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.VM;
  30 import jdk.internal.module.ModuleHashes;
  31 import jdk.internal.module.ModuleReferenceImpl;
  32 
  33 import java.lang.module.ModuleDescriptor.Version;
  34 import java.lang.module.ModuleReference;
  35 import java.lang.module.ResolvedModule;
  36 import java.util.HashSet;
  37 import java.util.Objects;
  38 import java.util.Optional;
  39 import java.util.Set;
  40 
  41 /**
  42  * An element in a stack trace, as returned by {@link
  43  * Throwable#getStackTrace()}.  Each element represents a single stack frame.
  44  * All stack frames except for the one at the top of the stack represent
  45  * a method invocation.  The frame at the top of the stack represents the
  46  * execution point at which the stack trace was generated.  Typically,
  47  * this is the point at which the throwable corresponding to the stack trace
  48  * was created.
  49  *
  50  * @since  1.4
  51  * @author Josh Bloch
  52  */
  53 public final class StackTraceElement implements java.io.Serializable {
  54 
  55     // For Throwables and StackWalker, the VM initially sets this field to a
  56     // reference to the declaring Class.  The Class reference is used to
  57     // construct the 'format' bitmap, and then is cleared.
  58     //
  59     // For STEs constructed using the public constructors, this field is not used.
  60     private transient Class<?> declaringClassObject;
  61 
  62     // Normally initialized by VM
  63     private String classLoaderName;
  64     private String moduleName;
  65     private String moduleVersion;
  66     private String declaringClass;
  67     private String methodName;
  68     private String fileName;
  69     private int    lineNumber;
  70     private byte   format = 0; // Default to show all
  71 
  72     /**
  73      * Creates a stack trace element representing the specified execution
  74      * point. The {@link #getModuleName module name} and {@link
  75      * #getModuleVersion module version} of the stack trace element will
  76      * be {@code null}.
  77      *
  78      * @param declaringClass the fully qualified name of the class containing
  79      *        the execution point represented by the stack trace element
  80      * @param methodName the name of the method containing the execution point
  81      *        represented by the stack trace element
  82      * @param fileName the name of the file containing the execution point
  83      *         represented by the stack trace element, or {@code null} if
  84      *         this information is unavailable
  85      * @param lineNumber the line number of the source line containing the
  86      *         execution point represented by this stack trace element, or
  87      *         a negative number if this information is unavailable. A value
  88      *         of -2 indicates that the method containing the execution point
  89      *         is a native method
  90      * @throws NullPointerException if {@code declaringClass} or
  91      *         {@code methodName} is null
  92      * @since 1.5
  93      * @revised 9
  94      * @spec JPMS
  95      */
  96     public StackTraceElement(String declaringClass, String methodName,
  97                              String fileName, int lineNumber) {
  98         this(null, null, null, declaringClass, methodName, fileName, lineNumber);
  99     }
 100 
 101     /**
 102      * Creates a stack trace element representing the specified execution
 103      * point.
 104      *
 105      * @param classLoaderName the class loader name if the class loader of
 106      *        the class containing the execution point represented by
 107      *        the stack trace is named; otherwise {@code null}
 108      * @param moduleName the module name if the class containing the
 109      *        execution point represented by the stack trace is in a named
 110      *        module; otherwise {@code null}
 111      * @param moduleVersion the module version if the class containing the
 112      *        execution point represented by the stack trace is in a named
 113      *        module that has a version; otherwise {@code null}
 114      * @param declaringClass the fully qualified name of the class containing
 115      *        the execution point represented by the stack trace element
 116      * @param methodName the name of the method containing the execution point
 117      *        represented by the stack trace element
 118      * @param fileName the name of the file containing the execution point
 119      *        represented by the stack trace element, or {@code null} if
 120      *        this information is unavailable
 121      * @param lineNumber the line number of the source line containing the
 122      *        execution point represented by this stack trace element, or
 123      *        a negative number if this information is unavailable. A value
 124      *        of -2 indicates that the method containing the execution point
 125      *        is a native method
 126      *
 127      * @throws NullPointerException if {@code declaringClass} is {@code null}
 128      *         or {@code methodName} is {@code null}
 129      *
 130      * @since 9
 131      * @spec JPMS
 132      */
 133     public StackTraceElement(String classLoaderName,
 134                              String moduleName, String moduleVersion,
 135                              String declaringClass, String methodName,
 136                              String fileName, int lineNumber) {
 137         this.classLoaderName = classLoaderName;
 138         this.moduleName      = moduleName;
 139         this.moduleVersion   = moduleVersion;
 140         this.declaringClass  = Objects.requireNonNull(declaringClass, "Declaring class is null");
 141         this.methodName      = Objects.requireNonNull(methodName, "Method name is null");
 142         this.fileName        = fileName;
 143         this.lineNumber      = lineNumber;
 144     }
 145 
 146     /*
 147      * Private constructor for the factory methods to create StackTraceElement
 148      * for Throwable and StackFrameInfo
 149      */
 150     private StackTraceElement() {}
 151 
 152     /**
 153      * Returns the name of the source file containing the execution point
 154      * represented by this stack trace element.  Generally, this corresponds
 155      * to the {@code SourceFile} attribute of the relevant {@code class}
 156      * file (as per <i>The Java Virtual Machine Specification</i>, Section
 157      * 4.7.7).  In some systems, the name may refer to some source code unit
 158      * other than a file, such as an entry in source repository.
 159      *
 160      * @return the name of the file containing the execution point
 161      *         represented by this stack trace element, or {@code null} if
 162      *         this information is unavailable.
 163      */
 164     public String getFileName() {
 165         return fileName;
 166     }
 167 
 168     /**
 169      * Returns the line number of the source line containing the execution
 170      * point represented by this stack trace element.  Generally, this is
 171      * derived from the {@code LineNumberTable} attribute of the relevant
 172      * {@code class} file (as per <i>The Java Virtual Machine
 173      * Specification</i>, Section 4.7.8).
 174      *
 175      * @return the line number of the source line containing the execution
 176      *         point represented by this stack trace element, or a negative
 177      *         number if this information is unavailable.
 178      */
 179     public int getLineNumber() {
 180         return lineNumber;
 181     }
 182 
 183     /**
 184      * Returns the module name of the module containing the execution point
 185      * represented by this stack trace element.
 186      *
 187      * @return the module name of the {@code Module} containing the execution
 188      *         point represented by this stack trace element; {@code null}
 189      *         if the module name is not available.
 190      * @since 9
 191      * @spec JPMS
 192      * @see Module#getName()
 193      */
 194     public String getModuleName() {
 195         return moduleName;
 196     }
 197 
 198     /**
 199      * Returns the module version of the module containing the execution point
 200      * represented by this stack trace element.
 201      *
 202      * @return the module version of the {@code Module} containing the execution
 203      *         point represented by this stack trace element; {@code null}
 204      *         if the module version is not available.
 205      * @since 9
 206      * @spec JPMS
 207      * @see java.lang.module.ModuleDescriptor.Version
 208      */
 209     public String getModuleVersion() {
 210         return moduleVersion;
 211     }
 212 
 213     /**
 214      * Returns the name of the class loader of the class containing the
 215      * execution point represented by this stack trace element.
 216      *
 217      * @return the name of the class loader of the class containing the execution
 218      *         point represented by this stack trace element; {@code null}
 219      *         if the class loader is not named.
 220      *
 221      * @since 9
 222      * @spec JPMS
 223      * @see java.lang.ClassLoader#getName()
 224      */
 225     public String getClassLoaderName() {
 226         return classLoaderName;
 227     }
 228 
 229     /**
 230      * Returns the fully qualified name of the class containing the
 231      * execution point represented by this stack trace element.
 232      *
 233      * @return the fully qualified name of the {@code Class} containing
 234      *         the execution point represented by this stack trace element.
 235      */
 236     public String getClassName() {
 237         return declaringClass;
 238     }
 239 
 240     /**
 241      * Returns the name of the method containing the execution point
 242      * represented by this stack trace element.  If the execution point is
 243      * contained in an instance or class initializer, this method will return
 244      * the appropriate <i>special method name</i>, {@code <init>} or
 245      * {@code <clinit>}, as per Section 3.9 of <i>The Java Virtual
 246      * Machine Specification</i>.
 247      *
 248      * @return the name of the method containing the execution point
 249      *         represented by this stack trace element.
 250      */
 251     public String getMethodName() {
 252         return methodName;
 253     }
 254 
 255     /**
 256      * Returns true if the method containing the execution point
 257      * represented by this stack trace element is a native method.
 258      *
 259      * @return {@code true} if the method containing the execution point
 260      *         represented by this stack trace element is a native method.
 261      */
 262     public boolean isNativeMethod() {
 263         return lineNumber == -2;
 264     }
 265 
 266     /**
 267      * Returns a string representation of this stack trace element.
 268      *
 269      * @apiNote The format of this string depends on the implementation, but the
 270      * following examples may be regarded as typical:
 271      * <ul>
 272      * <li>
 273      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java:101)}"
 274      * - See the description below.
 275      * </li>
 276      * <li>
 277      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Main.java)}"
 278      * - The line number is unavailable.
 279      * </li>
 280      * <li>
 281      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Unknown Source)}"
 282      * - Neither the file name nor the line number is available.
 283      * </li>
 284      * <li>
 285      *     "{@code com.foo.loader/foo@9.0/com.foo.Main.run(Native Method)}"
 286      * - The method containing the execution point is a native method.
 287      * </li>
 288      * <li>
 289      *     "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}"
 290      * - The class of the execution point is defined in the unnamed module of
 291      * the class loader named {@code com.foo.loader}.
 292      * </li>
 293      * <li>
 294      *     "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}"
 295      * - The class of the execution point is defined in {@code acme} module
 296      * loaded by a built-in class loader such as the application class loader.
 297      * </li>
 298      * <li>
 299      *     "{@code MyClass.mash(MyClass.java:9)}"
 300      * - {@code MyClass} class is on the application class path.
 301      * </li>
 302      * </ul>
 303      *
 304      * <p> The first example shows a stack trace element consisting of
 305      * three elements, each separated by {@code "/"} followed with
 306      * the source file name and the line number of the source line
 307      * containing the execution point.
 308      *
 309      * The first element "{@code com.foo.loader}" is
 310      * the name of the class loader.  The second element "{@code foo@9.0}"
 311      * is the module name and version.  The third element is the method
 312      * containing the execution point; "{@code com.foo.Main"}" is the
 313      * fully-qualified class name and "{@code run}" is the name of the method.
 314      * "{@code Main.java}" is the source file name and "{@code 101}" is
 315      * the line number.
 316      *
 317      * <p> If a class is defined in an <em>unnamed module</em>
 318      * then the second element is omitted as shown in
 319      * "{@code com.foo.loader//com.foo.bar.App.run(App.java:12)}".
 320      *
 321      * <p> If the class loader is a <a href="ClassLoader.html#builtinLoaders">
 322      * built-in class loader</a> or is not named then the first element
 323      * and its following {@code "/"} are omitted as shown in
 324      * "{@code acme@2.1/org.acme.Lib.test(Lib.java:80)}".
 325      * If the first element is omitted and the module is an unnamed module,
 326      * the second element and its following {@code "/"} are also omitted
 327      * as shown in "{@code MyClass.mash(MyClass.java:9)}".
 328      *
 329      * <p> The {@code toString} method may return two different values on two
 330      * {@code StackTraceElement} instances that are
 331      * {@linkplain #equals(Object) equal}, for example one created via the
 332      * constructor, and one obtained from {@link java.lang.Throwable} or
 333      * {@link java.lang.StackWalker.StackFrame}, where an implementation may
 334      * choose to omit some element in the returned string.
 335      *
 336      * @revised 9
 337      * @spec JPMS
 338      * @see    Throwable#printStackTrace()
 339      */
 340     public String toString() {
 341         String s = "";
 342         if (!dropClassLoaderName() && classLoaderName != null &&
 343                 !classLoaderName.isEmpty()) {
 344             s += classLoaderName + "/";
 345         }
 346         if (moduleName != null && !moduleName.isEmpty()) {
 347             s += moduleName;
 348 
 349             if (!dropModuleVersion() && moduleVersion != null &&
 350                     !moduleVersion.isEmpty()) {
 351                 s += "@" + moduleVersion;
 352             }
 353         }
 354         s = s.isEmpty() ? declaringClass : s + "/" + declaringClass;
 355 
 356         return s + "." + methodName + "(" +
 357              (isNativeMethod() ? "Native Method)" :
 358               (fileName != null && lineNumber >= 0 ?
 359                fileName + ":" + lineNumber + ")" :
 360                 (fileName != null ?  ""+fileName+")" : "Unknown Source)")));
 361     }
 362 
 363     /**
 364      * Returns true if the specified object is another
 365      * {@code StackTraceElement} instance representing the same execution
 366      * point as this instance.  Two stack trace elements {@code a} and
 367      * {@code b} are equal if and only if:
 368      * <pre>{@code
 369      *     equals(a.getClassLoaderName(), b.getClassLoaderName()) &&
 370      *     equals(a.getModuleName(), b.getModuleName()) &&
 371      *     equals(a.getModuleVersion(), b.getModuleVersion()) &&
 372      *     equals(a.getClassName(), b.getClassName()) &&
 373      *     equals(a.getMethodName(), b.getMethodName())
 374      *     equals(a.getFileName(), b.getFileName()) &&
 375      *     a.getLineNumber() == b.getLineNumber()
 376      *
 377      * }</pre>
 378      * where {@code equals} has the semantics of {@link
 379      * java.util.Objects#equals(Object, Object) Objects.equals}.
 380      *
 381      * @param  obj the object to be compared with this stack trace element.
 382      * @return true if the specified object is another
 383      *         {@code StackTraceElement} instance representing the same
 384      *         execution point as this instance.
 385      *
 386      * @revised 9
 387      * @spec JPMS
 388      */
 389     public boolean equals(Object obj) {
 390         if (obj==this)
 391             return true;
 392         if (!(obj instanceof StackTraceElement))
 393             return false;
 394         StackTraceElement e = (StackTraceElement)obj;
 395         return Objects.equals(classLoaderName, e.classLoaderName) &&
 396             Objects.equals(moduleName, e.moduleName) &&
 397             Objects.equals(moduleVersion, e.moduleVersion) &&
 398             e.declaringClass.equals(declaringClass) &&
 399             e.lineNumber == lineNumber &&
 400             Objects.equals(methodName, e.methodName) &&
 401             Objects.equals(fileName, e.fileName);
 402     }
 403 
 404     /**
 405      * Returns a hash code value for this stack trace element.
 406      */
 407     public int hashCode() {
 408         int result = 31*declaringClass.hashCode() + methodName.hashCode();
 409         result = 31*result + Objects.hashCode(classLoaderName);
 410         result = 31*result + Objects.hashCode(moduleName);
 411         result = 31*result + Objects.hashCode(moduleVersion);
 412         result = 31*result + Objects.hashCode(fileName);
 413         result = 31*result + lineNumber;
 414         return result;
 415     }
 416 
 417 
 418     /**
 419      * Called from of() methods to set the 'format' bitmap using the Class
 420      * reference stored in declaringClassObject, and then clear the reference.
 421      *
 422      * <p>
 423      * If the module is a non-upgradeable JDK module, then set
 424      * JDK_NON_UPGRADEABLE_MODULE to omit its version string.
 425      * <p>
 426      * If the loader is one of the built-in loaders (`boot`, `platform`, or `app`)
 427      * then set BUILTIN_CLASS_LOADER to omit the first element (`<loader>/`).
 428      */
 429     private synchronized void computeFormat() {
 430         try {
 431             Class<?> cls = (Class<?>) declaringClassObject;
 432             ClassLoader loader = cls.getClassLoader0();
 433             Module m = cls.getModule();
 434             byte bits = 0;
 435 
 436             // First element - class loader name
 437             // Call package-private ClassLoader::name method
 438 
 439             if (loader instanceof BuiltinClassLoader) {
 440                 bits |= BUILTIN_CLASS_LOADER;
 441             }
 442 
 443             // Second element - module name and version
 444 
 445             // Omit if is a JDK non-upgradeable module (recorded in the hashes
 446             // in java.base)
 447             if (isHashedInJavaBase(m)) {
 448                 bits |= JDK_NON_UPGRADEABLE_MODULE;
 449             }
 450             format = bits;
 451         } finally {
 452             // Class reference no longer needed, clear it
 453             declaringClassObject = null;
 454         }
 455     }
 456 
 457     private static final byte BUILTIN_CLASS_LOADER       = 0x1;
 458     private static final byte JDK_NON_UPGRADEABLE_MODULE = 0x2;
 459 
 460     private boolean dropClassLoaderName() {
 461         return (format & BUILTIN_CLASS_LOADER) == BUILTIN_CLASS_LOADER;
 462     }
 463 
 464     private boolean dropModuleVersion() {
 465         return (format & JDK_NON_UPGRADEABLE_MODULE) == JDK_NON_UPGRADEABLE_MODULE;
 466     }
 467 
 468     /**
 469      * Returns true if the module is hashed with java.base.
 470      * <p>
 471      * This method returns false when running on the exploded image
 472      * since JDK modules are not hashed. They have no Version attribute
 473      * and so "@<version>" part will be omitted anyway.
 474      */
 475     private static boolean isHashedInJavaBase(Module m) {
 476         // return true if module system is not initialized as the code
 477         // must be in java.base
 478         if (!VM.isModuleSystemInited())
 479             return true;
 480 
 481         return ModuleLayer.boot() == m.getLayer() && HashedModules.contains(m);
 482     }
 483 
 484     /*
 485      * Finds JDK non-upgradeable modules, i.e. the modules that are
 486      * included in the hashes in java.base.
 487      */
 488     private static class HashedModules {
 489         static Set<String> HASHED_MODULES = hashedModules();
 490 
 491         static Set<String> hashedModules() {
 492 
 493             Optional<ResolvedModule> resolvedModule = ModuleLayer.boot()
 494                     .configuration()
 495                     .findModule("java.base");
 496             assert resolvedModule.isPresent();
 497             ModuleReference mref = resolvedModule.get().reference();
 498             assert mref instanceof ModuleReferenceImpl;
 499             ModuleHashes hashes = ((ModuleReferenceImpl)mref).recordedHashes();
 500             if (hashes != null) {
 501                 Set<String> names = new HashSet<>(hashes.names());
 502                 names.add("java.base");
 503                 return names;
 504             }
 505 
 506             return Set.of();
 507         }
 508 
 509         static boolean contains(Module m) {
 510             return HASHED_MODULES.contains(m.getName());
 511         }
 512     }
 513 
 514 
 515     /*
 516      * Returns an array of StackTraceElements of the given depth
 517      * filled from the backtrace of a given Throwable.
 518      */
 519     static StackTraceElement[] of(Throwable x, int depth) {
 520         StackTraceElement[] stackTrace = new StackTraceElement[depth];
 521         for (int i = 0; i < depth; i++) {
 522             stackTrace[i] = new StackTraceElement();
 523         }
 524 
 525         // VM to fill in StackTraceElement
 526         initStackTraceElements(stackTrace, x);
 527 
 528         // ensure the proper StackTraceElement initialization
 529         for (StackTraceElement ste : stackTrace) {
 530             ste.computeFormat();
 531         }
 532         return stackTrace;
 533     }
 534 
 535     /*
 536      * Returns a StackTraceElement from a given StackFrameInfo.
 537      */
 538     static StackTraceElement of(StackFrameInfo sfi) {
 539         StackTraceElement ste = new StackTraceElement();
 540         initStackTraceElement(ste, sfi);
 541 
 542         ste.computeFormat();
 543         return ste;
 544     }
 545 
 546     /*
 547      * Sets the given stack trace elements with the backtrace
 548      * of the given Throwable.
 549      */
 550     private static native void initStackTraceElements(StackTraceElement[] elements,
 551                                                       Throwable x);
 552     /*
 553      * Sets the given stack trace element with the given StackFrameInfo
 554      */
 555     private static native void initStackTraceElement(StackTraceElement element,
 556                                                      StackFrameInfo sfi);
 557 
 558     @java.io.Serial
 559     private static final long serialVersionUID = 6992337162326171013L;
 560 }