1 /*
   2  * Copyright (c) 1994, 2018, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.  Oracle designates this
   8  * particular file as subject to the "Classpath" exception as provided
   9  * by Oracle in the LICENSE file that accompanied this code.
  10  *
  11  * This code is distributed in the hope that it will be useful, but WITHOUT
  12  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  13  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  14  * version 2 for more details (a copy is included in the LICENSE file that
  15  * accompanied this code).
  16  *
  17  * You should have received a copy of the GNU General Public License version
  18  * 2 along with this work; if not, write to the Free Software Foundation,
  19  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  20  *
  21  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  22  * or visit www.oracle.com if you need additional information or have any
  23  * questions.
  24  */
  25 package java.lang;
  26 
  27 import java.io.BufferedInputStream;
  28 import java.io.BufferedOutputStream;
  29 import java.io.Console;
  30 import java.io.FileDescriptor;
  31 import java.io.FileInputStream;
  32 import java.io.FileOutputStream;
  33 import java.io.IOException;
  34 import java.io.InputStream;
  35 import java.io.PrintStream;
  36 import java.io.UnsupportedEncodingException;
  37 import java.lang.annotation.Annotation;
  38 import java.lang.module.ModuleDescriptor;
  39 import java.lang.reflect.Constructor;
  40 import java.lang.reflect.Executable;
  41 import java.lang.reflect.Method;
  42 import java.lang.reflect.Modifier;
  43 import java.net.URI;
  44 import java.nio.charset.CharacterCodingException;
  45 import java.security.AccessControlContext;
  46 import java.security.ProtectionDomain;
  47 import java.security.AccessController;
  48 import java.security.PrivilegedAction;
  49 import java.nio.channels.Channel;
  50 import java.nio.channels.spi.SelectorProvider;
  51 import java.nio.charset.Charset;
  52 import java.util.Iterator;
  53 import java.util.List;
  54 import java.util.Map;
  55 import java.util.Objects;
  56 import java.util.Properties;
  57 import java.util.PropertyPermission;
  58 import java.util.ResourceBundle;
  59 import java.util.function.Supplier;
  60 import java.util.concurrent.ConcurrentHashMap;
  61 import java.util.stream.Stream;
  62 
  63 import jdk.internal.util.StaticProperty;
  64 import jdk.internal.module.ModuleBootstrap;
  65 import jdk.internal.module.ServicesCatalog;
  66 import jdk.internal.reflect.CallerSensitive;
  67 import jdk.internal.reflect.Reflection;
  68 import jdk.internal.HotSpotIntrinsicCandidate;
  69 import jdk.internal.misc.JavaLangAccess;
  70 import jdk.internal.misc.SharedSecrets;
  71 import jdk.internal.misc.VM;
  72 import jdk.internal.logger.LoggerFinderLoader;
  73 import jdk.internal.logger.LazyLoggers;
  74 import jdk.internal.logger.LocalizedLoggerWrapper;
  75 import sun.reflect.annotation.AnnotationType;
  76 import sun.nio.ch.Interruptible;
  77 import sun.security.util.SecurityConstants;
  78 
  79 /**
  80  * The {@code System} class contains several useful class fields
  81  * and methods. It cannot be instantiated.
  82  *
  83  * Among the facilities provided by the {@code System} class
  84  * are standard input, standard output, and error output streams;
  85  * access to externally defined properties and environment
  86  * variables; a means of loading files and libraries; and a utility
  87  * method for quickly copying a portion of an array.
  88  *
  89  * @since   1.0
  90  */
  91 public final class System {
  92     /* Register the natives via the static initializer.
  93      *
  94      * VM will invoke the initializeSystemClass method to complete
  95      * the initialization for this class separated from clinit.
  96      * Note that to use properties set by the VM, see the constraints
  97      * described in the initializeSystemClass method.
  98      */
  99     private static native void registerNatives();
 100     static {
 101         registerNatives();
 102     }
 103 
 104     /** Don't let anyone instantiate this class */
 105     private System() {
 106     }
 107 
 108     /**
 109      * The "standard" input stream. This stream is already
 110      * open and ready to supply input data. Typically this stream
 111      * corresponds to keyboard input or another input source specified by
 112      * the host environment or user.
 113      */
 114     public static final InputStream in = null;
 115 
 116     /**
 117      * The "standard" output stream. This stream is already
 118      * open and ready to accept output data. Typically this stream
 119      * corresponds to display output or another output destination
 120      * specified by the host environment or user.
 121      * <p>
 122      * For simple stand-alone Java applications, a typical way to write
 123      * a line of output data is:
 124      * <blockquote><pre>
 125      *     System.out.println(data)
 126      * </pre></blockquote>
 127      * <p>
 128      * See the {@code println} methods in class {@code PrintStream}.
 129      *
 130      * @see     java.io.PrintStream#println()
 131      * @see     java.io.PrintStream#println(boolean)
 132      * @see     java.io.PrintStream#println(char)
 133      * @see     java.io.PrintStream#println(char[])
 134      * @see     java.io.PrintStream#println(double)
 135      * @see     java.io.PrintStream#println(float)
 136      * @see     java.io.PrintStream#println(int)
 137      * @see     java.io.PrintStream#println(long)
 138      * @see     java.io.PrintStream#println(java.lang.Object)
 139      * @see     java.io.PrintStream#println(java.lang.String)
 140      */
 141     public static final PrintStream out = null;
 142 
 143     /**
 144      * The "standard" error output stream. This stream is already
 145      * open and ready to accept output data.
 146      * <p>
 147      * Typically this stream corresponds to display output or another
 148      * output destination specified by the host environment or user. By
 149      * convention, this output stream is used to display error messages
 150      * or other information that should come to the immediate attention
 151      * of a user even if the principal output stream, the value of the
 152      * variable {@code out}, has been redirected to a file or other
 153      * destination that is typically not continuously monitored.
 154      */
 155     public static final PrintStream err = null;
 156 
 157     /* The security manager for the system.
 158      */
 159     private static volatile SecurityManager security;
 160 
 161     /**
 162      * Reassigns the "standard" input stream.
 163      *
 164      * First, if there is a security manager, its {@code checkPermission}
 165      * method is called with a {@code RuntimePermission("setIO")} permission
 166      *  to see if it's ok to reassign the "standard" input stream.
 167      *
 168      * @param in the new standard input stream.
 169      *
 170      * @throws SecurityException
 171      *        if a security manager exists and its
 172      *        {@code checkPermission} method doesn't allow
 173      *        reassigning of the standard input stream.
 174      *
 175      * @see SecurityManager#checkPermission
 176      * @see java.lang.RuntimePermission
 177      *
 178      * @since   1.1
 179      */
 180     public static void setIn(InputStream in) {
 181         checkIO();
 182         setIn0(in);
 183     }
 184 
 185     /**
 186      * Reassigns the "standard" output stream.
 187      *
 188      * First, if there is a security manager, its {@code checkPermission}
 189      * method is called with a {@code RuntimePermission("setIO")} permission
 190      *  to see if it's ok to reassign the "standard" output stream.
 191      *
 192      * @param out the new standard output stream
 193      *
 194      * @throws SecurityException
 195      *        if a security manager exists and its
 196      *        {@code checkPermission} method doesn't allow
 197      *        reassigning of the standard output stream.
 198      *
 199      * @see SecurityManager#checkPermission
 200      * @see java.lang.RuntimePermission
 201      *
 202      * @since   1.1
 203      */
 204     public static void setOut(PrintStream out) {
 205         checkIO();
 206         setOut0(out);
 207     }
 208 
 209     /**
 210      * Reassigns the "standard" error output stream.
 211      *
 212      * First, if there is a security manager, its {@code checkPermission}
 213      * method is called with a {@code RuntimePermission("setIO")} permission
 214      *  to see if it's ok to reassign the "standard" error output stream.
 215      *
 216      * @param err the new standard error output stream.
 217      *
 218      * @throws SecurityException
 219      *        if a security manager exists and its
 220      *        {@code checkPermission} method doesn't allow
 221      *        reassigning of the standard error output stream.
 222      *
 223      * @see SecurityManager#checkPermission
 224      * @see java.lang.RuntimePermission
 225      *
 226      * @since   1.1
 227      */
 228     public static void setErr(PrintStream err) {
 229         checkIO();
 230         setErr0(err);
 231     }
 232 
 233     private static volatile Console cons;
 234     /**
 235      * Returns the unique {@link java.io.Console Console} object associated
 236      * with the current Java virtual machine, if any.
 237      *
 238      * @return  The system console, if any, otherwise {@code null}.
 239      *
 240      * @since   1.6
 241      */
 242      public static Console console() {
 243          Console c;
 244          if ((c = cons) == null) {
 245              synchronized (System.class) {
 246                  if ((c = cons) == null) {
 247                      cons = c = SharedSecrets.getJavaIOAccess().console();
 248                  }
 249              }
 250          }
 251          return c;
 252      }
 253 
 254     /**
 255      * Returns the channel inherited from the entity that created this
 256      * Java virtual machine.
 257      *
 258      * This method returns the channel obtained by invoking the
 259      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
 260      * inheritedChannel} method of the system-wide default
 261      * {@link java.nio.channels.spi.SelectorProvider} object.
 262      *
 263      * <p> In addition to the network-oriented channels described in
 264      * {@link java.nio.channels.spi.SelectorProvider#inheritedChannel
 265      * inheritedChannel}, this method may return other kinds of
 266      * channels in the future.
 267      *
 268      * @return  The inherited channel, if any, otherwise {@code null}.
 269      *
 270      * @throws  IOException
 271      *          If an I/O error occurs
 272      *
 273      * @throws  SecurityException
 274      *          If a security manager is present and it does not
 275      *          permit access to the channel.
 276      *
 277      * @since 1.5
 278      */
 279     public static Channel inheritedChannel() throws IOException {
 280         return SelectorProvider.provider().inheritedChannel();
 281     }
 282 
 283     private static void checkIO() {
 284         SecurityManager sm = getSecurityManager();
 285         if (sm != null) {
 286             sm.checkPermission(new RuntimePermission("setIO"));
 287         }
 288     }
 289 
 290     private static native void setIn0(InputStream in);
 291     private static native void setOut0(PrintStream out);
 292     private static native void setErr0(PrintStream err);
 293 
 294     /**
 295      * Sets the System security.
 296      *
 297      * If there is a security manager already installed, this method first
 298      * calls the security manager's {@code checkPermission} method
 299      * with a {@code RuntimePermission("setSecurityManager")}
 300      * permission to ensure it's ok to replace the existing
 301      * security manager.
 302      * This may result in throwing a {@code SecurityException}.
 303      *
 304      * <p> Otherwise, the argument is established as the current
 305      * security manager. If the argument is {@code null} and no
 306      * security manager has been established, then no action is taken and
 307      * the method simply returns.
 308      *
 309      * @param      s   the security manager.
 310      * @throws     SecurityException  if the security manager has already
 311      *             been set and its {@code checkPermission} method
 312      *             doesn't allow it to be replaced.
 313      * @see #getSecurityManager
 314      * @see SecurityManager#checkPermission
 315      * @see java.lang.RuntimePermission
 316      */
 317     public static void setSecurityManager(final SecurityManager s) {
 318         if (security == null) {
 319             // ensure image reader is initialized
 320             Object.class.getResource("java/lang/ANY");
 321         }
 322         if (s != null) {
 323             try {
 324                 s.checkPackageAccess("java.lang");
 325             } catch (Exception e) {
 326                 // no-op
 327             }
 328         }
 329         setSecurityManager0(s);
 330     }
 331 
 332     private static synchronized
 333     void setSecurityManager0(final SecurityManager s) {
 334         SecurityManager sm = getSecurityManager();
 335         if (sm != null) {
 336             // ask the currently installed security manager if we
 337             // can replace it.
 338             sm.checkPermission(new RuntimePermission
 339                                      ("setSecurityManager"));
 340         }
 341 
 342         if ((s != null) && (s.getClass().getClassLoader() != null)) {
 343             // New security manager class is not on bootstrap classpath.
 344             // Cause policy to get initialized before we install the new
 345             // security manager, in order to prevent infinite loops when
 346             // trying to initialize the policy (which usually involves
 347             // accessing some security and/or system properties, which in turn
 348             // calls the installed security manager's checkPermission method
 349             // which will loop infinitely if there is a non-system class
 350             // (in this case: the new security manager class) on the stack).
 351             AccessController.doPrivileged(new PrivilegedAction<>() {
 352                 public Object run() {
 353                     s.getClass().getProtectionDomain().implies
 354                         (SecurityConstants.ALL_PERMISSION);
 355                     return null;
 356                 }
 357             });
 358         }
 359 
 360         security = s;
 361     }
 362 
 363     /**
 364      * Gets the system security interface.
 365      *
 366      * @return  if a security manager has already been established for the
 367      *          current application, then that security manager is returned;
 368      *          otherwise, {@code null} is returned.
 369      * @see     #setSecurityManager
 370      */
 371     public static SecurityManager getSecurityManager() {
 372         return security;
 373     }
 374 
 375     /**
 376      * Returns the current time in milliseconds.  Note that
 377      * while the unit of time of the return value is a millisecond,
 378      * the granularity of the value depends on the underlying
 379      * operating system and may be larger.  For example, many
 380      * operating systems measure time in units of tens of
 381      * milliseconds.
 382      *
 383      * <p> See the description of the class {@code Date} for
 384      * a discussion of slight discrepancies that may arise between
 385      * "computer time" and coordinated universal time (UTC).
 386      *
 387      * @return  the difference, measured in milliseconds, between
 388      *          the current time and midnight, January 1, 1970 UTC.
 389      * @see     java.util.Date
 390      */
 391     @HotSpotIntrinsicCandidate
 392     public static native long currentTimeMillis();
 393 
 394     /**
 395      * Returns the current value of the running Java Virtual Machine's
 396      * high-resolution time source, in nanoseconds.
 397      *
 398      * This method can only be used to measure elapsed time and is
 399      * not related to any other notion of system or wall-clock time.
 400      * The value returned represents nanoseconds since some fixed but
 401      * arbitrary <i>origin</i> time (perhaps in the future, so values
 402      * may be negative).  The same origin is used by all invocations of
 403      * this method in an instance of a Java virtual machine; other
 404      * virtual machine instances are likely to use a different origin.
 405      *
 406      * <p>This method provides nanosecond precision, but not necessarily
 407      * nanosecond resolution (that is, how frequently the value changes)
 408      * - no guarantees are made except that the resolution is at least as
 409      * good as that of {@link #currentTimeMillis()}.
 410      *
 411      * <p>Differences in successive calls that span greater than
 412      * approximately 292 years (2<sup>63</sup> nanoseconds) will not
 413      * correctly compute elapsed time due to numerical overflow.
 414      *
 415      * <p>The values returned by this method become meaningful only when
 416      * the difference between two such values, obtained within the same
 417      * instance of a Java virtual machine, is computed.
 418      *
 419      * <p>For example, to measure how long some code takes to execute:
 420      * <pre> {@code
 421      * long startTime = System.nanoTime();
 422      * // ... the code being measured ...
 423      * long elapsedNanos = System.nanoTime() - startTime;}</pre>
 424      *
 425      * <p>To compare elapsed time against a timeout, use <pre> {@code
 426      * if (System.nanoTime() - startTime >= timeoutNanos) ...}</pre>
 427      * instead of <pre> {@code
 428      * if (System.nanoTime() >= startTime + timeoutNanos) ...}</pre>
 429      * because of the possibility of numerical overflow.
 430      *
 431      * @return the current value of the running Java Virtual Machine's
 432      *         high-resolution time source, in nanoseconds
 433      * @since 1.5
 434      */
 435     @HotSpotIntrinsicCandidate
 436     public static native long nanoTime();
 437 
 438     /**
 439      * Copies an array from the specified source array, beginning at the
 440      * specified position, to the specified position of the destination array.
 441      * A subsequence of array components are copied from the source
 442      * array referenced by {@code src} to the destination array
 443      * referenced by {@code dest}. The number of components copied is
 444      * equal to the {@code length} argument. The components at
 445      * positions {@code srcPos} through
 446      * {@code srcPos+length-1} in the source array are copied into
 447      * positions {@code destPos} through
 448      * {@code destPos+length-1}, respectively, of the destination
 449      * array.
 450      * <p>
 451      * If the {@code src} and {@code dest} arguments refer to the
 452      * same array object, then the copying is performed as if the
 453      * components at positions {@code srcPos} through
 454      * {@code srcPos+length-1} were first copied to a temporary
 455      * array with {@code length} components and then the contents of
 456      * the temporary array were copied into positions
 457      * {@code destPos} through {@code destPos+length-1} of the
 458      * destination array.
 459      * <p>
 460      * If {@code dest} is {@code null}, then a
 461      * {@code NullPointerException} is thrown.
 462      * <p>
 463      * If {@code src} is {@code null}, then a
 464      * {@code NullPointerException} is thrown and the destination
 465      * array is not modified.
 466      * <p>
 467      * Otherwise, if any of the following is true, an
 468      * {@code ArrayStoreException} is thrown and the destination is
 469      * not modified:
 470      * <ul>
 471      * <li>The {@code src} argument refers to an object that is not an
 472      *     array.
 473      * <li>The {@code dest} argument refers to an object that is not an
 474      *     array.
 475      * <li>The {@code src} argument and {@code dest} argument refer
 476      *     to arrays whose component types are different primitive types.
 477      * <li>The {@code src} argument refers to an array with a primitive
 478      *    component type and the {@code dest} argument refers to an array
 479      *     with a reference component type.
 480      * <li>The {@code src} argument refers to an array with a reference
 481      *    component type and the {@code dest} argument refers to an array
 482      *     with a primitive component type.
 483      * </ul>
 484      * <p>
 485      * Otherwise, if any of the following is true, an
 486      * {@code IndexOutOfBoundsException} is
 487      * thrown and the destination is not modified:
 488      * <ul>
 489      * <li>The {@code srcPos} argument is negative.
 490      * <li>The {@code destPos} argument is negative.
 491      * <li>The {@code length} argument is negative.
 492      * <li>{@code srcPos+length} is greater than
 493      *     {@code src.length}, the length of the source array.
 494      * <li>{@code destPos+length} is greater than
 495      *     {@code dest.length}, the length of the destination array.
 496      * </ul>
 497      * <p>
 498      * Otherwise, if any actual component of the source array from
 499      * position {@code srcPos} through
 500      * {@code srcPos+length-1} cannot be converted to the component
 501      * type of the destination array by assignment conversion, an
 502      * {@code ArrayStoreException} is thrown. In this case, let
 503      * <b><i>k</i></b> be the smallest nonnegative integer less than
 504      * length such that {@code src[srcPos+}<i>k</i>{@code ]}
 505      * cannot be converted to the component type of the destination
 506      * array; when the exception is thrown, source array components from
 507      * positions {@code srcPos} through
 508      * {@code srcPos+}<i>k</i>{@code -1}
 509      * will already have been copied to destination array positions
 510      * {@code destPos} through
 511      * {@code destPos+}<i>k</I>{@code -1} and no other
 512      * positions of the destination array will have been modified.
 513      * (Because of the restrictions already itemized, this
 514      * paragraph effectively applies only to the situation where both
 515      * arrays have component types that are reference types.)
 516      *
 517      * @param      src      the source array.
 518      * @param      srcPos   starting position in the source array.
 519      * @param      dest     the destination array.
 520      * @param      destPos  starting position in the destination data.
 521      * @param      length   the number of array elements to be copied.
 522      * @throws     IndexOutOfBoundsException  if copying would cause
 523      *             access of data outside array bounds.
 524      * @throws     ArrayStoreException  if an element in the {@code src}
 525      *             array could not be stored into the {@code dest} array
 526      *             because of a type mismatch.
 527      * @throws     NullPointerException if either {@code src} or
 528      *             {@code dest} is {@code null}.
 529      */
 530     @HotSpotIntrinsicCandidate
 531     public static native void arraycopy(Object src,  int  srcPos,
 532                                         Object dest, int destPos,
 533                                         int length);
 534 
 535     /**
 536      * Returns the same hash code for the given object as
 537      * would be returned by the default method hashCode(),
 538      * whether or not the given object's class overrides
 539      * hashCode().
 540      * The hash code for the null reference is zero.
 541      *
 542      * @param x object for which the hashCode is to be calculated
 543      * @return  the hashCode
 544      * @since   1.1
 545      * @see Object#hashCode
 546      * @see java.util.Objects#hashCode(Object)
 547      */
 548     @HotSpotIntrinsicCandidate
 549     public static native int identityHashCode(Object x);
 550 
 551     /**
 552      * System properties. The following properties are guaranteed to be defined:
 553      * <dl>
 554      * <dt>java.version         <dd>Java version number
 555      * <dt>java.version.date    <dd>Java version date
 556      * <dt>java.vendor          <dd>Java vendor specific string
 557      * <dt>java.vendor.url      <dd>Java vendor URL
 558      * <dt>java.vendor.version  <dd>Java vendor version
 559      * <dt>java.home            <dd>Java installation directory
 560      * <dt>java.class.version   <dd>Java class version number
 561      * <dt>java.class.path      <dd>Java classpath
 562      * <dt>os.name              <dd>Operating System Name
 563      * <dt>os.arch              <dd>Operating System Architecture
 564      * <dt>os.version           <dd>Operating System Version
 565      * <dt>file.separator       <dd>File separator ("/" on Unix)
 566      * <dt>path.separator       <dd>Path separator (":" on Unix)
 567      * <dt>line.separator       <dd>Line separator ("\n" on Unix)
 568      * <dt>user.name            <dd>User account name
 569      * <dt>user.home            <dd>User home directory
 570      * <dt>user.dir             <dd>User's current working directory
 571      * </dl>
 572      */
 573 
 574     private static Properties props;
 575     private static native Properties initProperties(Properties props);
 576 
 577     /**
 578      * Determines the current system properties.
 579      *
 580      * First, if there is a security manager, its
 581      * {@code checkPropertiesAccess} method is called with no
 582      * arguments. This may result in a security exception.
 583      * <p>
 584      * The current set of system properties for use by the
 585      * {@link #getProperty(String)} method is returned as a
 586      * {@code Properties} object. If there is no current set of
 587      * system properties, a set of system properties is first created and
 588      * initialized. This set of system properties always includes values
 589      * for the following keys:
 590      * <table class="striped" style="text-align:left">
 591      * <caption style="display:none">Shows property keys and associated values</caption>
 592      * <thead>
 593      * <tr><th scope="col">Key</th>
 594      *     <th scope="col">Description of Associated Value</th></tr>
 595      * </thead>
 596      * <tbody>
 597      * <tr><th scope="row">{@code java.version}</th>
 598      *     <td>Java Runtime Environment version, which may be interpreted
 599      *     as a {@link Runtime.Version}</td></tr>
 600      * <tr><th scope="row">{@code java.version.date}</th>
 601      *     <td>Java Runtime Environment version date, in ISO-8601 YYYY-MM-DD
 602      *     format, which may be interpreted as a {@link
 603      *     java.time.LocalDate}</td></tr>
 604      * <tr><th scope="row">{@code java.vendor}</th>
 605      *     <td>Java Runtime Environment vendor</td></tr>
 606      * <tr><th scope="row">{@code java.vendor.url}</th>
 607      *     <td>Java vendor URL</td></tr>
 608      * <tr><th scope="row">{@code java.vendor.version}</th>
 609      *     <td>Java vendor version</td></tr>
 610      * <tr><th scope="row">{@code java.home}</th>
 611      *     <td>Java installation directory</td></tr>
 612      * <tr><th scope="row">{@code java.vm.specification.version}</th>
 613      *     <td>Java Virtual Machine specification version, whose value is the
 614      *     {@linkplain Runtime.Version#feature feature} element of the
 615      *     {@linkplain Runtime#version() runtime version}</td></tr>
 616      * <tr><th scope="row">{@code java.vm.specification.vendor}</th>
 617      *     <td>Java Virtual Machine specification vendor</td></tr>
 618      * <tr><th scope="row">{@code java.vm.specification.name}</th>
 619      *     <td>Java Virtual Machine specification name</td></tr>
 620      * <tr><th scope="row">{@code java.vm.version}</th>
 621      *     <td>Java Virtual Machine implementation version which may be
 622      *     interpreted as a {@link Runtime.Version}</td></tr>
 623      * <tr><th scope="row">{@code java.vm.vendor}</th>
 624      *     <td>Java Virtual Machine implementation vendor</td></tr>
 625      * <tr><th scope="row">{@code java.vm.name}</th>
 626      *     <td>Java Virtual Machine implementation name</td></tr>
 627      * <tr><th scope="row">{@code java.specification.version}</th>
 628      *     <td>Java Runtime Environment specification version, whose value is
 629      *     the {@linkplain Runtime.Version#feature feature} element of the
 630      *     {@linkplain Runtime#version() runtime version}</td></tr>
 631      * <tr><th scope="row">{@code java.specification.vendor}</th>
 632      *     <td>Java Runtime Environment specification  vendor</td></tr>
 633      * <tr><th scope="row">{@code java.specification.name}</th>
 634      *     <td>Java Runtime Environment specification  name</td></tr>
 635      * <tr><th scope="row">{@code java.class.version}</th>
 636      *     <td>Java class format version number</td></tr>
 637      * <tr><th scope="row">{@code java.class.path}</th>
 638      *     <td>Java class path  (refer to
 639      *        {@link ClassLoader#getSystemClassLoader()} for details)</td></tr>
 640      * <tr><th scope="row">{@code java.library.path}</th>
 641      *     <td>List of paths to search when loading libraries</td></tr>
 642      * <tr><th scope="row">{@code java.io.tmpdir}</th>
 643      *     <td>Default temp file path</td></tr>
 644      * <tr><th scope="row">{@code java.compiler}</th>
 645      *     <td>Name of JIT compiler to use</td></tr>
 646      * <tr><th scope="row">{@code os.name}</th>
 647      *     <td>Operating system name</td></tr>
 648      * <tr><th scope="row">{@code os.arch}</th>
 649      *     <td>Operating system architecture</td></tr>
 650      * <tr><th scope="row">{@code os.version}</th>
 651      *     <td>Operating system version</td></tr>
 652      * <tr><th scope="row">{@code file.separator}</th>
 653      *     <td>File separator ("/" on UNIX)</td></tr>
 654      * <tr><th scope="row">{@code path.separator}</th>
 655      *     <td>Path separator (":" on UNIX)</td></tr>
 656      * <tr><th scope="row">{@code line.separator}</th>
 657      *     <td>Line separator ("\n" on UNIX)</td></tr>
 658      * <tr><th scope="row">{@code user.name}</th>
 659      *     <td>User's account name</td></tr>
 660      * <tr><th scope="row">{@code user.home}</th>
 661      *     <td>User's home directory</td></tr>
 662      * <tr><th scope="row">{@code user.dir}</th>
 663      *     <td>User's current working directory</td></tr>
 664      * </tbody>
 665      * </table>
 666      * <p>
 667      * Multiple paths in a system property value are separated by the path
 668      * separator character of the platform.
 669      * <p>
 670      * Note that even if the security manager does not permit the
 671      * {@code getProperties} operation, it may choose to permit the
 672      * {@link #getProperty(String)} operation.
 673      *
 674      * @apiNote
 675      * <strong>Changing a standard system property may have unpredictable results
 676      * unless otherwise specified.</strong>
 677      * Property values may be cached during initialization or on first use.
 678      * Setting a standard property after initialization using {@link #getProperties()},
 679      * {@link #setProperties(Properties)}, {@link #setProperty(String, String)}, or
 680      * {@link #clearProperty(String)} may not have the desired effect.
 681      *
 682      * @implNote
 683      * In addition to the standard system properties, the system
 684      * properties may include the following keys:
 685      * <table class="striped">
 686      * <caption style="display:none">Shows property keys and associated values</caption>
 687      * <thead>
 688      * <tr><th scope="col">Key</th>
 689      *     <th scope="col">Description of Associated Value</th></tr>
 690      * </thead>
 691      * <tbody>
 692      * <tr><th scope="row">{@code jdk.module.path}</th>
 693      *     <td>The application module path</td></tr>
 694      * <tr><th scope="row">{@code jdk.module.upgrade.path}</th>
 695      *     <td>The upgrade module path</td></tr>
 696      * <tr><th scope="row">{@code jdk.module.main}</th>
 697      *     <td>The module name of the initial/main module</td></tr>
 698      * <tr><th scope="row">{@code jdk.module.main.class}</th>
 699      *     <td>The main class name of the initial module</td></tr>
 700      * </tbody>
 701      * </table>
 702      *
 703      * @return     the system properties
 704      * @throws     SecurityException  if a security manager exists and its
 705      *             {@code checkPropertiesAccess} method doesn't allow access
 706      *             to the system properties.
 707      * @see        #setProperties
 708      * @see        java.lang.SecurityException
 709      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 710      * @see        java.util.Properties
 711      */
 712     public static Properties getProperties() {
 713         SecurityManager sm = getSecurityManager();
 714         if (sm != null) {
 715             sm.checkPropertiesAccess();
 716         }
 717 
 718         return props;
 719     }
 720 
 721     /**
 722      * Returns the system-dependent line separator string.  It always
 723      * returns the same value - the initial value of the {@linkplain
 724      * #getProperty(String) system property} {@code line.separator}.
 725      *
 726      * <p>On UNIX systems, it returns {@code "\n"}; on Microsoft
 727      * Windows systems it returns {@code "\r\n"}.
 728      *
 729      * @return the system-dependent line separator string
 730      * @since 1.7
 731      */
 732     public static String lineSeparator() {
 733         return lineSeparator;
 734     }
 735 
 736     private static String lineSeparator;
 737 
 738     /**
 739      * Sets the system properties to the {@code Properties} argument.
 740      *
 741      * First, if there is a security manager, its
 742      * {@code checkPropertiesAccess} method is called with no
 743      * arguments. This may result in a security exception.
 744      * <p>
 745      * The argument becomes the current set of system properties for use
 746      * by the {@link #getProperty(String)} method. If the argument is
 747      * {@code null}, then the current set of system properties is
 748      * forgotten.
 749      *
 750      * @apiNote
 751      * <strong>Changing a standard system property may have unpredictable results
 752      * unless otherwise specified</strong>.
 753      * See {@linkplain #getProperties getProperties} for details.
 754      *
 755      * @param      props   the new system properties.
 756      * @throws     SecurityException  if a security manager exists and its
 757      *             {@code checkPropertiesAccess} method doesn't allow access
 758      *             to the system properties.
 759      * @see        #getProperties
 760      * @see        java.util.Properties
 761      * @see        java.lang.SecurityException
 762      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 763      */
 764     public static void setProperties(Properties props) {
 765         SecurityManager sm = getSecurityManager();
 766         if (sm != null) {
 767             sm.checkPropertiesAccess();
 768         }
 769         if (props == null) {
 770             props = new Properties();
 771             initProperties(props);
 772         }
 773         System.props = props;
 774     }
 775 
 776     /**
 777      * Gets the system property indicated by the specified key.
 778      *
 779      * First, if there is a security manager, its
 780      * {@code checkPropertyAccess} method is called with the key as
 781      * its argument. This may result in a SecurityException.
 782      * <p>
 783      * If there is no current set of system properties, a set of system
 784      * properties is first created and initialized in the same manner as
 785      * for the {@code getProperties} method.
 786      *
 787      * @apiNote
 788      * <strong>Changing a standard system property may have unpredictable results
 789      * unless otherwise specified</strong>.
 790      * See {@linkplain #getProperties getProperties} for details.
 791      *
 792      * @param      key   the name of the system property.
 793      * @return     the string value of the system property,
 794      *             or {@code null} if there is no property with that key.
 795      *
 796      * @throws     SecurityException  if a security manager exists and its
 797      *             {@code checkPropertyAccess} method doesn't allow
 798      *             access to the specified system property.
 799      * @throws     NullPointerException if {@code key} is {@code null}.
 800      * @throws     IllegalArgumentException if {@code key} is empty.
 801      * @see        #setProperty
 802      * @see        java.lang.SecurityException
 803      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
 804      * @see        java.lang.System#getProperties()
 805      */
 806     public static String getProperty(String key) {
 807         checkKey(key);
 808         SecurityManager sm = getSecurityManager();
 809         if (sm != null) {
 810             sm.checkPropertyAccess(key);
 811         }
 812 
 813         return props.getProperty(key);
 814     }
 815 
 816     /**
 817      * Gets the system property indicated by the specified key.
 818      *
 819      * First, if there is a security manager, its
 820      * {@code checkPropertyAccess} method is called with the
 821      * {@code key} as its argument.
 822      * <p>
 823      * If there is no current set of system properties, a set of system
 824      * properties is first created and initialized in the same manner as
 825      * for the {@code getProperties} method.
 826      *
 827      * @param      key   the name of the system property.
 828      * @param      def   a default value.
 829      * @return     the string value of the system property,
 830      *             or the default value if there is no property with that key.
 831      *
 832      * @throws     SecurityException  if a security manager exists and its
 833      *             {@code checkPropertyAccess} method doesn't allow
 834      *             access to the specified system property.
 835      * @throws     NullPointerException if {@code key} is {@code null}.
 836      * @throws     IllegalArgumentException if {@code key} is empty.
 837      * @see        #setProperty
 838      * @see        java.lang.SecurityManager#checkPropertyAccess(java.lang.String)
 839      * @see        java.lang.System#getProperties()
 840      */
 841     public static String getProperty(String key, String def) {
 842         checkKey(key);
 843         SecurityManager sm = getSecurityManager();
 844         if (sm != null) {
 845             sm.checkPropertyAccess(key);
 846         }
 847 
 848         return props.getProperty(key, def);
 849     }
 850 
 851     /**
 852      * Sets the system property indicated by the specified key.
 853      *
 854      * First, if a security manager exists, its
 855      * {@code SecurityManager.checkPermission} method
 856      * is called with a {@code PropertyPermission(key, "write")}
 857      * permission. This may result in a SecurityException being thrown.
 858      * If no exception is thrown, the specified property is set to the given
 859      * value.
 860      *
 861      * @apiNote
 862      * <strong>Changing a standard system property may have unpredictable results
 863      * unless otherwise specified</strong>.
 864      * See {@linkplain #getProperties getProperties} for details.
 865      *
 866      * @param      key   the name of the system property.
 867      * @param      value the value of the system property.
 868      * @return     the previous value of the system property,
 869      *             or {@code null} if it did not have one.
 870      *
 871      * @throws     SecurityException  if a security manager exists and its
 872      *             {@code checkPermission} method doesn't allow
 873      *             setting of the specified property.
 874      * @throws     NullPointerException if {@code key} or
 875      *             {@code value} is {@code null}.
 876      * @throws     IllegalArgumentException if {@code key} is empty.
 877      * @see        #getProperty
 878      * @see        java.lang.System#getProperty(java.lang.String)
 879      * @see        java.lang.System#getProperty(java.lang.String, java.lang.String)
 880      * @see        java.util.PropertyPermission
 881      * @see        SecurityManager#checkPermission
 882      * @since      1.2
 883      */
 884     public static String setProperty(String key, String value) {
 885         checkKey(key);
 886         SecurityManager sm = getSecurityManager();
 887         if (sm != null) {
 888             sm.checkPermission(new PropertyPermission(key,
 889                 SecurityConstants.PROPERTY_WRITE_ACTION));
 890         }
 891 
 892         return (String) props.setProperty(key, value);
 893     }
 894 
 895     /**
 896      * Removes the system property indicated by the specified key.
 897      *
 898      * First, if a security manager exists, its
 899      * {@code SecurityManager.checkPermission} method
 900      * is called with a {@code PropertyPermission(key, "write")}
 901      * permission. This may result in a SecurityException being thrown.
 902      * If no exception is thrown, the specified property is removed.
 903      *
 904      * @apiNote
 905      * <strong>Changing a standard system property may have unpredictable results
 906      * unless otherwise specified</strong>.
 907      * See {@linkplain #getProperties getProperties} method for details.
 908      *
 909      * @param      key   the name of the system property to be removed.
 910      * @return     the previous string value of the system property,
 911      *             or {@code null} if there was no property with that key.
 912      *
 913      * @throws     SecurityException  if a security manager exists and its
 914      *             {@code checkPropertyAccess} method doesn't allow
 915      *              access to the specified system property.
 916      * @throws     NullPointerException if {@code key} is {@code null}.
 917      * @throws     IllegalArgumentException if {@code key} is empty.
 918      * @see        #getProperty
 919      * @see        #setProperty
 920      * @see        java.util.Properties
 921      * @see        java.lang.SecurityException
 922      * @see        java.lang.SecurityManager#checkPropertiesAccess()
 923      * @since 1.5
 924      */
 925     public static String clearProperty(String key) {
 926         checkKey(key);
 927         SecurityManager sm = getSecurityManager();
 928         if (sm != null) {
 929             sm.checkPermission(new PropertyPermission(key, "write"));
 930         }
 931 
 932         return (String) props.remove(key);
 933     }
 934 
 935     private static void checkKey(String key) {
 936         if (key == null) {
 937             throw new NullPointerException("key can't be null");
 938         }
 939         if (key.equals("")) {
 940             throw new IllegalArgumentException("key can't be empty");
 941         }
 942     }
 943 
 944     /**
 945      * Gets the value of the specified environment variable. An
 946      * environment variable is a system-dependent external named
 947      * value.
 948      *
 949      * <p>If a security manager exists, its
 950      * {@link SecurityManager#checkPermission checkPermission}
 951      * method is called with a
 952      * {@code {@link RuntimePermission}("getenv."+name)}
 953      * permission.  This may result in a {@link SecurityException}
 954      * being thrown.  If no exception is thrown the value of the
 955      * variable {@code name} is returned.
 956      *
 957      * <p><a id="EnvironmentVSSystemProperties"><i>System
 958      * properties</i> and <i>environment variables</i></a> are both
 959      * conceptually mappings between names and values.  Both
 960      * mechanisms can be used to pass user-defined information to a
 961      * Java process.  Environment variables have a more global effect,
 962      * because they are visible to all descendants of the process
 963      * which defines them, not just the immediate Java subprocess.
 964      * They can have subtly different semantics, such as case
 965      * insensitivity, on different operating systems.  For these
 966      * reasons, environment variables are more likely to have
 967      * unintended side effects.  It is best to use system properties
 968      * where possible.  Environment variables should be used when a
 969      * global effect is desired, or when an external system interface
 970      * requires an environment variable (such as {@code PATH}).
 971      *
 972      * <p>On UNIX systems the alphabetic case of {@code name} is
 973      * typically significant, while on Microsoft Windows systems it is
 974      * typically not.  For example, the expression
 975      * {@code System.getenv("FOO").equals(System.getenv("foo"))}
 976      * is likely to be true on Microsoft Windows.
 977      *
 978      * @param  name the name of the environment variable
 979      * @return the string value of the variable, or {@code null}
 980      *         if the variable is not defined in the system environment
 981      * @throws NullPointerException if {@code name} is {@code null}
 982      * @throws SecurityException
 983      *         if a security manager exists and its
 984      *         {@link SecurityManager#checkPermission checkPermission}
 985      *         method doesn't allow access to the environment variable
 986      *         {@code name}
 987      * @see    #getenv()
 988      * @see    ProcessBuilder#environment()
 989      */
 990     public static String getenv(String name) {
 991         SecurityManager sm = getSecurityManager();
 992         if (sm != null) {
 993             sm.checkPermission(new RuntimePermission("getenv."+name));
 994         }
 995 
 996         return ProcessEnvironment.getenv(name);
 997     }
 998 
 999 
1000     /**
1001      * Returns an unmodifiable string map view of the current system environment.
1002      * The environment is a system-dependent mapping from names to
1003      * values which is passed from parent to child processes.
1004      *
1005      * <p>If the system does not support environment variables, an
1006      * empty map is returned.
1007      *
1008      * <p>The returned map will never contain null keys or values.
1009      * Attempting to query the presence of a null key or value will
1010      * throw a {@link NullPointerException}.  Attempting to query
1011      * the presence of a key or value which is not of type
1012      * {@link String} will throw a {@link ClassCastException}.
1013      *
1014      * <p>The returned map and its collection views may not obey the
1015      * general contract of the {@link Object#equals} and
1016      * {@link Object#hashCode} methods.
1017      *
1018      * <p>The returned map is typically case-sensitive on all platforms.
1019      *
1020      * <p>If a security manager exists, its
1021      * {@link SecurityManager#checkPermission checkPermission}
1022      * method is called with a
1023      * {@code {@link RuntimePermission}("getenv.*")} permission.
1024      * This may result in a {@link SecurityException} being thrown.
1025      *
1026      * <p>When passing information to a Java subprocess,
1027      * <a href=#EnvironmentVSSystemProperties>system properties</a>
1028      * are generally preferred over environment variables.
1029      *
1030      * @return the environment as a map of variable names to values
1031      * @throws SecurityException
1032      *         if a security manager exists and its
1033      *         {@link SecurityManager#checkPermission checkPermission}
1034      *         method doesn't allow access to the process environment
1035      * @see    #getenv(String)
1036      * @see    ProcessBuilder#environment()
1037      * @since  1.5
1038      */
1039     public static java.util.Map<String,String> getenv() {
1040         SecurityManager sm = getSecurityManager();
1041         if (sm != null) {
1042             sm.checkPermission(new RuntimePermission("getenv.*"));
1043         }
1044 
1045         return ProcessEnvironment.getenv();
1046     }
1047 
1048     /**
1049      * {@code System.Logger} instances log messages that will be
1050      * routed to the underlying logging framework the {@link System.LoggerFinder
1051      * LoggerFinder} uses.
1052      *
1053      * {@code System.Logger} instances are typically obtained from
1054      * the {@link java.lang.System System} class, by calling
1055      * {@link java.lang.System#getLogger(java.lang.String) System.getLogger(loggerName)}
1056      * or {@link java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)
1057      * System.getLogger(loggerName, bundle)}.
1058      *
1059      * @see java.lang.System#getLogger(java.lang.String)
1060      * @see java.lang.System#getLogger(java.lang.String, java.util.ResourceBundle)
1061      * @see java.lang.System.LoggerFinder
1062      *
1063      * @since 9
1064      */
1065     public interface Logger {
1066 
1067         /**
1068          * System {@linkplain Logger loggers} levels.
1069          *
1070          * A level has a {@linkplain #getName() name} and {@linkplain
1071          * #getSeverity() severity}.
1072          * Level values are {@link #ALL}, {@link #TRACE}, {@link #DEBUG},
1073          * {@link #INFO}, {@link #WARNING}, {@link #ERROR}, {@link #OFF},
1074          * by order of increasing severity.
1075          * <br>
1076          * {@link #ALL} and {@link #OFF}
1077          * are simple markers with severities mapped respectively to
1078          * {@link java.lang.Integer#MIN_VALUE Integer.MIN_VALUE} and
1079          * {@link java.lang.Integer#MAX_VALUE Integer.MAX_VALUE}.
1080          * <p>
1081          * <b>Severity values and Mapping to {@code java.util.logging.Level}.</b>
1082          * <p>
1083          * {@linkplain System.Logger.Level System logger levels} are mapped to
1084          * {@linkplain java.util.logging.Level  java.util.logging levels}
1085          * of corresponding severity.
1086          * <br>The mapping is as follows:
1087          * <br><br>
1088          * <table class="striped">
1089          * <caption>System.Logger Severity Level Mapping</caption>
1090          * <thead>
1091          * <tr><th scope="col">System.Logger Levels</th>
1092          *     <th scope="col">java.util.logging Levels</th>
1093          * </thead>
1094          * <tbody>
1095          * <tr><th scope="row">{@link Logger.Level#ALL ALL}</th>
1096          *     <td>{@link java.util.logging.Level#ALL ALL}</td>
1097          * <tr><th scope="row">{@link Logger.Level#TRACE TRACE}</th>
1098          *     <td>{@link java.util.logging.Level#FINER FINER}</td>
1099          * <tr><th scope="row">{@link Logger.Level#DEBUG DEBUG}</th>
1100          *     <td>{@link java.util.logging.Level#FINE FINE}</td>
1101          * <tr><th scope="row">{@link Logger.Level#INFO INFO}</th>
1102          *     <td>{@link java.util.logging.Level#INFO INFO}</td>
1103          * <tr><th scope="row">{@link Logger.Level#WARNING WARNING}</th>
1104          *     <td>{@link java.util.logging.Level#WARNING WARNING}</td>
1105          * <tr><th scope="row">{@link Logger.Level#ERROR ERROR}</th>
1106          *     <td>{@link java.util.logging.Level#SEVERE SEVERE}</td>
1107          * <tr><th scope="row">{@link Logger.Level#OFF OFF}</th>
1108          *     <td>{@link java.util.logging.Level#OFF OFF}</td>
1109          * </tbody>
1110          * </table>
1111          *
1112          * @since 9
1113          *
1114          * @see java.lang.System.LoggerFinder
1115          * @see java.lang.System.Logger
1116          */
1117         public enum Level {
1118 
1119             // for convenience, we're reusing java.util.logging.Level int values
1120             // the mapping logic in sun.util.logging.PlatformLogger depends
1121             // on this.
1122             /**
1123              * A marker to indicate that all levels are enabled.
1124              * This level {@linkplain #getSeverity() severity} is
1125              * {@link Integer#MIN_VALUE}.
1126              */
1127             ALL(Integer.MIN_VALUE),  // typically mapped to/from j.u.l.Level.ALL
1128             /**
1129              * {@code TRACE} level: usually used to log diagnostic information.
1130              * This level {@linkplain #getSeverity() severity} is
1131              * {@code 400}.
1132              */
1133             TRACE(400),   // typically mapped to/from j.u.l.Level.FINER
1134             /**
1135              * {@code DEBUG} level: usually used to log debug information traces.
1136              * This level {@linkplain #getSeverity() severity} is
1137              * {@code 500}.
1138              */
1139             DEBUG(500),   // typically mapped to/from j.u.l.Level.FINEST/FINE/CONFIG
1140             /**
1141              * {@code INFO} level: usually used to log information messages.
1142              * This level {@linkplain #getSeverity() severity} is
1143              * {@code 800}.
1144              */
1145             INFO(800),    // typically mapped to/from j.u.l.Level.INFO
1146             /**
1147              * {@code WARNING} level: usually used to log warning messages.
1148              * This level {@linkplain #getSeverity() severity} is
1149              * {@code 900}.
1150              */
1151             WARNING(900), // typically mapped to/from j.u.l.Level.WARNING
1152             /**
1153              * {@code ERROR} level: usually used to log error messages.
1154              * This level {@linkplain #getSeverity() severity} is
1155              * {@code 1000}.
1156              */
1157             ERROR(1000),  // typically mapped to/from j.u.l.Level.SEVERE
1158             /**
1159              * A marker to indicate that all levels are disabled.
1160              * This level {@linkplain #getSeverity() severity} is
1161              * {@link Integer#MAX_VALUE}.
1162              */
1163             OFF(Integer.MAX_VALUE);  // typically mapped to/from j.u.l.Level.OFF
1164 
1165             private final int severity;
1166 
1167             private Level(int severity) {
1168                 this.severity = severity;
1169             }
1170 
1171             /**
1172              * Returns the name of this level.
1173              * @return this level {@linkplain #name()}.
1174              */
1175             public final String getName() {
1176                 return name();
1177             }
1178 
1179             /**
1180              * Returns the severity of this level.
1181              * A higher severity means a more severe condition.
1182              * @return this level severity.
1183              */
1184             public final int getSeverity() {
1185                 return severity;
1186             }
1187         }
1188 
1189         /**
1190          * Returns the name of this logger.
1191          *
1192          * @return the logger name.
1193          */
1194         public String getName();
1195 
1196         /**
1197          * Checks if a message of the given level would be logged by
1198          * this logger.
1199          *
1200          * @param level the log message level.
1201          * @return {@code true} if the given log message level is currently
1202          *         being logged.
1203          *
1204          * @throws NullPointerException if {@code level} is {@code null}.
1205          */
1206         public boolean isLoggable(Level level);
1207 
1208         /**
1209          * Logs a message.
1210          *
1211          * @implSpec The default implementation for this method calls
1212          * {@code this.log(level, (ResourceBundle)null, msg, (Object[])null);}
1213          *
1214          * @param level the log message level.
1215          * @param msg the string message (or a key in the message catalog, if
1216          * this logger is a {@link
1217          * LoggerFinder#getLocalizedLogger(java.lang.String,
1218          * java.util.ResourceBundle, java.lang.Module) localized logger});
1219          * can be {@code null}.
1220          *
1221          * @throws NullPointerException if {@code level} is {@code null}.
1222          */
1223         public default void log(Level level, String msg) {
1224             log(level, (ResourceBundle) null, msg, (Object[]) null);
1225         }
1226 
1227         /**
1228          * Logs a lazily supplied message.
1229          *
1230          * If the logger is currently enabled for the given log message level
1231          * then a message is logged that is the result produced by the
1232          * given supplier function.  Otherwise, the supplier is not operated on.
1233          *
1234          * @implSpec When logging is enabled for the given level, the default
1235          * implementation for this method calls
1236          * {@code this.log(level, (ResourceBundle)null, msgSupplier.get(), (Object[])null);}
1237          *
1238          * @param level the log message level.
1239          * @param msgSupplier a supplier function that produces a message.
1240          *
1241          * @throws NullPointerException if {@code level} is {@code null},
1242          *         or {@code msgSupplier} is {@code null}.
1243          */
1244         public default void log(Level level, Supplier<String> msgSupplier) {
1245             Objects.requireNonNull(msgSupplier);
1246             if (isLoggable(Objects.requireNonNull(level))) {
1247                 log(level, (ResourceBundle) null, msgSupplier.get(), (Object[]) null);
1248             }
1249         }
1250 
1251         /**
1252          * Logs a message produced from the given object.
1253          *
1254          * If the logger is currently enabled for the given log message level then
1255          * a message is logged that, by default, is the result produced from
1256          * calling  toString on the given object.
1257          * Otherwise, the object is not operated on.
1258          *
1259          * @implSpec When logging is enabled for the given level, the default
1260          * implementation for this method calls
1261          * {@code this.log(level, (ResourceBundle)null, obj.toString(), (Object[])null);}
1262          *
1263          * @param level the log message level.
1264          * @param obj the object to log.
1265          *
1266          * @throws NullPointerException if {@code level} is {@code null}, or
1267          *         {@code obj} is {@code null}.
1268          */
1269         public default void log(Level level, Object obj) {
1270             Objects.requireNonNull(obj);
1271             if (isLoggable(Objects.requireNonNull(level))) {
1272                 this.log(level, (ResourceBundle) null, obj.toString(), (Object[]) null);
1273             }
1274         }
1275 
1276         /**
1277          * Logs a message associated with a given throwable.
1278          *
1279          * @implSpec The default implementation for this method calls
1280          * {@code this.log(level, (ResourceBundle)null, msg, thrown);}
1281          *
1282          * @param level the log message level.
1283          * @param msg the string message (or a key in the message catalog, if
1284          * this logger is a {@link
1285          * LoggerFinder#getLocalizedLogger(java.lang.String,
1286          * java.util.ResourceBundle, java.lang.Module) localized logger});
1287          * can be {@code null}.
1288          * @param thrown a {@code Throwable} associated with the log message;
1289          *        can be {@code null}.
1290          *
1291          * @throws NullPointerException if {@code level} is {@code null}.
1292          */
1293         public default void log(Level level, String msg, Throwable thrown) {
1294             this.log(level, null, msg, thrown);
1295         }
1296 
1297         /**
1298          * Logs a lazily supplied message associated with a given throwable.
1299          *
1300          * If the logger is currently enabled for the given log message level
1301          * then a message is logged that is the result produced by the
1302          * given supplier function.  Otherwise, the supplier is not operated on.
1303          *
1304          * @implSpec When logging is enabled for the given level, the default
1305          * implementation for this method calls
1306          * {@code this.log(level, (ResourceBundle)null, msgSupplier.get(), thrown);}
1307          *
1308          * @param level one of the log message level identifiers.
1309          * @param msgSupplier a supplier function that produces a message.
1310          * @param thrown a {@code Throwable} associated with log message;
1311          *               can be {@code null}.
1312          *
1313          * @throws NullPointerException if {@code level} is {@code null}, or
1314          *                               {@code msgSupplier} is {@code null}.
1315          */
1316         public default void log(Level level, Supplier<String> msgSupplier,
1317                 Throwable thrown) {
1318             Objects.requireNonNull(msgSupplier);
1319             if (isLoggable(Objects.requireNonNull(level))) {
1320                 this.log(level, null, msgSupplier.get(), thrown);
1321             }
1322         }
1323 
1324         /**
1325          * Logs a message with an optional list of parameters.
1326          *
1327          * @implSpec The default implementation for this method calls
1328          * {@code this.log(level, (ResourceBundle)null, format, params);}
1329          *
1330          * @param level one of the log message level identifiers.
1331          * @param format the string message format in {@link
1332          * java.text.MessageFormat} format, (or a key in the message
1333          * catalog, if this logger is a {@link
1334          * LoggerFinder#getLocalizedLogger(java.lang.String,
1335          * java.util.ResourceBundle, java.lang.Module) localized logger});
1336          * can be {@code null}.
1337          * @param params an optional list of parameters to the message (may be
1338          * none).
1339          *
1340          * @throws NullPointerException if {@code level} is {@code null}.
1341          */
1342         public default void log(Level level, String format, Object... params) {
1343             this.log(level, null, format, params);
1344         }
1345 
1346         /**
1347          * Logs a localized message associated with a given throwable.
1348          *
1349          * If the given resource bundle is non-{@code null},  the {@code msg}
1350          * string is localized using the given resource bundle.
1351          * Otherwise the {@code msg} string is not localized.
1352          *
1353          * @param level the log message level.
1354          * @param bundle a resource bundle to localize {@code msg}; can be
1355          * {@code null}.
1356          * @param msg the string message (or a key in the message catalog,
1357          *            if {@code bundle} is not {@code null}); can be {@code null}.
1358          * @param thrown a {@code Throwable} associated with the log message;
1359          *        can be {@code null}.
1360          *
1361          * @throws NullPointerException if {@code level} is {@code null}.
1362          */
1363         public void log(Level level, ResourceBundle bundle, String msg,
1364                 Throwable thrown);
1365 
1366         /**
1367          * Logs a message with resource bundle and an optional list of
1368          * parameters.
1369          *
1370          * If the given resource bundle is non-{@code null},  the {@code format}
1371          * string is localized using the given resource bundle.
1372          * Otherwise the {@code format} string is not localized.
1373          *
1374          * @param level the log message level.
1375          * @param bundle a resource bundle to localize {@code format}; can be
1376          * {@code null}.
1377          * @param format the string message format in {@link
1378          * java.text.MessageFormat} format, (or a key in the message
1379          * catalog if {@code bundle} is not {@code null}); can be {@code null}.
1380          * @param params an optional list of parameters to the message (may be
1381          * none).
1382          *
1383          * @throws NullPointerException if {@code level} is {@code null}.
1384          */
1385         public void log(Level level, ResourceBundle bundle, String format,
1386                 Object... params);
1387     }
1388 
1389     /**
1390      * The {@code LoggerFinder} service is responsible for creating, managing,
1391      * and configuring loggers to the underlying framework it uses.
1392      *
1393      * A logger finder is a concrete implementation of this class that has a
1394      * zero-argument constructor and implements the abstract methods defined
1395      * by this class.
1396      * The loggers returned from a logger finder are capable of routing log
1397      * messages to the logging backend this provider supports.
1398      * A given invocation of the Java Runtime maintains a single
1399      * system-wide LoggerFinder instance that is loaded as follows:
1400      * <ul>
1401      *    <li>First it finds any custom {@code LoggerFinder} provider
1402      *        using the {@link java.util.ServiceLoader} facility with the
1403      *        {@linkplain ClassLoader#getSystemClassLoader() system class
1404      *        loader}.</li>
1405      *    <li>If no {@code LoggerFinder} provider is found, the system default
1406      *        {@code LoggerFinder} implementation will be used.</li>
1407      * </ul>
1408      * <p>
1409      * An application can replace the logging backend
1410      * <i>even when the java.logging module is present</i>, by simply providing
1411      * and declaring an implementation of the {@link LoggerFinder} service.
1412      * <p>
1413      * <b>Default Implementation</b>
1414      * <p>
1415      * The system default {@code LoggerFinder} implementation uses
1416      * {@code java.util.logging} as the backend framework when the
1417      * {@code java.logging} module is present.
1418      * It returns a {@linkplain System.Logger logger} instance
1419      * that will route log messages to a {@link java.util.logging.Logger
1420      * java.util.logging.Logger}. Otherwise, if {@code java.logging} is not
1421      * present, the default implementation will return a simple logger
1422      * instance that will route log messages of {@code INFO} level and above to
1423      * the console ({@code System.err}).
1424      * <p>
1425      * <b>Logging Configuration</b>
1426      * <p>
1427      * {@linkplain Logger Logger} instances obtained from the
1428      * {@code LoggerFinder} factory methods are not directly configurable by
1429      * the application. Configuration is the responsibility of the underlying
1430      * logging backend, and usually requires using APIs specific to that backend.
1431      * <p>For the default {@code LoggerFinder} implementation
1432      * using {@code java.util.logging} as its backend, refer to
1433      * {@link java.util.logging java.util.logging} for logging configuration.
1434      * For the default {@code LoggerFinder} implementation returning simple loggers
1435      * when the {@code java.logging} module is absent, the configuration
1436      * is implementation dependent.
1437      * <p>
1438      * Usually an application that uses a logging framework will log messages
1439      * through a logger facade defined (or supported) by that framework.
1440      * Applications that wish to use an external framework should log
1441      * through the facade associated with that framework.
1442      * <p>
1443      * A system class that needs to log messages will typically obtain
1444      * a {@link System.Logger} instance to route messages to the logging
1445      * framework selected by the application.
1446      * <p>
1447      * Libraries and classes that only need loggers to produce log messages
1448      * should not attempt to configure loggers by themselves, as that
1449      * would make them dependent from a specific implementation of the
1450      * {@code LoggerFinder} service.
1451      * <p>
1452      * In addition, when a security manager is present, loggers provided to
1453      * system classes should not be directly configurable through the logging
1454      * backend without requiring permissions.
1455      * <br>
1456      * It is the responsibility of the provider of
1457      * the concrete {@code LoggerFinder} implementation to ensure that
1458      * these loggers are not configured by untrusted code without proper
1459      * permission checks, as configuration performed on such loggers usually
1460      * affects all applications in the same Java Runtime.
1461      * <p>
1462      * <b>Message Levels and Mapping to backend levels</b>
1463      * <p>
1464      * A logger finder is responsible for mapping from a {@code
1465      * System.Logger.Level} to a level supported by the logging backend it uses.
1466      * <br>The default LoggerFinder using {@code java.util.logging} as the backend
1467      * maps {@code System.Logger} levels to
1468      * {@linkplain java.util.logging.Level java.util.logging} levels
1469      * of corresponding severity - as described in {@link Logger.Level
1470      * Logger.Level}.
1471      *
1472      * @see java.lang.System
1473      * @see java.lang.System.Logger
1474      *
1475      * @since 9
1476      */
1477     public static abstract class LoggerFinder {
1478         /**
1479          * The {@code RuntimePermission("loggerFinder")} is
1480          * necessary to subclass and instantiate the {@code LoggerFinder} class,
1481          * as well as to obtain loggers from an instance of that class.
1482          */
1483         static final RuntimePermission LOGGERFINDER_PERMISSION =
1484                 new RuntimePermission("loggerFinder");
1485 
1486         /**
1487          * Creates a new instance of {@code LoggerFinder}.
1488          *
1489          * @implNote It is recommended that a {@code LoggerFinder} service
1490          *   implementation does not perform any heavy initialization in its
1491          *   constructor, in order to avoid possible risks of deadlock or class
1492          *   loading cycles during the instantiation of the service provider.
1493          *
1494          * @throws SecurityException if a security manager is present and its
1495          *         {@code checkPermission} method doesn't allow the
1496          *         {@code RuntimePermission("loggerFinder")}.
1497          */
1498         protected LoggerFinder() {
1499             this(checkPermission());
1500         }
1501 
1502         private LoggerFinder(Void unused) {
1503             // nothing to do.
1504         }
1505 
1506         private static Void checkPermission() {
1507             final SecurityManager sm = System.getSecurityManager();
1508             if (sm != null) {
1509                 sm.checkPermission(LOGGERFINDER_PERMISSION);
1510             }
1511             return null;
1512         }
1513 
1514         /**
1515          * Returns an instance of {@link Logger Logger}
1516          * for the given {@code module}.
1517          *
1518          * @param name the name of the logger.
1519          * @param module the module for which the logger is being requested.
1520          *
1521          * @return a {@link Logger logger} suitable for use within the given
1522          *         module.
1523          * @throws NullPointerException if {@code name} is {@code null} or
1524          *        {@code module} is {@code null}.
1525          * @throws SecurityException if a security manager is present and its
1526          *         {@code checkPermission} method doesn't allow the
1527          *         {@code RuntimePermission("loggerFinder")}.
1528          */
1529         public abstract Logger getLogger(String name, Module module);
1530 
1531         /**
1532          * Returns a localizable instance of {@link Logger Logger}
1533          * for the given {@code module}.
1534          * The returned logger will use the provided resource bundle for
1535          * message localization.
1536          *
1537          * @implSpec By default, this method calls {@link
1538          * #getLogger(java.lang.String, java.lang.Module)
1539          * this.getLogger(name, module)} to obtain a logger, then wraps that
1540          * logger in a {@link Logger} instance where all methods that do not
1541          * take a {@link ResourceBundle} as parameter are redirected to one
1542          * which does - passing the given {@code bundle} for
1543          * localization. So for instance, a call to {@link
1544          * Logger#log(Logger.Level, String) Logger.log(Level.INFO, msg)}
1545          * will end up as a call to {@link
1546          * Logger#log(Logger.Level, ResourceBundle, String, Object...)
1547          * Logger.log(Level.INFO, bundle, msg, (Object[])null)} on the wrapped
1548          * logger instance.
1549          * Note however that by default, string messages returned by {@link
1550          * java.util.function.Supplier Supplier&lt;String&gt;} will not be
1551          * localized, as it is assumed that such strings are messages which are
1552          * already constructed, rather than keys in a resource bundle.
1553          * <p>
1554          * An implementation of {@code LoggerFinder} may override this method,
1555          * for example, when the underlying logging backend provides its own
1556          * mechanism for localizing log messages, then such a
1557          * {@code LoggerFinder} would be free to return a logger
1558          * that makes direct use of the mechanism provided by the backend.
1559          *
1560          * @param name    the name of the logger.
1561          * @param bundle  a resource bundle; can be {@code null}.
1562          * @param module  the module for which the logger is being requested.
1563          * @return an instance of {@link Logger Logger}  which will use the
1564          * provided resource bundle for message localization.
1565          *
1566          * @throws NullPointerException if {@code name} is {@code null} or
1567          *         {@code module} is {@code null}.
1568          * @throws SecurityException if a security manager is present and its
1569          *         {@code checkPermission} method doesn't allow the
1570          *         {@code RuntimePermission("loggerFinder")}.
1571          */
1572         public Logger getLocalizedLogger(String name, ResourceBundle bundle,
1573                                          Module module) {
1574             return new LocalizedLoggerWrapper<>(getLogger(name, module), bundle);
1575         }
1576 
1577         /**
1578          * Returns the {@code LoggerFinder} instance. There is one
1579          * single system-wide {@code LoggerFinder} instance in
1580          * the Java Runtime.  See the class specification of how the
1581          * {@link LoggerFinder LoggerFinder} implementation is located and
1582          * loaded.
1583 
1584          * @return the {@link LoggerFinder LoggerFinder} instance.
1585          * @throws SecurityException if a security manager is present and its
1586          *         {@code checkPermission} method doesn't allow the
1587          *         {@code RuntimePermission("loggerFinder")}.
1588          */
1589         public static LoggerFinder getLoggerFinder() {
1590             final SecurityManager sm = System.getSecurityManager();
1591             if (sm != null) {
1592                 sm.checkPermission(LOGGERFINDER_PERMISSION);
1593             }
1594             return accessProvider();
1595         }
1596 
1597 
1598         private static volatile LoggerFinder service;
1599         static LoggerFinder accessProvider() {
1600             // We do not need to synchronize: LoggerFinderLoader will
1601             // always return the same instance, so if we don't have it,
1602             // just fetch it again.
1603             if (service == null) {
1604                 PrivilegedAction<LoggerFinder> pa =
1605                         () -> LoggerFinderLoader.getLoggerFinder();
1606                 service = AccessController.doPrivileged(pa, null,
1607                         LOGGERFINDER_PERMISSION);
1608             }
1609             return service;
1610         }
1611 
1612     }
1613 
1614 
1615     /**
1616      * Returns an instance of {@link Logger Logger} for the caller's
1617      * use.
1618      *
1619      * @implSpec
1620      * Instances returned by this method route messages to loggers
1621      * obtained by calling {@link LoggerFinder#getLogger(java.lang.String,
1622      * java.lang.Module) LoggerFinder.getLogger(name, module)}, where
1623      * {@code module} is the caller's module.
1624      * In cases where {@code System.getLogger} is called from a context where
1625      * there is no caller frame on the stack (e.g when called directly
1626      * from a JNI attached thread), {@code IllegalCallerException} is thrown.
1627      * To obtain a logger in such a context, use an auxiliary class that will
1628      * implicitly be identified as the caller, or use the system {@link
1629      * LoggerFinder#getLoggerFinder() LoggerFinder} to obtain a logger instead.
1630      * Note that doing the latter may eagerly initialize the underlying
1631      * logging system.
1632      *
1633      * @apiNote
1634      * This method may defer calling the {@link
1635      * LoggerFinder#getLogger(java.lang.String, java.lang.Module)
1636      * LoggerFinder.getLogger} method to create an actual logger supplied by
1637      * the logging backend, for instance, to allow loggers to be obtained during
1638      * the system initialization time.
1639      *
1640      * @param name the name of the logger.
1641      * @return an instance of {@link Logger} that can be used by the calling
1642      *         class.
1643      * @throws NullPointerException if {@code name} is {@code null}.
1644      * @throws IllegalCallerException if there is no Java caller frame on the
1645      *         stack.
1646      *
1647      * @since 9
1648      */
1649     @CallerSensitive
1650     public static Logger getLogger(String name) {
1651         Objects.requireNonNull(name);
1652         final Class<?> caller = Reflection.getCallerClass();
1653         if (caller == null) {
1654             throw new IllegalCallerException("no caller frame");
1655         }
1656         return LazyLoggers.getLogger(name, caller.getModule());
1657     }
1658 
1659     /**
1660      * Returns a localizable instance of {@link Logger
1661      * Logger} for the caller's use.
1662      * The returned logger will use the provided resource bundle for message
1663      * localization.
1664      *
1665      * @implSpec
1666      * The returned logger will perform message localization as specified
1667      * by {@link LoggerFinder#getLocalizedLogger(java.lang.String,
1668      * java.util.ResourceBundle, java.lang.Module)
1669      * LoggerFinder.getLocalizedLogger(name, bundle, module)}, where
1670      * {@code module} is the caller's module.
1671      * In cases where {@code System.getLogger} is called from a context where
1672      * there is no caller frame on the stack (e.g when called directly
1673      * from a JNI attached thread), {@code IllegalCallerException} is thrown.
1674      * To obtain a logger in such a context, use an auxiliary class that
1675      * will implicitly be identified as the caller, or use the system {@link
1676      * LoggerFinder#getLoggerFinder() LoggerFinder} to obtain a logger instead.
1677      * Note that doing the latter may eagerly initialize the underlying
1678      * logging system.
1679      *
1680      * @apiNote
1681      * This method is intended to be used after the system is fully initialized.
1682      * This method may trigger the immediate loading and initialization
1683      * of the {@link LoggerFinder} service, which may cause issues if the
1684      * Java Runtime is not ready to initialize the concrete service
1685      * implementation yet.
1686      * System classes which may be loaded early in the boot sequence and
1687      * need to log localized messages should create a logger using
1688      * {@link #getLogger(java.lang.String)} and then use the log methods that
1689      * take a resource bundle as parameter.
1690      *
1691      * @param name    the name of the logger.
1692      * @param bundle  a resource bundle.
1693      * @return an instance of {@link Logger} which will use the provided
1694      * resource bundle for message localization.
1695      * @throws NullPointerException if {@code name} is {@code null} or
1696      *         {@code bundle} is {@code null}.
1697      * @throws IllegalCallerException if there is no Java caller frame on the
1698      *         stack.
1699      *
1700      * @since 9
1701      */
1702     @CallerSensitive
1703     public static Logger getLogger(String name, ResourceBundle bundle) {
1704         final ResourceBundle rb = Objects.requireNonNull(bundle);
1705         Objects.requireNonNull(name);
1706         final Class<?> caller = Reflection.getCallerClass();
1707         if (caller == null) {
1708             throw new IllegalCallerException("no caller frame");
1709         }
1710         final SecurityManager sm = System.getSecurityManager();
1711         // We don't use LazyLoggers if a resource bundle is specified.
1712         // Bootstrap sensitive classes in the JDK do not use resource bundles
1713         // when logging. This could be revisited later, if it needs to.
1714         if (sm != null) {
1715             final PrivilegedAction<Logger> pa =
1716                     () -> LoggerFinder.accessProvider()
1717                             .getLocalizedLogger(name, rb, caller.getModule());
1718             return AccessController.doPrivileged(pa, null,
1719                                          LoggerFinder.LOGGERFINDER_PERMISSION);
1720         }
1721         return LoggerFinder.accessProvider()
1722                 .getLocalizedLogger(name, rb, caller.getModule());
1723     }
1724 
1725     /**
1726      * Terminates the currently running Java Virtual Machine. The
1727      * argument serves as a status code; by convention, a nonzero status
1728      * code indicates abnormal termination.
1729      * <p>
1730      * This method calls the {@code exit} method in class
1731      * {@code Runtime}. This method never returns normally.
1732      * <p>
1733      * The call {@code System.exit(n)} is effectively equivalent to
1734      * the call:
1735      * <blockquote><pre>
1736      * Runtime.getRuntime().exit(n)
1737      * </pre></blockquote>
1738      *
1739      * @param      status   exit status.
1740      * @throws  SecurityException
1741      *        if a security manager exists and its {@code checkExit}
1742      *        method doesn't allow exit with the specified status.
1743      * @see        java.lang.Runtime#exit(int)
1744      */
1745     public static void exit(int status) {
1746         Runtime.getRuntime().exit(status);
1747     }
1748 
1749     /**
1750      * Runs the garbage collector.
1751      *
1752      * Calling the {@code gc} method suggests that the Java Virtual
1753      * Machine expend effort toward recycling unused objects in order to
1754      * make the memory they currently occupy available for quick reuse.
1755      * When control returns from the method call, the Java Virtual
1756      * Machine has made a best effort to reclaim space from all discarded
1757      * objects.
1758      * <p>
1759      * The call {@code System.gc()} is effectively equivalent to the
1760      * call:
1761      * <blockquote><pre>
1762      * Runtime.getRuntime().gc()
1763      * </pre></blockquote>
1764      *
1765      * @see     java.lang.Runtime#gc()
1766      */
1767     public static void gc() {
1768         Runtime.getRuntime().gc();
1769     }
1770 
1771     /**
1772      * Runs the finalization methods of any objects pending finalization.
1773      *
1774      * Calling this method suggests that the Java Virtual Machine expend
1775      * effort toward running the {@code finalize} methods of objects
1776      * that have been found to be discarded but whose {@code finalize}
1777      * methods have not yet been run. When control returns from the
1778      * method call, the Java Virtual Machine has made a best effort to
1779      * complete all outstanding finalizations.
1780      * <p>
1781      * The call {@code System.runFinalization()} is effectively
1782      * equivalent to the call:
1783      * <blockquote><pre>
1784      * Runtime.getRuntime().runFinalization()
1785      * </pre></blockquote>
1786      *
1787      * @see     java.lang.Runtime#runFinalization()
1788      */
1789     public static void runFinalization() {
1790         Runtime.getRuntime().runFinalization();
1791     }
1792 
1793     /**
1794      * Loads the native library specified by the filename argument.  The filename
1795      * argument must be an absolute path name.
1796      *
1797      * If the filename argument, when stripped of any platform-specific library
1798      * prefix, path, and file extension, indicates a library whose name is,
1799      * for example, L, and a native library called L is statically linked
1800      * with the VM, then the JNI_OnLoad_L function exported by the library
1801      * is invoked rather than attempting to load a dynamic library.
1802      * A filename matching the argument does not have to exist in the
1803      * file system.
1804      * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
1805      * for more details.
1806      *
1807      * Otherwise, the filename argument is mapped to a native library image in
1808      * an implementation-dependent manner.
1809      *
1810      * <p>
1811      * The call {@code System.load(name)} is effectively equivalent
1812      * to the call:
1813      * <blockquote><pre>
1814      * Runtime.getRuntime().load(name)
1815      * </pre></blockquote>
1816      *
1817      * @param      filename   the file to load.
1818      * @throws     SecurityException  if a security manager exists and its
1819      *             {@code checkLink} method doesn't allow
1820      *             loading of the specified dynamic library
1821      * @throws     UnsatisfiedLinkError  if either the filename is not an
1822      *             absolute path name, the native library is not statically
1823      *             linked with the VM, or the library cannot be mapped to
1824      *             a native library image by the host system.
1825      * @throws     NullPointerException if {@code filename} is {@code null}
1826      * @see        java.lang.Runtime#load(java.lang.String)
1827      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
1828      */
1829     @CallerSensitive
1830     public static void load(String filename) {
1831         Runtime.getRuntime().load0(Reflection.getCallerClass(), filename);
1832     }
1833 
1834     /**
1835      * Loads the native library specified by the {@code libname}
1836      * argument.  The {@code libname} argument must not contain any platform
1837      * specific prefix, file extension or path. If a native library
1838      * called {@code libname} is statically linked with the VM, then the
1839      * JNI_OnLoad_{@code libname} function exported by the library is invoked.
1840      * See the <a href="{@docRoot}/../specs/jni/index.html"> JNI Specification</a>
1841      * for more details.
1842      *
1843      * Otherwise, the libname argument is loaded from a system library
1844      * location and mapped to a native library image in an implementation-
1845      * dependent manner.
1846      * <p>
1847      * The call {@code System.loadLibrary(name)} is effectively
1848      * equivalent to the call
1849      * <blockquote><pre>
1850      * Runtime.getRuntime().loadLibrary(name)
1851      * </pre></blockquote>
1852      *
1853      * @param      libname   the name of the library.
1854      * @throws     SecurityException  if a security manager exists and its
1855      *             {@code checkLink} method doesn't allow
1856      *             loading of the specified dynamic library
1857      * @throws     UnsatisfiedLinkError if either the libname argument
1858      *             contains a file path, the native library is not statically
1859      *             linked with the VM,  or the library cannot be mapped to a
1860      *             native library image by the host system.
1861      * @throws     NullPointerException if {@code libname} is {@code null}
1862      * @see        java.lang.Runtime#loadLibrary(java.lang.String)
1863      * @see        java.lang.SecurityManager#checkLink(java.lang.String)
1864      */
1865     @CallerSensitive
1866     public static void loadLibrary(String libname) {
1867         Runtime.getRuntime().loadLibrary0(Reflection.getCallerClass(), libname);
1868     }
1869 
1870     /**
1871      * Maps a library name into a platform-specific string representing
1872      * a native library.
1873      *
1874      * @param      libname the name of the library.
1875      * @return     a platform-dependent native library name.
1876      * @throws     NullPointerException if {@code libname} is {@code null}
1877      * @see        java.lang.System#loadLibrary(java.lang.String)
1878      * @see        java.lang.ClassLoader#findLibrary(java.lang.String)
1879      * @since      1.2
1880      */
1881     public static native String mapLibraryName(String libname);
1882 
1883     /**
1884      * Create PrintStream for stdout/err based on encoding.
1885      */
1886     private static PrintStream newPrintStream(FileOutputStream fos, String enc) {
1887        if (enc != null) {
1888             try {
1889                 return new PrintStream(new BufferedOutputStream(fos, 128), true, enc);
1890             } catch (UnsupportedEncodingException uee) {}
1891         }
1892         return new PrintStream(new BufferedOutputStream(fos, 128), true);
1893     }
1894 
1895     /**
1896      * Logs an exception/error at initialization time to stdout or stderr.
1897      *
1898      * @param printToStderr to print to stderr rather than stdout
1899      * @param printStackTrace to print the stack trace
1900      * @param msg the message to print before the exception, can be {@code null}
1901      * @param e the exception or error
1902      */
1903     private static void logInitException(boolean printToStderr,
1904                                          boolean printStackTrace,
1905                                          String msg,
1906                                          Throwable e) {
1907         if (VM.initLevel() < 1) {
1908             throw new InternalError("system classes not initialized");
1909         }
1910         PrintStream log = (printToStderr) ? err : out;
1911         if (msg != null) {
1912             log.println(msg);
1913         }
1914         if (printStackTrace) {
1915             e.printStackTrace(log);
1916         } else {
1917             log.println(e);
1918             for (Throwable suppressed : e.getSuppressed()) {
1919                 log.println("Suppressed: " + suppressed);
1920             }
1921             Throwable cause = e.getCause();
1922             if (cause != null) {
1923                 log.println("Caused by: " + cause);
1924             }
1925         }
1926     }
1927 
1928     /**
1929      * Initialize the system class.  Called after thread initialization.
1930      */
1931     private static void initPhase1() {
1932 
1933         // VM might invoke JNU_NewStringPlatform() to set those encoding
1934         // sensitive properties (user.home, user.name, boot.class.path, etc.)
1935         // during "props" initialization, in which it may need access, via
1936         // System.getProperty(), to the related system encoding property that
1937         // have been initialized (put into "props") at early stage of the
1938         // initialization. So make sure the "props" is available at the
1939         // very beginning of the initialization and all system properties to
1940         // be put into it directly.
1941         props = new Properties(84);
1942         initProperties(props);  // initialized by the VM
1943 
1944         // There are certain system configurations that may be controlled by
1945         // VM options such as the maximum amount of direct memory and
1946         // Integer cache size used to support the object identity semantics
1947         // of autoboxing.  Typically, the library will obtain these values
1948         // from the properties set by the VM.  If the properties are for
1949         // internal implementation use only, these properties should be
1950         // removed from the system properties.
1951         //
1952         // See java.lang.Integer.IntegerCache and the
1953         // VM.saveAndRemoveProperties method for example.
1954         //
1955         // Save a private copy of the system properties object that
1956         // can only be accessed by the internal implementation.  Remove
1957         // certain system properties that are not intended for public access.
1958         VM.saveAndRemoveProperties(props);
1959 
1960         lineSeparator = props.getProperty("line.separator");
1961         StaticProperty.javaHome();          // Load StaticProperty to cache the property values
1962         VersionProps.init();
1963 
1964         FileInputStream fdIn = new FileInputStream(FileDescriptor.in);
1965         FileOutputStream fdOut = new FileOutputStream(FileDescriptor.out);
1966         FileOutputStream fdErr = new FileOutputStream(FileDescriptor.err);
1967         setIn0(new BufferedInputStream(fdIn));
1968         setOut0(newPrintStream(fdOut, props.getProperty("sun.stdout.encoding")));
1969         setErr0(newPrintStream(fdErr, props.getProperty("sun.stderr.encoding")));
1970 
1971         // Setup Java signal handlers for HUP, TERM, and INT (where available).
1972         Terminator.setup();
1973 
1974         // Initialize any miscellaneous operating system settings that need to be
1975         // set for the class libraries. Currently this is no-op everywhere except
1976         // for Windows where the process-wide error mode is set before the java.io
1977         // classes are used.
1978         VM.initializeOSEnvironment();
1979 
1980         // The main thread is not added to its thread group in the same
1981         // way as other threads; we must do it ourselves here.
1982         Thread current = Thread.currentThread();
1983         current.getThreadGroup().add(current);
1984 
1985         // register shared secrets
1986         setJavaLangAccess();
1987 
1988         // Subsystems that are invoked during initialization can invoke
1989         // VM.isBooted() in order to avoid doing things that should
1990         // wait until the VM is fully initialized. The initialization level
1991         // is incremented from 0 to 1 here to indicate the first phase of
1992         // initialization has completed.
1993         // IMPORTANT: Ensure that this remains the last initialization action!
1994         VM.initLevel(1);
1995     }
1996 
1997     // @see #initPhase2()
1998     static ModuleLayer bootLayer;
1999 
2000     /*
2001      * Invoked by VM.  Phase 2 module system initialization.
2002      * Only classes in java.base can be loaded in this phase.
2003      *
2004      * @param printToStderr print exceptions to stderr rather than stdout
2005      * @param printStackTrace print stack trace when exception occurs
2006      *
2007      * @return JNI_OK for success, JNI_ERR for failure
2008      */
2009     private static int initPhase2(boolean printToStderr, boolean printStackTrace) {
2010         try {
2011             bootLayer = ModuleBootstrap.boot();
2012         } catch (Exception | Error e) {
2013             logInitException(printToStderr, printStackTrace,
2014                              "Error occurred during initialization of boot layer", e);
2015             return -1; // JNI_ERR
2016         }
2017 
2018         // module system initialized
2019         VM.initLevel(2);
2020 
2021         return 0; // JNI_OK
2022     }
2023 
2024     /*
2025      * Invoked by VM.  Phase 3 is the final system initialization:
2026      * 1. set security manager
2027      * 2. set system class loader
2028      * 3. set TCCL
2029      *
2030      * This method must be called after the module system initialization.
2031      * The security manager and system class loader may be custom class from
2032      * the application classpath or modulepath.
2033      */
2034     private static void initPhase3() {
2035         // set security manager
2036         String cn = System.getProperty("java.security.manager");
2037         if (cn != null) {
2038             if (cn.isEmpty() || "default".equals(cn)) {
2039                 System.setSecurityManager(new SecurityManager());
2040             } else {
2041                 try {
2042                     Class<?> c = Class.forName(cn, false, ClassLoader.getBuiltinAppClassLoader());
2043                     Constructor<?> ctor = c.getConstructor();
2044                     // Must be a public subclass of SecurityManager with
2045                     // a public no-arg constructor
2046                     if (!SecurityManager.class.isAssignableFrom(c) ||
2047                             !Modifier.isPublic(c.getModifiers()) ||
2048                             !Modifier.isPublic(ctor.getModifiers())) {
2049                         throw new Error("Could not create SecurityManager: " + ctor.toString());
2050                     }
2051                     // custom security manager implementation may be in unnamed module
2052                     // or a named module but non-exported package
2053                     ctor.setAccessible(true);
2054                     SecurityManager sm = (SecurityManager) ctor.newInstance();
2055                     System.setSecurityManager(sm);
2056                 } catch (Exception e) {
2057                     throw new Error("Could not create SecurityManager", e);
2058                 }
2059             }
2060         }
2061 
2062         // initializing the system class loader
2063         VM.initLevel(3);
2064 
2065         // system class loader initialized
2066         ClassLoader scl = ClassLoader.initSystemClassLoader();
2067 
2068         // set TCCL
2069         Thread.currentThread().setContextClassLoader(scl);
2070 
2071         // system is fully initialized
2072         VM.initLevel(4);
2073     }
2074 
2075     private static void setJavaLangAccess() {
2076         // Allow privileged classes outside of java.lang
2077         SharedSecrets.setJavaLangAccess(new JavaLangAccess() {
2078             public List<Method> getDeclaredPublicMethods(Class<?> klass, String name, Class<?>... parameterTypes) {
2079                 return klass.getDeclaredPublicMethods(name, parameterTypes);
2080             }
2081             public jdk.internal.reflect.ConstantPool getConstantPool(Class<?> klass) {
2082                 return klass.getConstantPool();
2083             }
2084             public boolean casAnnotationType(Class<?> klass, AnnotationType oldType, AnnotationType newType) {
2085                 return klass.casAnnotationType(oldType, newType);
2086             }
2087             public AnnotationType getAnnotationType(Class<?> klass) {
2088                 return klass.getAnnotationType();
2089             }
2090             public Map<Class<? extends Annotation>, Annotation> getDeclaredAnnotationMap(Class<?> klass) {
2091                 return klass.getDeclaredAnnotationMap();
2092             }
2093             public byte[] getRawClassAnnotations(Class<?> klass) {
2094                 return klass.getRawAnnotations();
2095             }
2096             public byte[] getRawClassTypeAnnotations(Class<?> klass) {
2097                 return klass.getRawTypeAnnotations();
2098             }
2099             public byte[] getRawExecutableTypeAnnotations(Executable executable) {
2100                 return Class.getExecutableTypeAnnotationBytes(executable);
2101             }
2102             public <E extends Enum<E>>
2103             E[] getEnumConstantsShared(Class<E> klass) {
2104                 return klass.getEnumConstantsShared();
2105             }
2106             public void blockedOn(Interruptible b) {
2107                 Thread.blockedOn(b);
2108             }
2109             public void registerShutdownHook(int slot, boolean registerShutdownInProgress, Runnable hook) {
2110                 Shutdown.add(slot, registerShutdownInProgress, hook);
2111             }
2112             public Thread newThreadWithAcc(Runnable target, AccessControlContext acc) {
2113                 return new Thread(target, acc);
2114             }
2115             @SuppressWarnings("deprecation")
2116             public void invokeFinalize(Object o) throws Throwable {
2117                 o.finalize();
2118             }
2119             public ConcurrentHashMap<?, ?> createOrGetClassLoaderValueMap(ClassLoader cl) {
2120                 return cl.createOrGetClassLoaderValueMap();
2121             }
2122             public Class<?> defineClass(ClassLoader loader, String name, byte[] b, ProtectionDomain pd, String source) {
2123                 return ClassLoader.defineClass1(loader, name, b, 0, b.length, pd, source);
2124             }
2125             public Class<?> findBootstrapClassOrNull(ClassLoader cl, String name) {
2126                 return cl.findBootstrapClassOrNull(name);
2127             }
2128             public Package definePackage(ClassLoader cl, String name, Module module) {
2129                 return cl.definePackage(name, module);
2130             }
2131             public String fastUUID(long lsb, long msb) {
2132                 return Long.fastUUID(lsb, msb);
2133             }
2134             public void addNonExportedPackages(ModuleLayer layer) {
2135                 SecurityManager.addNonExportedPackages(layer);
2136             }
2137             public void invalidatePackageAccessCache() {
2138                 SecurityManager.invalidatePackageAccessCache();
2139             }
2140             public Module defineModule(ClassLoader loader,
2141                                        ModuleDescriptor descriptor,
2142                                        URI uri) {
2143                 return new Module(null, loader, descriptor, uri);
2144             }
2145             public Module defineUnnamedModule(ClassLoader loader) {
2146                 return new Module(loader);
2147             }
2148             public void addReads(Module m1, Module m2) {
2149                 m1.implAddReads(m2);
2150             }
2151             public void addReadsAllUnnamed(Module m) {
2152                 m.implAddReadsAllUnnamed();
2153             }
2154             public void addExports(Module m, String pn, Module other) {
2155                 m.implAddExports(pn, other);
2156             }
2157             public void addExportsToAllUnnamed(Module m, String pn) {
2158                 m.implAddExportsToAllUnnamed(pn);
2159             }
2160             public void addOpens(Module m, String pn, Module other) {
2161                 m.implAddOpens(pn, other);
2162             }
2163             public void addOpensToAllUnnamed(Module m, String pn) {
2164                 m.implAddOpensToAllUnnamed(pn);
2165             }
2166             public void addOpensToAllUnnamed(Module m, Iterator<String> packages) {
2167                 m.implAddOpensToAllUnnamed(packages);
2168             }
2169             public void addUses(Module m, Class<?> service) {
2170                 m.implAddUses(service);
2171             }
2172             public boolean isReflectivelyExported(Module m, String pn, Module other) {
2173                 return m.isReflectivelyExported(pn, other);
2174             }
2175             public boolean isReflectivelyOpened(Module m, String pn, Module other) {
2176                 return m.isReflectivelyOpened(pn, other);
2177             }
2178             public ServicesCatalog getServicesCatalog(ModuleLayer layer) {
2179                 return layer.getServicesCatalog();
2180             }
2181             public Stream<ModuleLayer> layers(ModuleLayer layer) {
2182                 return layer.layers();
2183             }
2184             public Stream<ModuleLayer> layers(ClassLoader loader) {
2185                 return ModuleLayer.layers(loader);
2186             }
2187 
2188             public String newStringNoRepl(byte[] bytes, Charset cs) throws CharacterCodingException  {
2189                 return StringCoding.newStringNoRepl(bytes, cs);
2190             }
2191 
2192             public byte[] getBytesNoRepl(String s, Charset cs) throws CharacterCodingException {
2193                 return StringCoding.getBytesNoRepl(s, cs);
2194             }
2195 
2196             public String newStringUTF8NoRepl(byte[] bytes, int off, int len) {
2197                 return StringCoding.newStringUTF8NoRepl(bytes, off, len);
2198             }
2199 
2200             public byte[] getBytesUTF8NoRepl(String s) {
2201                 return StringCoding.getBytesUTF8NoRepl(s);
2202             }
2203 
2204         });
2205     }
2206 }