/* * Copyright (c) 1994, 2011, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle in the LICENSE file that accompanied this code. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.lang; import java.io.*; import java.util.*; final class ThrowableHelper { /** * Holder class to defer initializing sentinel objects only used * for serialization. */ private static class SentinelHolder { /** * {@linkplain #setStackTrace(StackTraceElement[]) Setting the * stack trace} to a one-element array containing this sentinel * value indicates future attempts to set the stack trace will be * ignored. The sentinal is equal to the result of calling:
* {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)} */ public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL = new StackTraceElement("", "", null, Integer.MIN_VALUE); /** * Sentinel value used in the serial form to indicate an immutable * stack trace. */ public static final StackTraceElement[] STACK_TRACE_SENTINEL = new StackTraceElement[] {STACK_TRACE_ELEMENT_SENTINEL}; } /** Caption for labeling causative exception stack traces */ private static final String CAUSE_CAPTION = "Caused by: "; /** Caption for labeling suppressed exception stack traces */ private static final String SUPPRESSED_CAPTION = "Suppressed: "; /** * Prints this throwable and its backtrace to the * standard error stream. This method prints a stack trace for this * {@code Throwable} object on the error output stream that is * the value of the field {@code System.err}. The first line of * output contains the result of the {@link #toString()} method for * this object. Remaining lines represent data previously recorded by * the method {@link #fillInStackTrace()}. The format of this * information depends on the implementation, but the following * example may be regarded as typical: *
     * java.lang.NullPointerException
     *         at MyClass.mash(MyClass.java:9)
     *         at MyClass.crunch(MyClass.java:6)
     *         at MyClass.main(MyClass.java:3)
     * 
* This example was produced by running the program: *
     * class MyClass {
     *     public static void main(String[] args) {
     *         crunch(null);
     *     }
     *     static void crunch(int[] a) {
     *         mash(a);
     *     }
     *     static void mash(int[] b) {
     *         System.out.println(b[0]);
     *     }
     * }
     * 
* The backtrace for a throwable with an initialized, non-null cause * should generally include the backtrace for the cause. The format * of this information depends on the implementation, but the following * example may be regarded as typical: *
     * HighLevelException: MidLevelException: LowLevelException
     *         at Junk.a(Junk.java:13)
     *         at Junk.main(Junk.java:4)
     * Caused by: MidLevelException: LowLevelException
     *         at Junk.c(Junk.java:23)
     *         at Junk.b(Junk.java:17)
     *         at Junk.a(Junk.java:11)
     *         ... 1 more
     * Caused by: LowLevelException
     *         at Junk.e(Junk.java:30)
     *         at Junk.d(Junk.java:27)
     *         at Junk.c(Junk.java:21)
     *         ... 3 more
     * 
* Note the presence of lines containing the characters {@code "..."}. * These lines indicate that the remainder of the stack trace for this * exception matches the indicated number of frames from the bottom of the * stack trace of the exception that was caused by this exception (the * "enclosing" exception). This shorthand can greatly reduce the length * of the output in the common case where a wrapped exception is thrown * from same method as the "causative exception" is caught. The above * example was produced by running the program: *
     * public class Junk {
     *     public static void main(String args[]) {
     *         try {
     *             a();
     *         } catch(HighLevelException e) {
     *             e.printStackTrace();
     *         }
     *     }
     *     static void a() throws HighLevelException {
     *         try {
     *             b();
     *         } catch(MidLevelException e) {
     *             throw new HighLevelException(e);
     *         }
     *     }
     *     static void b() throws MidLevelException {
     *         c();
     *     }
     *     static void c() throws MidLevelException {
     *         try {
     *             d();
     *         } catch(LowLevelException e) {
     *             throw new MidLevelException(e);
     *         }
     *     }
     *     static void d() throws LowLevelException {
     *        e();
     *     }
     *     static void e() throws LowLevelException {
     *         throw new LowLevelException();
     *     }
     * }
     *
     * class HighLevelException extends Exception {
     *     HighLevelException(Throwable cause) { super(cause); }
     * }
     *
     * class MidLevelException extends Exception {
     *     MidLevelException(Throwable cause)  { super(cause); }
     * }
     *
     * class LowLevelException extends Exception {
     * }
     * 
* As of release 7, the platform supports the notion of * suppressed exceptions (in conjunction with the {@code * try}-with-resources statement). Any exceptions that were * suppressed in order to deliver an exception are printed out * beneath the stack trace. The format of this information * depends on the implementation, but the following example may be * regarded as typical: * *
     * Exception in thread "main" java.lang.Exception: Something happened
     *  at Foo.bar(Foo.java:10)
     *  at Foo.main(Foo.java:5)
     *  Suppressed: Resource$CloseFailException: Resource ID = 0
     *          at Resource.close(Resource.java:26)
     *          at Foo.bar(Foo.java:9)
     *          ... 1 more
     * 
* Note that the "... n more" notation is used on suppressed exceptions * just at it is used on causes. Unlike causes, suppressed exceptions are * indented beyond their "containing exceptions." * *

An exception can have both a cause and one or more suppressed * exceptions: *

     * Exception in thread "main" java.lang.Exception: Main block
     *  at Foo3.main(Foo3.java:7)
     *  Suppressed: Resource$CloseFailException: Resource ID = 2
     *          at Resource.close(Resource.java:26)
     *          at Foo3.main(Foo3.java:5)
     *  Suppressed: Resource$CloseFailException: Resource ID = 1
     *          at Resource.close(Resource.java:26)
     *          at Foo3.main(Foo3.java:5)
     * Caused by: java.lang.Exception: I did it
     *  at Foo3.main(Foo3.java:8)
     * 
* Likewise, a suppressed exception can have a cause: *
     * Exception in thread "main" java.lang.Exception: Main block
     *  at Foo4.main(Foo4.java:6)
     *  Suppressed: Resource2$CloseFailException: Resource ID = 1
     *          at Resource2.close(Resource2.java:20)
     *          at Foo4.main(Foo4.java:5)
     *  Caused by: java.lang.Exception: Rats, you caught me
     *          at Resource2$CloseFailException.(Resource2.java:45)
     *          ... 2 more
     * 
*/ public static void printStackTrace(Throwable _this) { _this.printStackTrace(System.err); } /** * Prints this throwable and its backtrace to the specified print stream. * * @param s {@code PrintStream} to use for output */ public static void printStackTrace(Throwable _this, PrintStream s) { printStackTrace(_this, new WrappedPrintStream(s)); } private static void printStackTrace(Throwable _this, PrintStreamOrWriter s) { // Guard against malicious overrides of Throwable.equals by // using a Set with identity equality semantics. Set dejaVu = Collections.newSetFromMap(new IdentityHashMap()); dejaVu.add(_this); synchronized (s.lock()) { // Print our stack trace s.println(_this); StackTraceElement[] trace = getOurStackTrace(_this); for (StackTraceElement traceElement : trace) s.println("\tat " + traceElement); // Print suppressed exceptions, if any for (Throwable se : _this.getSuppressed()) printEnclosedStackTrace(se, s, trace, SUPPRESSED_CAPTION, "\t", dejaVu); // Print cause, if any Throwable ourCause = _this.getCause(); if (ourCause != null) printEnclosedStackTrace(ourCause, s, trace, CAUSE_CAPTION, "", dejaVu); } } /** * Print our stack trace as an enclosed exception for the specified * stack trace. */ private static void printEnclosedStackTrace(Throwable _this, PrintStreamOrWriter s, StackTraceElement[] enclosingTrace, String caption, String prefix, Set dejaVu) { assert Thread.holdsLock(s.lock()); if (dejaVu.contains(_this)) { s.println("\t[CIRCULAR REFERENCE:" + _this + "]"); } else { dejaVu.add(_this); // Compute number of frames in common between this and enclosing trace StackTraceElement[] trace = getOurStackTrace(_this); int m = trace.length - 1; int n = enclosingTrace.length - 1; while (m >= 0 && n >=0 && trace[m].equals(enclosingTrace[n])) { m--; n--; } int framesInCommon = trace.length - 1 - m; // Print our stack trace s.println(prefix + caption + _this); for (int i = 0; i <= m; i++) s.println(prefix + "\tat " + trace[i]); if (framesInCommon != 0) s.println(prefix + "\t... " + framesInCommon + " more"); // Print suppressed exceptions, if any for (Throwable se : _this.getSuppressed()) printEnclosedStackTrace(se, s, trace, SUPPRESSED_CAPTION, prefix +"\t", dejaVu); // Print cause, if any Throwable ourCause = _this.getCause(); if (ourCause != null) printEnclosedStackTrace(ourCause, s, trace, CAUSE_CAPTION, prefix, dejaVu); } } private static native StackTraceElement[] getOurStackTrace(Throwable _this); /** * Prints this throwable and its backtrace to the specified * print writer. * * @param s {@code PrintWriter} to use for output * @since JDK1.1 */ public static void printStackTrace(Throwable _this, PrintWriter s) { printStackTrace(_this, new WrappedPrintWriter(s)); } /** * Wrapper class for PrintStream and PrintWriter to enable a single * implementation of printStackTrace. */ private abstract static class PrintStreamOrWriter { /** Returns the object to be locked when using this StreamOrWriter */ abstract Object lock(); /** Prints the specified string as a line on this StreamOrWriter */ abstract void println(Object o); } private static class WrappedPrintStream extends PrintStreamOrWriter { private final PrintStream printStream; WrappedPrintStream(PrintStream printStream) { this.printStream = printStream; } Object lock() { return printStream; } void println(Object o) { printStream.println(o); } } private static class WrappedPrintWriter extends PrintStreamOrWriter { private final PrintWriter printWriter; WrappedPrintWriter(PrintWriter printWriter) { this.printWriter = printWriter; } Object lock() { return printWriter; } void println(Object o) { printWriter.println(o); } } }