      * @revised 9
1686      * @spec JPMS
1687      */
1688     public static Enumeration<URL> getSystemResources(String name)
1689         throws IOException
1690     {
1691         return getSystemClassLoader().getResources(name);
1692     }
1693 
1694     /**
1695      * Returns an input stream for reading the specified resource.
1696      *
1697      * <p> The search order is described in the documentation for {@link
1698      * #getResource(String)}.  </p>
1699      *
1700      * <p> Resources in named modules are subject to the encapsulation rules
1701      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1702      * Additionally, and except for the special case where the resource has a
1703      * name ending with "{@code .class}", this method will only find resources in
1704      * packages of named modules when the package is {@link Module#isOpen(String)
1705      * opened} unconditionally. </p>
1706      *
1707      * @param  name
1708      *         The resource name
1709      *
1710      * @return  An input stream for reading the resource; {@code null} if the
1711      *          resource could not be found, the resource is in a package that
1712      *          is not opened unconditionally, or access to the resource is
1713      *          denied by the security manager.
1714      *
1715      * @throws  NullPointerException If {@code name} is {@code null}
1716      *
1717      * @since  1.1
1718      * @revised 9
1719      * @spec JPMS
1720      */
1721     public InputStream getResourceAsStream(String name) {
1722         Objects.requireNonNull(name);
1723         URL url = getResource(name);
1724         try {
1725             return url != null ? url.openStream() : null;
1726         } catch (IOException e) {
1727             return null;
1728         }
1729     }
1730 
1731     /**
1732      * Open for reading, a resource of the specified name from the search path
1733      * used to load classes.  This method locates the resource through the
1734      * system class loader (see {@link #getSystemClassLoader()}).
1735      *
1736      * <p> Resources in named modules are subject to the encapsulation rules
1737      * specified by {@link Module#getResourceAsStream Module.getResourceAsStream}.
1738      * Additionally, and except for the special case where the resource has a
1739      * name ending with "{@code .class}", this method will only find resources in
1740      * packages of named modules when the package is {@link Module#isOpen(String)
1741      * opened} unconditionally. </p>
1742      *
1743      * @param  name
1744      *         The resource name
1745      *
1746      * @return  An input stream for reading the resource; {@code null} if the
1747      *          resource could not be found, the resource is in a package that
1748      *          is not opened unconditionally, or access to the resource is
1749      *          denied by the security manager.
1750      *
1751      * @since  1.1
1752      * @revised 9
1753      * @spec JPMS
1754      */
1755     public static InputStream getSystemResourceAsStream(String name) {
1756         URL url = getSystemResource(name);
1757         try {
1758             return url != null ? url.openStream() : null;
1759         } catch (IOException e) {
1760             return null;
1761         }
1762     }
1763 
1764 
1765     // -- Hierarchy --
1766 
1767     /**
1768      * Returns the parent class loader for delegation. Some implementations may
1769      * use {@code null} to represent the bootstrap class loader. This method
1770      * will return {@code null} in such implementations if this class loader's
1771      * parent is the bootstrap class loader.
1772      *
1773      * @return  The parent {@code ClassLoader}
1774      *
1775      * @throws  SecurityException
1776      *          If a security manager is present, and the caller's class loader
1777      *          is not {@code null} and is not an ancestor of this class loader,
1778      *          and the caller does not have the
1779      *          {@link RuntimePermission}{@code ("getClassLoader")}
1780      *
1781      * @since  1.2
1782      */
1783     @CallerSensitive
1784     public final ClassLoader getParent() {
1785         if (parent == null)
1786             return null;
1787         SecurityManager sm = System.getSecurityManager();
1788         if (sm != null) {
1789             // Check access to the parent class loader
1790             // If the caller's class loader is same as this class loader,
1791             // permission check is performed.
1792             checkClassLoaderPermission(parent, Reflection.getCallerClass());
1793         }
1794         return parent;
1795     }
1796 
1797     /**
1798      * Returns the unnamed {@code Module} for this class loader.
1799      *
1800      * @return The unnamed Module for this class loader
1801      *
1802      * @see Module#isNamed()
1803      * @since 9
1804      * @spec JPMS
1805      */
1806     public final Module getUnnamedModule() {
1807         return unnamedModule;
1808     }
1809 
1810     /**
1811      * Returns the platform class loader.  All
1812      * <a href="#builtinLoaders">platform classes</a> are visible to
1813      * the platform class loader.
1814      *
1815      * @implNote The name of the builtin platform class loader is
1816      * {@code "platform"}.
1817      *
1818      * @return  The platform {@code ClassLoader}.
1819      *
1820      * @throws  SecurityException
1821      *          If a security manager is present, and the caller's class loader is
1822      *          not {@code null}, and the caller's class loader is not the same
1823      *          as or an ancestor of the platform class loader,
1824      *          and the caller does not have the
1825      *          {@link RuntimePermission}{@code ("getClassLoader")}
1826      *
1827      * @since 9
1828      * @spec JPMS
1829      */
1830     @CallerSensitive
1831     public static ClassLoader getPlatformClassLoader() {
1832         SecurityManager sm = System.getSecurityManager();
1833         ClassLoader loader = getBuiltinPlatformClassLoader();
1834         if (sm != null) {
1835             checkClassLoaderPermission(loader, Reflection.getCallerClass());
1836         }
1837         return loader;
1838     }
1839 
1840     /**
1841      * Returns the system class loader.  This is the default
1842      * delegation parent for new {@code ClassLoader} instances, and is
1843      * typically the class loader used to start the application.
1844      *
1845      * <p> This method is first invoked early in the runtime's startup
1846      * sequence, at which point it creates the system class loader. This
1847      * class loader will be the context class loader for the main application
1848      * thread (for example, the thread that invokes the {@code main} method of
1849      * the main class).
1850      *
1851      * <p> The default system class loader is an implementation-dependent
1852      * instance of this class.
1853      *
1854      * <p> If the system property "{@systemProperty java.system.class.loader}"
1855      * is defined when this method is first invoked then the value of that
1856      * property is taken to be the name of a class that will be returned as the
1857      * system class loader. The class is loaded using the default system class
1858      * loader and must define a public constructor that takes a single parameter
1859      * of type {@code ClassLoader} which is used as the delegation parent. An
1860      * instance is then created using this constructor with the default system
1861      * class loader as the parameter.  The resulting class loader is defined
1862      * to be the system class loader. During construction, the class loader
1863      * should take great care to avoid calling {@code getSystemClassLoader()}.
1864      * If circular initialization of the system class loader is detected then
1865      * an {@code IllegalStateException} is thrown.
1866      *
1867      * @implNote The system property to override the system class loader is not
1868      * examined until the VM is almost fully initialized. Code that executes
1869      * this method during startup should take care not to cache the return
1870      * value until the system is fully initialized.
1871      *
1872      * <p> The name of the built-in system class loader is {@code "app"}.
1873      * The system property "{@code java.class.path}" is read during early
1874      * initialization of the VM to determine the class path.
1875      * An empty value of "{@code java.class.path}" property is interpreted
1876      * differently depending on whether the initial module (the module
1877      * containing the main class) is named or unnamed:
1878      * If named, the built-in system class loader will have no class path and
1879      * will search for classes and resources using the application module path;
1880      * otherwise, if unnamed, it will set the class path to the current
1881      * working directory.
1882      *
1883      * <p> JAR files on the class path may contain a {@code Class-Path} manifest
1884      * attribute to specify dependent JAR files to be included in the class path.
1885      * {@code Class-Path} entries must meet certain conditions for validity (see
1886      * the <a href="{@docRoot}/../specs/jar/jar.html#class-path-attribute">
1887      * JAR File Specification</a> for details).  Invalid {@code Class-Path}
1888      * entries are ignored.  For debugging purposes, ignored entries can be
1889      * printed to the console if the
1890      * {@systemProperty jdk.net.URLClassPath.showIgnoredClassPathEntries} system
1891      * property is set to {@code true}.
1892      *
1893      * @return  The system {@code ClassLoader}
1894      *
1895      * @throws  SecurityException
1896      *          If a security manager is present, and the caller's class loader
1897      *          is not {@code null} and is not the same as or an ancestor of the
1898      *          system class loader, and the caller does not have the
1899      *          {@link RuntimePermission}{@code ("getClassLoader")}
1900      *
1901      * @throws  IllegalStateException
1902      *          If invoked recursively during the construction of the class
1903      *          loader specified by the "{@code java.system.class.loader}"
1904      *          property.
1905      *
1906      * @throws  Error
1907      *          If the system property "{@code java.system.class.loader}"
1908      *          is defined but the named class could not be loaded, the
1909      *          provider class does not define the required constructor, or an
1910      *          exception is thrown by that constructor when it is invoked. The
1911      *          underlying cause of the error can be retrieved via the
1912      *          {@link Throwable#getCause()} method.
1913      *
1914      * @revised  1.4
1915      * @revised 9
1916      * @spec JPMS
1917      */
1918     @CallerSensitive
1919     public static ClassLoader getSystemClassLoader() {
1920         switch (VM.initLevel()) {
1921             case 0:
1922             case 1:
1923             case 2:
1924                 // the system class loader is the built-in app class loader during startup
1925                 return getBuiltinAppClassLoader();
1926             case 3:
1927                 String msg = "getSystemClassLoader cannot be called during the system class loader instantiation";
1928                 throw new IllegalStateException(msg);
1929             default:
1930                 // system fully initialized
1931                 assert VM.isBooted() && scl != null;
1932                 SecurityManager sm = System.getSecurityManager();
1933                 if (sm != null) {
1934                     checkClassLoaderPermission(scl, Reflection.getCallerClass());
1935                 }
1936                 return scl;
1937         }
1938     }
1939 
1940     static ClassLoader getBuiltinPlatformClassLoader() {
1941         return ClassLoaders.platformClassLoader();
1942     }
1943 
1944     static ClassLoader getBuiltinAppClassLoader() {
1945         return ClassLoaders.appClassLoader();
1946     }
1947 
1948     /*
1949      * Initialize the system class loader that may be a custom class on the
1950      * application class path or application module path.
1951      *
1952      * @see java.lang.System#initPhase3
1953      */
1954     static synchronized ClassLoader initSystemClassLoader() {
1955         if (VM.initLevel() != 3) {
1956             throw new InternalError("system class loader cannot be set at initLevel " +
1957                                     VM.initLevel());
1958         }
1959 
1960         // detect recursive initialization
1961         if (scl != null) {
1962             throw new IllegalStateException("recursive invocation");
1963         }
1964 
1965         ClassLoader builtinLoader = getBuiltinAppClassLoader();
1966 
1967         // All are privileged frames.  No need to call doPrivileged.
1968         String cn = System.getProperty("java.system.class.loader");
1969         if (cn != null) {
1970             try {
1971                 // custom class loader is only supported to be loaded from unnamed module
1972                 Constructor<?> ctor = Class.forName(cn, false, builtinLoader)
1973                                            .getDeclaredConstructor(ClassLoader.class);
1974                 scl = (ClassLoader) ctor.newInstance(builtinLoader);
1975             } catch (Exception e) {
1976                 Throwable cause = e;
1977                 if (e instanceof InvocationTargetException) {
1978                     cause = e.getCause();
1979                     if (cause instanceof Error) {
1980                         throw (Error) cause;
1981                     }
1982                 }
1983                 if (cause instanceof RuntimeException) {
1984                     throw (RuntimeException) cause;
1985                 }
1986                 throw new Error(cause.getMessage(), cause);
1987             }
1988         } else {
1989             scl = builtinLoader;
1990         }
1991         return scl;
1992     }
1993 
1994     // Returns true if the specified class loader can be found in this class
1995     // loader's delegation chain.
1996     boolean isAncestor(ClassLoader cl) {
1997         ClassLoader acl = this;
1998         do {
1999             acl = acl.parent;
2000             if (cl == acl) {
2001                 return true;
2002             }
2003         } while (acl != null);
2004         return false;
2005     }
2006 
2007     // Tests if class loader access requires "getClassLoader" permission
2008     // check.  A class loader 'from' can access class loader 'to' if
2009     // class loader 'from' is same as class loader 'to' or an ancestor
2010     // of 'to'.  The class loader in a system domain can access
2011     // any class loader.
2012     private static boolean needsClassLoaderPermissionCheck(ClassLoader from,
2013                                                            ClassLoader to)
2014     {
2015         if (from == to)
2016             return false;
2017 
2018         if (from == null)
2019             return false;
2020 
2021         return !to.isAncestor(from);
2022     }
2023 
2024     // Returns the class's class loader, or null if none.
2025     static ClassLoader getClassLoader(Class<?> caller) {
2026         // This can be null if the VM is requesting it
2027         if (caller == null) {
2028             return null;
2029         }
2030         // Circumvent security check since this is package-private
2031         return caller.getClassLoader0();
2032     }
2033 
2034     /*
2035      * Checks RuntimePermission("getClassLoader") permission
2036      * if caller's class loader is not null and caller's class loader
2037      * is not the same as or an ancestor of the given cl argument.
2038      */
2039     static void checkClassLoaderPermission(ClassLoader cl, Class<?> caller) {
2040         SecurityManager sm = System.getSecurityManager();
2041         if (sm != null) {
2042             // caller can be null if the VM is requesting it
2043             ClassLoader ccl = getClassLoader(caller);
2044             if (needsClassLoaderPermissionCheck(ccl, cl)) {
2045                 sm.checkPermission(SecurityConstants.GET_CLASSLOADER_PERMISSION);
2046             }
2047         }
2048     }
2049 
2050     // The system class loader
2051     // @GuardedBy("ClassLoader.class")
2052     private static volatile ClassLoader scl;
2053 
2054     // -- Package --
2055 
2056     /**
2057      * Define a Package of the given Class object.
2058      *
2059      * If the given class represents an array type, a primitive type or void,
2060      * this method returns {@code null}.
2061      *
2062      * This method does not throw IllegalArgumentException.
2063      */
2064     Package definePackage(Class<?> c) {
2065         if (c.isPrimitive() || c.isArray()) {
2066             return null;
2067         }
2068 
2069         return definePackage(c.getPackageName(), c.getModule());
2070     }
2071 
2072     /**
2073      * Defines a Package of the given name and module
2074      *
2075      * This method does not throw IllegalArgumentException.
2076      *
2077      * @param name package name
2078      * @param m    module
2079      */
2080     Package definePackage(String name, Module m) {
2081         if (name.isEmpty() && m.isNamed()) {
2082             throw new InternalError("unnamed package in  " + m);
2083         }
2084 
2085         // check if Package object is already defined
2086         NamedPackage pkg = packages.get(name);
2087         if (pkg instanceof Package)
2088             return (Package)pkg;
2089 
2090         return (Package)packages.compute(name, (n, p) -> toPackage(n, p, m));
2091     }
2092 
2093     /*
2094      * Returns a Package object for the named package
2095      */
2096     private Package toPackage(String name, NamedPackage p, Module m) {
2097         // define Package object if the named package is not yet defined
2098         if (p == null)
2099             return NamedPackage.toPackage(name, m);
2100 
2101         // otherwise, replace the NamedPackage object with Package object
2102         if (p instanceof Package)
2103             return (Package)p;
2104 
2105         return NamedPackage.toPackage(p.packageName(), p.module());
2106     }
2107 
2108     /**
2109      * Defines a package by <a href="#binary-name">name</a> in this {@code ClassLoader}.
2110      * <p>
2111      * <a href="#binary-name">Package names</a> must be unique within a class loader and
2112      * cannot be redefined or changed once created.
2113      * <p>
2114      * If a class loader wishes to define a package with specific properties,
2115      * such as version information, then the class loader should call this
2116      * {@code definePackage} method before calling {@code defineClass}.
2117      * Otherwise, the
2118      * {@link #defineClass(String, byte[], int, int, ProtectionDomain) defineClass}
2119      * method will define a package in this class loader corresponding to the package
2120      * of the newly defined class; the properties of this defined package are
2121      * specified by {@link Package}.
2122      *
2123      * @apiNote
2124      * A class loader that wishes to define a package for classes in a JAR
2125      * typically uses the specification and implementation titles, versions, and
2126      * vendors from the JAR's manifest. If the package is specified as
2127      * {@linkplain java.util.jar.Attributes.Name#SEALED sealed} in the JAR's manifest,
2128      * the {@code URL} of the JAR file is typically used as the {@code sealBase}.
2129      * If classes of package {@code 'p'} defined by this class loader
2130      * are loaded from multiple JARs, the {@code Package} object may contain
2131      * different information depending on the first class of package {@code 'p'}
2132      * defined and which JAR's manifest is read first to explicitly define
2133      * package {@code 'p'}.
2134      *
2135      * <p> It is strongly recommended that a class loader does not call this
2136      * method to explicitly define packages in <em>named modules</em>; instead,
2137      * the package will be automatically defined when a class is {@linkplain
2138      * #defineClass(String, byte[], int, int, ProtectionDomain) being defined}.
2139      * If it is desirable to define {@code Package} explicitly, it should ensure
2140      * that all packages in a named module are defined with the properties
2141      * specified by {@link Package}.  Otherwise, some {@code Package} objects
2142      * in a named module may be for example sealed with different seal base.
2143      *
2144      * @param  name
2145      *         The <a href="#binary-name">package name</a>
2146      *
2147      * @param  specTitle
2148      *         The specification title
2149      *
2150      * @param  specVersion
2151      *         The specification version
2152      *
2153      * @param  specVendor
2154      *         The specification vendor
2155      *
2156      * @param  implTitle
2157      *         The implementation title
2158      *
2159      * @param  implVersion
2160      *         The implementation version
2161      *
2162      * @param  implVendor
2163      *         The implementation vendor
2164      *
2165      * @param  sealBase
2166      *         If not {@code null}, then this package is sealed with
2167      *         respect to the given code source {@link java.net.URL URL}
2168      *         object.  Otherwise, the package is not sealed.
2169      *
2170      * @return  The newly defined {@code Package} object
2171      *
2172      * @throws  NullPointerException
2173      *          if {@code name} is {@code null}.
2174      *
2175      * @throws  IllegalArgumentException
2176      *          if a package of the given {@code name} is already
2177      *          defined by this class loader
2178      *
2179      *
2180      * @since  1.2
2181      * @revised 9
2182      * @spec JPMS
2183      *
2184      * @jvms 5.3 Creation and Loading
2185      * @see <a href="{@docRoot}/../specs/jar/jar.html#package-sealing">
2186      *      The JAR File Specification: Package Sealing</a>
2187      */
2188     protected Package definePackage(String name, String specTitle,
2189                                     String specVersion, String specVendor,
2190                                     String implTitle, String implVersion,
2191                                     String implVendor, URL sealBase)
2192     {
2193         Objects.requireNonNull(name);
2194 
2195         // definePackage is not final and may be overridden by custom class loader
2196         Package p = new Package(name, specTitle, specVersion, specVendor,
2197                                 implTitle, implVersion, implVendor,
2198                                 sealBase, this);
2199 
2200         if (packages.putIfAbsent(name, p) != null)
2201             throw new IllegalArgumentException(name);
2202 
2203         return p;
2204     }
2205 
2206     /**
2207      * Returns a {@code Package} of the given <a href="#binary-name">name</a> that
2208      * has been defined by this class loader.
2209      *
2210      * @param  name The <a href="#binary-name">package name</a>
2211      *
2212      * @return The {@code Package} of the given name that has been defined
2213      *         by this class loader, or {@code null} if not found
2214      *
2215      * @throws  NullPointerException
2216      *          if {@code name} is {@code null}.
2217      *
2218      * @jvms 5.3 Creation and Loading
2219      *
2220      * @since  9
2221      * @spec JPMS
2222      */
2223     public final Package getDefinedPackage(String name) {
2224         Objects.requireNonNull(name, "name cannot be null");
2225 
2226         NamedPackage p = packages.get(name);
2227         if (p == null)
2228             return null;
2229 
2230         return definePackage(name, p.module());
2231     }
2232 
2233     /**
2234      * Returns all of the {@code Package}s that have been defined by
2235      * this class loader.  The returned array has no duplicated {@code Package}s
2236      * of the same name.
2237      *
2238      * @apiNote This method returns an array rather than a {@code Set} or {@code Stream}
2239      *          for consistency with the existing {@link #getPackages} method.
2240      *
2241      * @return The array of {@code Package} objects that have been defined by
2242      *         this class loader; or an zero length array if no package has been
2243      *         defined by this class loader.
2244      *
2245      * @jvms 5.3 Creation and Loading
2246      *
2247      * @since  9
2248      * @spec JPMS
2249      */
2250     public final Package[] getDefinedPackages() {
2251         return packages().toArray(Package[]::new);
2252     }
2253 
2254     /**
2255      * Finds a package by <a href="#binary-name">name</a> in this class loader and its ancestors.
2256      * <p>
2257      * If this class loader defines a {@code Package} of the given name,
2258      * the {@code Package} is returned. Otherwise, the ancestors of
2259      * this class loader are searched recursively (parent by parent)
2260      * for a {@code Package} of the given name.
2261      *
2262      * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2263      * may delegate to the application class loader but the application class
2264      * loader is not its ancestor.  When invoked on the platform class loader,
2265      * this method  will not find packages defined to the application
2266      * class loader.
2267      *
2268      * @param  name
2269      *         The <a href="#binary-name">package name</a>
2270      *
2271      * @return The {@code Package} of the given name that has been defined by
2272      *         this class loader or its ancestors, or {@code null} if not found.
2273      *
2274      * @throws  NullPointerException
2275      *          if {@code name} is {@code null}.
2276      *
2277      * @deprecated
2278      * If multiple class loaders delegate to each other and define classes
2279      * with the same package name, and one such loader relies on the lookup
2280      * behavior of {@code getPackage} to return a {@code Package} from
2281      * a parent loader, then the properties exposed by the {@code Package}
2282      * may not be as expected in the rest of the program.
2283      * For example, the {@code Package} will only expose annotations from the
2284      * {@code package-info.class} file defined by the parent loader, even if
2285      * annotations exist in a {@code package-info.class} file defined by
2286      * a child loader.  A more robust approach is to use the
2287      * {@link ClassLoader#getDefinedPackage} method which returns
2288      * a {@code Package} for the specified class loader.
2289      *
2290      * @see ClassLoader#getDefinedPackage(String)
2291      *
2292      * @since  1.2
2293      * @revised 9
2294      * @spec JPMS
2295      */
2296     @Deprecated(since="9")
2297     protected Package getPackage(String name) {
2298         Package pkg = getDefinedPackage(name);
2299         if (pkg == null) {
2300             if (parent != null) {
2301                 pkg = parent.getPackage(name);
2302             } else {
2303                 pkg = BootLoader.getDefinedPackage(name);
2304             }
2305         }
2306         return pkg;
2307     }
2308 
2309     /**
2310      * Returns all of the {@code Package}s that have been defined by
2311      * this class loader and its ancestors.  The returned array may contain
2312      * more than one {@code Package} object of the same package name, each
2313      * defined by a different class loader in the class loader hierarchy.
2314      *
2315      * @apiNote The {@link #getPlatformClassLoader() platform class loader}
2316      * may delegate to the application class loader. In other words,
2317      * packages in modules defined to the application class loader may be
2318      * visible to the platform class loader.  On the other hand,
2319      * the application class loader is not its ancestor and hence
2320      * when invoked on the platform class loader, this method will not
2321      * return any packages defined to the application class loader.
2322      *
2323      * @return  The array of {@code Package} objects that have been defined by
2324      *          this class loader and its ancestors
2325      *
2326      * @see ClassLoader#getDefinedPackages()
2327      *
2328      * @since  1.2
2329      * @revised 9
2330      * @spec JPMS
2331      */
2332     protected Package[] getPackages() {
2333         Stream<Package> pkgs = packages();
2334         ClassLoader ld = parent;
2335         while (ld != null) {
2336             pkgs = Stream.concat(ld.packages(), pkgs);
2337             ld = ld.parent;
2338         }
2339         return Stream.concat(BootLoader.packages(), pkgs)
2340                      .toArray(Package[]::new);
2341     }
2342 
2343 
2344 
2345     // package-private
2346 
2347     /**
2348      * Returns a stream of Packages defined in this class loader
2349      */
2350     Stream<Package> packages() {
2351         return packages.values().stream()
2352                        .map(p -> definePackage(p.packageName(), p.module()));
2353     }
2354 
2355     // -- Native library access --
2356 
2357     /**
2358      * Returns the absolute path name of a native library.  The VM invokes this
2359      * method to locate the native libraries that belong to classes loaded with
2360      * this class loader. If this method returns {@code null}, the VM
2361      * searches the library along the path specified as the
2362      * "{@code java.library.path}" property.
2363      *
2364      * @param  libname
2365      *         The library name
2366      *
2367      * @return  The absolute path of the native library
2368      *
2369      * @see  System#loadLibrary(String)
2370      * @see  System#mapLibraryName(String)
2371      *
2372      * @since  1.2
2373      */
2374     protected String findLibrary(String libname) {
2375         return null;
2376     }
2377 
2378     private final NativeLibraries libraries = new NativeLibraries(this);
2379 
2380     // Invoked in the java.lang.Runtime class to implement load and loadLibrary.
2381     static NativeLibrary loadLibrary(Class<?> fromClass, File file) {
2382         ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2383         NativeLibraries libs = loader != null ? loader.libraries : BootLoader.getNativeLibraries();
2384         NativeLibrary nl = libs.loadLibrary(fromClass, file);
2385         if (nl != null) {
2386             return nl;
2387         }
2388         throw new UnsatisfiedLinkError("Can't load library: " + file);
2389     }
2390     static NativeLibrary loadLibrary(Class<?> fromClass, String name) {
2391         ClassLoader loader = (fromClass == null) ? null : fromClass.getClassLoader();
2392         if (loader == null) {
2393             NativeLibrary nl = BootLoader.getNativeLibraries().loadLibrary(fromClass, name);
2394             if (nl != null) {
2395                 return nl;
2396             }
2397             throw new UnsatisfiedLinkError("no " + name +
2398                     " in java.library.path: " + StaticProperty.sunBootLibraryPath());
2399         }
2400 
2401         NativeLibraries libs = loader.libraries;
2402         // First load from the file returned from ClassLoader::findLibrary, if found.
2403         String libfilename = loader.findLibrary(name);
2404         if (libfilename != null) {
2405             File libfile = new File(libfilename);
2406             if (!libfile.isAbsolute()) {
2407                 throw new UnsatisfiedLinkError(
2408                         "ClassLoader.findLibrary failed to return an absolute path: " + libfilename);
2409             }
2410             NativeLibrary nl = libs.loadLibrary(fromClass, libfile);
2411             if (nl != null) {
2412                 return nl;
2413             }
2414             throw new UnsatisfiedLinkError("Can't load " + libfilename);
2415         }
2416         // Then load from system library path and java library path
2417         NativeLibrary nl = libs.loadLibrary(fromClass, name);
2418         if (nl != null) {
2419             return nl;
2420         }
2421 
2422         // Oops, it failed
2423         throw new UnsatisfiedLinkError("no " + name +
2424                 " in java.library.path: " + StaticProperty.javaLibraryPath());
2425     }
2426 
2427     /*
2428      * Invoked in the VM class linking code.
2429      */
2430     private static long findNative(ClassLoader loader, String entryName) {
2431         if (loader == null) {
2432             return BootLoader.getNativeLibraries().lookup(entryName);
2433         } else {
2434             return loader.libraries.lookup(entryName);
2435         }
2436     }
2437 
2438     // -- Assertion management --
2439 
2440     final Object assertionLock;
2441 
2442     // The default toggle for assertion checking.
2443     // @GuardedBy("assertionLock")
2444     private boolean defaultAssertionStatus = false;
2445 
2446     // Maps String packageName to Boolean package default assertion status Note
2447     // that the default package is placed under a null map key.  If this field
2448     // is null then we are delegating assertion status queries to the VM, i.e.,
2449     // none of this ClassLoader's assertion status modification methods have
2450     // been invoked.
2451     // @GuardedBy("assertionLock")
2452     private Map<String, Boolean> packageAssertionStatus = null;
2453 
2454     // Maps String fullyQualifiedClassName to Boolean assertionStatus If this
2455     // field is null then we are delegating assertion status queries to the VM,
2456     // i.e., none of this ClassLoader's assertion status modification methods
2457     // have been invoked.
2458     // @GuardedBy("assertionLock")
2459     Map<String, Boolean> classAssertionStatus = null;
2460 
2461     /**
2462      * Sets the default assertion status for this class loader.  This setting
2463      * determines whether classes loaded by this class loader and initialized
2464      * in the future will have assertions enabled or disabled by default.
2465      * This setting may be overridden on a per-package or per-class basis by
2466      * invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
2467      * #setClassAssertionStatus(String, boolean)}.
2468      *
2469      * @param  enabled
2470      *         {@code true} if classes loaded by this class loader will
2471      *         henceforth have assertions enabled by default, {@code false}
2472      *         if they will have assertions disabled by default.
2473      *
2474      * @since  1.4
2475      */
2476     public void setDefaultAssertionStatus(boolean enabled) {
2477         synchronized (assertionLock) {
2478             if (classAssertionStatus == null)
2479                 initializeJavaAssertionMaps();
2480 
2481             defaultAssertionStatus = enabled;
2482         }
2483     }
2484 
2485     /**
2486      * Sets the package default assertion status for the named package.  The
2487      * package default assertion status determines the assertion status for
2488      * classes initialized in the future that belong to the named package or
2489      * any of its "subpackages".
2490      *
2491      * <p> A subpackage of a package named p is any package whose name begins
2492      * with "{@code p.}".  For example, {@code javax.swing.text} is a
2493      * subpackage of {@code javax.swing}, and both {@code java.util} and
2494      * {@code java.lang.reflect} are subpackages of {@code java}.
2495      *
2496      * <p> In the event that multiple package defaults apply to a given class,
2497      * the package default pertaining to the most specific package takes
2498      * precedence over the others.  For example, if {@code javax.lang} and
2499      * {@code javax.lang.reflect} both have package defaults associated with
2500      * them, the latter package default applies to classes in
2501      * {@code javax.lang.reflect}.
2502      *
2503      * <p> Package defaults take precedence over the class loader's default
2504      * assertion status, and may be overridden on a per-class basis by invoking
2505      * {@link #setClassAssertionStatus(String, boolean)}.  </p>
2506      *
2507      * @param  packageName
2508      *         The name of the package whose package default assertion status
2509      *         is to be set. A {@code null} value indicates the unnamed
2510      *         package that is "current"
2511      *         (see section 7.4.2 of
2512      *         <cite>The Java&trade; Language Specification</cite>.)
2513      *
2514      * @param  enabled
2515      *         {@code true} if classes loaded by this classloader and
2516      *         belonging to the named package or any of its subpackages will
2517      *         have assertions enabled by default, {@code false} if they will
2518      *         have assertions disabled by default.
2519      *
2520      * @since  1.4
2521      */
2522     public void setPackageAssertionStatus(String packageName,
2523                                           boolean enabled) {
2524         synchronized (assertionLock) {
2525             if (packageAssertionStatus == null)
2526                 initializeJavaAssertionMaps();
2527 
2528             packageAssertionStatus.put(packageName, enabled);
2529         }
2530     }
2531 
2532     /**
2533      * Sets the desired assertion status for the named top-level class in this
2534      * class loader and any nested classes contained therein.  This setting
2535      * takes precedence over the class loader's default assertion status, and
2536      * over any applicable per-package default.  This method has no effect if
2537      * the named class has already been initialized.  (Once a class is
2538      * initialized, its assertion status cannot change.)
2539      *
2540      * <p> If the named class is not a top-level class, this invocation will
2541      * have no effect on the actual assertion status of any class. </p>
2542      *
2543      * @param  className
2544      *         The fully qualified class name of the top-level class whose
2545      *         assertion status is to be set.
2546      *
2547      * @param  enabled
2548      *         {@code true} if the named class is to have assertions
2549      *         enabled when (and if) it is initialized, {@code false} if the
2550      *         class is to have assertions disabled.
2551      *
2552      * @since  1.4
2553      */
2554     public void setClassAssertionStatus(String className, boolean enabled) {
2555         synchronized (assertionLock) {
2556             if (classAssertionStatus == null)
2557                 initializeJavaAssertionMaps();
2558 
2559             classAssertionStatus.put(className, enabled);
2560         }
2561     }
2562 
2563     /**
2564      * Sets the default assertion status for this class loader to
2565      * {@code false} and discards any package defaults or class assertion
2566      * status settings associated with the class loader.  This method is
2567      * provided so that class loaders can be made to ignore any command line or
2568      * persistent assertion status settings and "start with a clean slate."
2569      *
2570      * @since  1.4
2571      */
2572     public void clearAssertionStatus() {
2573         /*
2574          * Whether or not "Java assertion maps" are initialized, set
2575          * them to empty maps, effectively ignoring any present settings.
2576          */
2577         synchronized (assertionLock) {
2578             classAssertionStatus = new HashMap<>();
2579             packageAssertionStatus = new HashMap<>();
2580             defaultAssertionStatus = false;
2581         }
2582     }
2583 
2584     /**
2585      * Returns the assertion status that would be assigned to the specified
2586      * class if it were to be initialized at the time this method is invoked.
2587      * If the named class has had its assertion status set, the most recent
2588      * setting will be returned; otherwise, if any package default assertion
2589      * status pertains to this class, the most recent setting for the most
2590      * specific pertinent package default assertion status is returned;
2591      * otherwise, this class loader's default assertion status is returned.
2592      * </p>
2593      *
2594      * @param  className
2595      *         The fully qualified class name of the class whose desired
2596      *         assertion status is being queried.
2597      *
2598      * @return  The desired assertion status of the specified class.
2599      *
2600      * @see  #setClassAssertionStatus(String, boolean)
2601      * @see  #setPackageAssertionStatus(String, boolean)
2602      * @see  #setDefaultAssertionStatus(boolean)
2603      *
2604      * @since  1.4
2605      */
2606     boolean desiredAssertionStatus(String className) {
2607         synchronized (assertionLock) {
2608             // assert classAssertionStatus   != null;
2609             // assert packageAssertionStatus != null;
2610 
2611             // Check for a class entry
2612             Boolean result = classAssertionStatus.get(className);
2613             if (result != null)
2614                 return result.booleanValue();
2615 
2616             // Check for most specific package entry
2617             int dotIndex = className.lastIndexOf('.');
2618             if (dotIndex < 0) { // default package
2619                 result = packageAssertionStatus.get(null);
2620                 if (result != null)
2621                     return result.booleanValue();
2622             }
2623             while(dotIndex > 0) {
2624                 className = className.substring(0, dotIndex);
2625                 result = packageAssertionStatus.get(className);
2626                 if (result != null)
2627                     return result.booleanValue();
2628                 dotIndex = className.lastIndexOf('.', dotIndex-1);
2629             }
2630 
2631             // Return the classloader default
2632             return defaultAssertionStatus;
2633         }
2634     }
2635 
2636     // Set up the assertions with information provided by the VM.
2637     // Note: Should only be called inside a synchronized block
2638     private void initializeJavaAssertionMaps() {
2639         // assert Thread.holdsLock(assertionLock);
2640 
2641         classAssertionStatus = new HashMap<>();
2642         packageAssertionStatus = new HashMap<>();
2643         AssertionStatusDirectives directives = retrieveDirectives();
2644 
2645         for(int i = 0; i < directives.classes.length; i++)
2646             classAssertionStatus.put(directives.classes[i],
2647                                      directives.classEnabled[i]);
2648 
2649         for(int i = 0; i < directives.packages.length; i++)
2650             packageAssertionStatus.put(directives.packages[i],
2651                                        directives.packageEnabled[i]);
2652 
2653         defaultAssertionStatus = directives.deflt;
2654     }
2655 
2656     // Retrieves the assertion directives from the VM.
2657     private static native AssertionStatusDirectives retrieveDirectives();
2658 
2659 
2660     // -- Misc --
2661 
2662     /**
2663      * Returns the ConcurrentHashMap used as a storage for ClassLoaderValue(s)
2664      * associated with this ClassLoader, creating it if it doesn't already exist.
2665      */
2666     ConcurrentHashMap<?, ?> createOrGetClassLoaderValueMap() {
2667         ConcurrentHashMap<?, ?> map = classLoaderValueMap;
2668         if (map == null) {
2669             map = new ConcurrentHashMap<>();
2670             boolean set = trySetObjectField("classLoaderValueMap", map);
2671             if (!set) {
2672                 // beaten by someone else
2673                 map = classLoaderValueMap;
2674             }
2675         }
2676         return map;
2677     }
2678 
2679     // the storage for ClassLoaderValue(s) associated with this ClassLoader
2680     private volatile ConcurrentHashMap<?, ?> classLoaderValueMap;
2681 
2682     /**
2683      * Attempts to atomically set a volatile field in this object. Returns
2684      * {@code true} if not beaten by another thread. Avoids the use of
2685      * AtomicReferenceFieldUpdater in this class.
2686      */
2687     private boolean trySetObjectField(String name, Object obj) {
2688         Unsafe unsafe = Unsafe.getUnsafe();
2689         Class<?> k = ClassLoader.class;
2690         long offset;
2691         offset = unsafe.objectFieldOffset(k, name);
2692         return unsafe.compareAndSetReference(this, offset, null, obj);
2693     }
2694 }
2695 
2696 /*
2697  * A utility class that will enumerate over an array of enumerations.
2698  */
2699 final class CompoundEnumeration<E> implements Enumeration<E> {
2700     private final Enumeration<E>[] enums;
2701     private int index;
2702 
2703     public CompoundEnumeration(Enumeration<E>[] enums) {
2704         this.enums = enums;
2705     }
2706 
2707     private boolean next() {
2708         while (index < enums.length) {
2709             if (enums[index] != null && enums[index].hasMoreElements()) {
2710                 return true;
2711             }
2712             index++;
2713         }
2714         return false;
2715     }
2716 
2717     public boolean hasMoreElements() {
2718         return next();
2719     }
2720 
2721     public E nextElement() {
2722         if (!next()) {
2723             throw new NoSuchElementException();
2724         }
2725         return enums[index].nextElement();
2726     }
2727 }