1 /*
   2  * Copyright (c) 2000, 2016, 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 
  26 package java.lang;
  27 
  28 import jdk.internal.loader.BuiltinClassLoader;
  29 import jdk.internal.misc.SharedSecrets;
  30 import jdk.internal.misc.VM;
  31 import jdk.internal.module.ModuleHashes;
  32 
  33 import java.lang.reflect.Layer;
  34 import java.lang.reflect.Module;
  35 import java.util.HashSet;
  36 import java.util.Objects;
  37 import java.util.Optional;
  38 import java.util.Set;
  39 
  40 /**
  41  * An element in a stack trace, as returned by {@link
  42  * Throwable#getStackTrace()}.  Each element represents a single stack frame.
  43  * All stack frames except for the one at the top of the stack represent
  44  * a method invocation.  The frame at the top of the stack represents the
  45  * execution point at which the stack trace was generated.  Typically,
  46  * this is the point at which the throwable corresponding to the stack trace
  47  * was created.
  48  *
  49  * @since  1.4
  50  * @author Josh Bloch
  51  */
  52 public final class StackTraceElement implements java.io.Serializable {
  53 
  54     // For Throwables and StackWalker, the VM initially sets this field to a
  55     // reference to the declaring Class.  The Class reference is used to 
  56     // construct the 'format' bitmap, and then is cleared.
  57     //
  58     // For STEs constructed using the public constructors, this field is not used.
  59     private transient Class<?> declaringClassObject;
  60 
  61     // Normally initialized by VM
  62     private String classLoaderName;
  63     private String moduleName;
  64     private String moduleVersion;
  65     private String declaringClass;
  66     private String methodName;
  67     private String fileName;
  68     private int    lineNumber;
  69     private byte   format = 0; // Default to show all
  70 
  71     /**
  72      * Creates a stack trace element representing the specified execution
  73      * point. The {@link #getModuleName module name} and {@link
  74      * #getModuleVersion module version} of the stack trace element will
  75      * be {@code null}.
  76      *
  77      * @param declaringClass the fully qualified name of the class containing
  78      *        the execution point represented by the stack trace element
  79      * @param methodName the name of the method containing the execution point
  80      *        represented by the stack trace element
  81      * @param fileName the name of the file containing the execution point
  82      *         represented by the stack trace element, or {@code null} if
  83      *         this information is unavailable
  84      * @param lineNumber the line number of the source line containing the
  85      *         execution point represented by this stack trace element, or
  86      *         a negative number if this information is unavailable. A value
  87      *         of -2 indicates that the method containing the execution point
  88      *         is a native method
  89      * @throws NullPointerException if {@code declaringClass} or
  90      *         {@code methodName} is null
  91      * @since 1.5
  92      */
  93     public StackTraceElement(String declaringClass, String methodName,
  94                              String fileName, int lineNumber) {
  95         this(null, null, null, declaringClass, methodName, fileName, lineNumber);
  96     }
  97 
  98     /**
  99      * Creates a stack trace element representing the specified execution
 100      * point.
 101      *
 102      * @param classLoaderName the class loader name if the class loader of
 103      *        the class containing the execution point represented by
 104      *        the stack trace is named; otherwise {@code null}
 105      * @param moduleName the module name if the class containing the
 106      *        execution point represented by the stack trace is in a named
 107      *        module; otherwise {@code null}
 108      * @param moduleVersion the module version if the class containing the
 109      *        execution point represented by the stack trace is in a named
 110      *        module that has a version; otherwise {@code null}
 111      * @param declaringClass the fully qualified name of the class containing
 112      *        the execution point represented by the stack trace element
 113      * @param methodName the name of the method containing the execution point
 114      *        represented by the stack trace element
 115      * @param fileName the name of the file containing the execution point
 116      *        represented by the stack trace element, or {@code null} if
 117      *        this information is unavailable
 118      * @param lineNumber the line number of the source line containing the
 119      *        execution point represented by this stack trace element, or
 120      *        a negative number if this information is unavailable. A value
 121      *        of -2 indicates that the method containing the execution point
 122      *        is a native method
 123      *
 124      * @throws NullPointerException if {@code declaringClass} is {@code null}
 125      *         or {@code methodName} is {@code null}
 126      *
 127      * @since 9
 128      */
 129     public StackTraceElement(String classLoaderName,
 130                              String moduleName, String moduleVersion,
 131                              String declaringClass, String methodName,
 132                              String fileName, int lineNumber) {
 133         this.classLoaderName = classLoaderName;
 134         this.moduleName      = moduleName;
 135         this.moduleVersion   = moduleVersion;
 136         this.declaringClass  = Objects.requireNonNull(declaringClass, "Declaring class is null");
 137         this.methodName      = Objects.requireNonNull(methodName, "Method name is null");
 138         this.fileName        = fileName;
 139         this.lineNumber      = lineNumber;
 140     }
 141 
 142     /*
 143      * Private constructor for the factory methods to create StackTraceElement
 144      * for Throwable and StackFrameInfo
 145      */
 146     private StackTraceElement() {}
 147 
 148     /**
 149      * Returns the name of the source file containing the execution point
 150      * represented by this stack trace element.  Generally, this corresponds
 151      * to the {@code SourceFile} attribute of the relevant {@code class}
 152      * file (as per <i>The Java Virtual Machine Specification</i>, Section
 153      * 4.7.7).  In some systems, the name may refer to some source code unit
 154      * other than a file, such as an entry in source repository.
 155      *
 156      * @return the name of the file containing the execution point
 157      *         represented by this stack trace element, or {@code null} if
 158      *         this information is unavailable.
 159      */
 160     public String getFileName() {
 161         return fileName;
 162     }
 163 
 164     /**
 165      * Returns the line number of the source line containing the execution
 166      * point represented by this stack trace element.  Generally, this is
 167      * derived from the {@code LineNumberTable} attribute of the relevant
 168      * {@code class} file (as per <i>The Java Virtual Machine
 169      * Specification</i>, Section 4.7.8).
 170      *
 171      * @return the line number of the source line containing the execution
 172      *         point represented by this stack trace element, or a negative
 173      *         number if this information is unavailable.
 174      */
 175     public int getLineNumber() {
 176         return lineNumber;
 177     }
 178 
 179     /**
 180      * Returns the module name of the module containing the execution point
 181      * represented by this stack trace element.
 182      *
 183      * @return the module name of the {@code Module} containing the execution
 184      *         point represented by this stack trace element; {@code null}
 185      *         if the module name is not available.
 186      * @since 9
 187      * @see java.lang.reflect.Module#getName()
 188      */
 189     public String getModuleName() {
 190         return moduleName;
 191     }
 192 
 193     /**
 194      * Returns the module version of the module containing the execution point
 195      * represented by this stack trace element.
 196      *
 197      * @return the module version of the {@code Module} containing the execution
 198      *         point represented by this stack trace element; {@code null}
 199      *         if the module version is not available.
 200      * @since 9
 201      * @see java.lang.module.ModuleDescriptor.Version
 202      */
 203     public String getModuleVersion() {
 204         return moduleVersion;
 205     }
 206 
 207     /**
 208      * Returns the name of the class loader of the class containing the
 209      * execution point represented by this stack trace element.
 210      *
 211      * @return the name of the class loader of the class containing the execution
 212      *         point represented by this stack trace element; {@code null}
 213      *         if the class loader is not named.
 214      *
 215      * @since 9
 216      * @see java.lang.ClassLoader#getName()
 217      */
 218     public String getClassLoaderName() {
 219         return classLoaderName;
 220     }
 221 
 222     /**
 223      * Returns the fully qualified name of the class containing the
 224      * execution point represented by this stack trace element.
 225      *
 226      * @return the fully qualified name of the {@code Class} containing
 227      *         the execution point represented by this stack trace element.
 228      */
 229     public String getClassName() {
 230         return declaringClass;
 231     }
 232 
 233     /**
 234      * Returns the name of the method containing the execution point
 235      * represented by this stack trace element.  If the execution point is
 236      * contained in an instance or class initializer, this method will return
 237      * the appropriate <i>special method name</i>, {@code <init>} or
 238      * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual
 239      * Machine Specification</i>.
 240      *
 241      * @return the name of the method containing the execution point
 242      *         represented by this stack trace element.
 243      */
 244     public String getMethodName() {
 245         return methodName;
 246     }
 247 
 248     /**
 249      * Returns true if the method containing the execution point
 250      * represented by this stack trace element is a native method.
 251      *
 252      * @return {@code true} if the method containing the execution point
 253      *         represented by this stack trace element is a native method.
 254      */
 255     public boolean isNativeMethod() {
 256         return lineNumber == -2;
 257     }
 258 
 259     /**
 260      * Returns a string representation of this stack trace element.
 261      * 
 262      * @apiNote The format of this string depends on the implementation, but the
 263      * following examples may be regarded as typical:
 264      * <ul>
 265      * <li>
 266      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java:101)}"
 267      * - See the description below.
 268      * </li>
 269      * <li>
 270      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java)}"
 271      * - The line number is unavailable.
 272      * </li>
 273      * <li>
 274      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Unknown Source)}"
 275      * - Neither the file name nor the line number is available.
 276      * </li>
 277      * <li>
 278      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Native Method)}"
 279      * - The method containing the execution point is a native method.
 280      * </li>
 281      * <li>
 282      *     "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}"
 283      * - The class of the execution point is defined in the unnamed module of
 284      * the class loader named {@code com.foo.loader}.
 285      * </li>
 286      * <li>
 287      *     "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}"
 288      * - The class of the execution point is defined in {@code acme} module
 289      * loaded by by a built-in class loader such as the application class loader.
 290      * </li>
 291      * <li>
 292      *     "{@code MyClass.mash(MyClass.java:9)}"
 293      * - {@code MyClass} class is on the application class path.
 294      * </li>
 295      * </ul>
 296      *
 297      * <p> The first example shows a stack trace element consisting of
 298      * three elements, each separated by {@code "/"} followed with
 299      * the source file name and the line number of the source line
 300      * containing the execution point.
 301      *
 302      * The first element "{@code com.foo.loader}" is
 303      * the name of the class loader.  The second element "{@code foo@9.0}"
 304      * is the module name and version.  The third element is the method
 305      * containing the execution point; "{@code com.foo.Main"}" is the
 306      * fully-qualified class name and "{@code run}" is the name of the method.
 307      * "{@code Main.java}" is the source file name and "{@code 101}" is
 308      * the line number.
 309      *
 310      * <p> If a class is defined in an <em>unnamed module</em>
 311      * then the second element is omitted as shown in
 312      * "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}".
 313      *
 314      * <p> If the class loader is a <a href="ClassLoader.html#builtinLoaders">
 315      * built-in class loader</a> or is not named then the first element
 316      * and its following {@code "/"} are omitted as shown in
 317      * "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}".
 318      * If the first element is omitted and the module is an unnamed module,
 319      * the second element and its following {@code "/"} are also omitted
 320      * as shown in "{@code MyClass.mash(MyClass.java:9)}".
 321      *
 322      * <p> Note that different values can be returned from {@link toString()} for
 323      * StackTraceElements that are otherwise {@linkplain #equals(Object) equal}.
 324      * For instance, the class loader name is omitted for built-in class loaders,
 325      * but not for other class loaders.
 326      *
 327      * @see    Throwable#printStackTrace()
 328      */
 329     public String toString() {
 330         String s = "";
 331         if (!has(BUILTIN_CLASS_LOADER) && classLoaderName != null &&
 332                 !classLoaderName.isEmpty()) {
 333             s += classLoaderName + "/";
 334         }
 335         if (moduleName != null && !moduleName.isEmpty()) {
 336             s += moduleName;
 337 
 338             if (!has(JDK_NON_UPGRADEABLE_MODULE) && moduleVersion != null &&
 339                     !moduleVersion.isEmpty()) {
 340                 s += "@" + moduleVersion;
 341             }
 342         }
 343         s = s.isEmpty() ? declaringClass : s + "/" + declaringClass;
 344 
 345         return s + "." + methodName + "(" +
 346              (isNativeMethod() ? "Native Method)" :
 347               (fileName != null && lineNumber >= 0 ?
 348                fileName + ":" + lineNumber + ")" :
 349                 (fileName != null ?  ""+fileName+")" : "Unknown Source)")));
 350     }
 351 
 352     /**
 353      * Returns true if the specified object is another
 354      * {@code StackTraceElement} instance representing the same execution
 355      * point as this instance.  Two stack trace elements {@code a} and
 356      * {@code b} are equal if and only if:
 357      * <pre>{@code
 358      *     equals(a.getClassLoaderName(), b.getClassLoaderName()) &&
 359      *     equals(a.getModuleName(), b.getModuleName()) &&
 360      *     equals(a.getModuleVersion(), b.getModuleVersion()) &&
 361      *     equals(a.getClassName(), b.getClassName()) &&
 362      *     equals(a.getMethodName(), b.getMethodName())
 363      *     equals(a.getFileName(), b.getFileName()) &&
 364      *     a.getLineNumber() == b.getLineNumber()
 365      *
 366      * }</pre>
 367      * where {@code equals} has the semantics of {@link
 368      * java.util.Objects#equals(Object, Object) Objects.equals}.
 369      *
 370      * @apiNote StackTraceElements can be equal, but return different  
 371      * {@link toString()} values, due to the specifics of how the
 372      * {@link toString()} return value is constructed.
 373      * 
 374      * @param  obj the object to be compared with this stack trace element.
 375      * @return true if the specified object is another
 376      *         {@code StackTraceElement} instance representing the same
 377      *         execution point as this instance.
 378      */
 379     public boolean equals(Object obj) {
 380         if (obj==this)
 381             return true;
 382         if (!(obj instanceof StackTraceElement))
 383             return false;
 384         StackTraceElement e = (StackTraceElement)obj;
 385         return Objects.equals(classLoaderName, e.classLoaderName) &&
 386             Objects.equals(moduleName, e.moduleName) &&
 387             Objects.equals(moduleVersion, e.moduleVersion) &&
 388             e.declaringClass.equals(declaringClass) &&
 389             e.lineNumber == lineNumber &&
 390             Objects.equals(methodName, e.methodName) &&
 391             Objects.equals(fileName, e.fileName);
 392     }
 393 
 394     /**
 395      * Returns a hash code value for this stack trace element.
 396      */
 397     public int hashCode() {
 398         int result = 31*declaringClass.hashCode() + methodName.hashCode();
 399         result = 31*result + Objects.hashCode(classLoaderName);
 400         result = 31*result + Objects.hashCode(moduleName);
 401         result = 31*result + Objects.hashCode(moduleVersion);
 402         result = 31*result + Objects.hashCode(fileName);
 403         result = 31*result + lineNumber;
 404         return result;
 405     }
 406 
 407 
 408     /**
 409      * Called from of() methods to set the 'format' bitmap using the Class
 410      * reference stored in declaringClassObject, and then clear the reference.
 411      */
 412     private synchronized void computeFormat() {
 413         try {
 414             Class<?> cls = (Class<?>) declaringClassObject;
 415             ClassLoader loader = cls.getClassLoader0();
 416             Module m = cls.getModule();
 417             byte bits = 0;
 418 
 419             // First element - class loader name
 420             // Call package-private ClassLoader::name method
 421 
 422             if (loader instanceof BuiltinClassLoader) {
 423                 bits |= BUILTIN_CLASS_LOADER;
 424             }
 425 
 426             // Second element - module name and version
 427 
 428             // Omit if is a JDK non-upgradeable module (recorded in the hashes
 429             // in java.base)
 430             if (m != null && m.isNamed() &&
 431                     (isHashedInJavaBase(m) || !m.getDescriptor().version().isPresent())) {
 432                 bits |= JDK_NON_UPGRADEABLE_MODULE;
 433             }
 434             format = bits;
 435         } finally {
 436             // Class reference no longer needed, clear it
 437             declaringClassObject = null;
 438         }
 439     }
 440 
 441     private static final byte BUILTIN_CLASS_LOADER       = 0x1;
 442     private static final byte JDK_NON_UPGRADEABLE_MODULE = 0x2;
 443 
 444     private boolean has(byte bit) {
 445         return (format & bit) == bit;
 446     }
 447 
 448     /**
 449      * Returns true if the module is hashed with java.base.
 450      * <p>
 451      * This method returns false when running on the exploded image
 452      * since JDK modules are not hashed. They have no Version attribute
 453      * and so "@<version>" part will be omitted anyway.
 454      */
 455     private static boolean isHashedInJavaBase(Module m) {
 456         // return true if module system is not initialized as the code
 457         // must be in java.base
 458         if (!VM.isModuleSystemInited())
 459             return true;
 460 
 461         return Layer.boot() == m.getLayer() && HashedModules.contains(m);
 462     }
 463 
 464     /*
 465      * Finds JDK non-upgradeable modules, i.e. the modules that are
 466      * included in the hashes in java.base.
 467      */
 468     private static class HashedModules {
 469         static Set<String> HASHED_MODULES = hashedModules();
 470 
 471         static Set<String> hashedModules() {
 472             Module javaBase = Layer.boot().findModule("java.base").get();
 473             Optional<ModuleHashes> ohashes =
 474                 SharedSecrets.getJavaLangModuleAccess()
 475                              .hashes(javaBase.getDescriptor());
 476 
 477             if (ohashes.isPresent()) {
 478                 Set<String> names = new HashSet<>(ohashes.get().names());
 479                 names.add("java.base");
 480                 return names;
 481             }
 482 
 483             return Set.of();
 484         }
 485 
 486         static boolean contains(Module m) {
 487             return HASHED_MODULES.contains(m.getName());
 488         }
 489     }
 490 
 491 
 492     /*
 493      * Returns an array of StackTraceElements of the given depth
 494      * filled from the backtrace of a given Throwable.
 495      */
 496     static StackTraceElement[] of(Throwable x, int depth) {
 497         StackTraceElement[] stackTrace = new StackTraceElement[depth];
 498         for (int i = 0; i < depth; i++) {
 499             stackTrace[i] = new StackTraceElement();
 500         }
 501 
 502         // VM to fill in StackTraceElement
 503         initStackTraceElements(stackTrace, x);
 504 
 505         // ensure the proper StackTraceElement initialization
 506         for (StackTraceElement ste : stackTrace) {
 507             ste.computeFormat();
 508         }
 509         return stackTrace;
 510     }
 511 
 512     /*
 513      * Returns a StackTraceElement from a given StackFrameInfo.
 514      */
 515     static StackTraceElement of(StackFrameInfo sfi) {
 516         StackTraceElement ste = new StackTraceElement();
 517         initStackTraceElement(ste, sfi);
 518 
 519         ste.computeFormat();
 520         return ste;
 521     }
 522 
 523     /*
 524      * Sets the given stack trace elements with the backtrace
 525      * of the given Throwable.
 526      */
 527     private static native void initStackTraceElements(StackTraceElement[] elements,
 528                                                       Throwable x);
 529     /*
 530      * Sets the given stack trace element with the given StackFrameInfo
 531      */
 532     private static native void initStackTraceElement(StackTraceElement element,
 533                                                      StackFrameInfo sfi);
 534 
 535     private static final long serialVersionUID = 6992337162326171013L;
 536 }