/*
* 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.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.Collections;
import java.util.IdentityHashMap;
import java.util.List;
import java.util.Set;
/**
* The {@code Throwable} class is the superclass of all errors and exceptions in
* the Java language. Only objects that are instances of this class (or one of
* its subclasses) are thrown by the Java Virtual Machine or can be thrown by
* the Java {@code throw} statement. Similarly, only this class or one of its
* subclasses can be the argument type in a {@code catch} clause.
*
* For the purposes of compile-time checking of exceptions, {@code Throwable}
* and any subclass of {@code Throwable} that is not also a subclass of either
* {@link RuntimeException} or {@link Error} are regarded as checked exceptions.
*
* <p>
* Instances of two subclasses, {@link java.lang.Error} and
* {@link java.lang.Exception}, are conventionally used to indicate that
* exceptional situations have occurred. Typically, these instances are freshly
* created in the context of the exceptional situation so as to include relevant
* information (such as stack trace data).
*
* <p>
* A throwable contains a snapshot of the execution stack of its thread at the
* time it was created. It can also contain a message string that gives more
* information about the error. Over time, a throwable can
* {@linkplain Throwable#addSuppressed suppress} other throwables from being
* propagated. Finally, the throwable can also contain a <i>cause</i>: another
* throwable that caused this throwable to be constructed. The recording of this
* causal information is referred to as the <i>chained exception</i> facility,
* as the cause can, itself, have a cause, and so on, leading to a "chain" of
* exceptions, each caused by another.
*
* <p>
* One reason that a throwable may have a cause is that the class that throws it
* is built atop a lower layered abstraction, and an operation on the upper
* layer fails due to a failure in the lower layer. It would be bad design to
* let the throwable thrown by the lower layer propagate outward, as it is
* generally unrelated to the abstraction provided by the upper layer. Further,
* doing so would tie the API of the upper layer to the details of its
* implementation, assuming the lower layer's exception was a checked exception.
* Throwing a "wrapped exception" (i.e., an exception containing a cause) allows
* the upper layer to communicate the details of the failure to its caller
* without incurring either of these shortcomings. It preserves the flexibility
* to change the implementation of the upper layer without changing its API (in
* particular, the set of exceptions thrown by its methods).
*
* <p>
* A second reason that a throwable may have a cause is that the method that
* throws it must conform to a general-purpose interface that does not permit
* the method to throw the cause directly. For example, suppose a persistent
* collection conforms to the {@link java.util.Collection Collection} interface,
* and that its persistence is implemented atop {@code java.io}. Suppose the
* internals of the {@code add} method can throw an {@link java.io.IOException
* IOException}. The implementation can communicate the details of the
* {@code IOException} to its caller while conforming to the {@code Collection}
* interface by wrapping the {@code IOException} in an appropriate unchecked
* exception. (The specification for the persistent collection should indicate
* that it is capable of throwing such exceptions.)
*
* <p>
* A cause can be associated with a throwable in two ways: via a constructor
* that takes the cause as an argument, or via the {@link #initCause(Throwable)}
* method. New throwable classes that wish to allow causes to be associated with
* them should provide constructors that take a cause and delegate (perhaps
* indirectly) to one of the {@code Throwable} constructors that takes a cause.
*
* Because the {@code initCause} method is public, it allows a cause to be
* associated with any throwable, even a "legacy throwable" whose implementation
* predates the addition of the exception chaining mechanism to
* {@code Throwable}.
*
* <p>
* By convention, class {@code Throwable} and its subclasses have two
* constructors, one that takes no arguments and one that takes a {@code String}
* argument that can be used to produce a detail message. Further, those
* subclasses that might likely have a cause associated with them should have
* two more constructors, one that takes a {@code Throwable} (the cause), and
* one that takes a {@code String} (the detail message) and a {@code Throwable}
* (the cause).
*
* @author unascribed
* @author Josh Bloch (Added exception chaining and programmatic access to stack
* trace in 1.4.)
* @jls 11.2 Compile-Time Checking of Exceptions
* @since JDK1.0
*/
public class Throwable implements Serializable {
/** use serialVersionUID from JDK 1.0.2 for interoperability */
private static final long serialVersionUID = -3042686055658047285L;
/**
* Native code saves some indication of the stack backtrace in this slot.
*/
private transient Object backtrace;
/**
* Specific details about the Throwable. For example, for
* {@code FileNotFoundException}, this contains the name of the file that
* could not be found.
*
* @serial
*/
private String detailMessage;
/**
* 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:<br>
* {@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 };
}
/**
* A shared value for an empty stack.
*/
private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];
/*
* To allow Throwable objects to be made immutable and safely reused by the
* JVM, such as OutOfMemoryErrors, fields of Throwable that are writable in
* response to user actions, cause, stackTrace, and suppressedExceptions
* obey the following protocol:
*
* 1) The fields are initialized to a non-null sentinel value which
* indicates the value has logically not been set.
*
* 2) Writing a null to the field indicates further writes are forbidden
*
* 3) The sentinel value may be replaced with another non-null value.
*
* For example, implementations of the HotSpot JVM have preallocated
* OutOfMemoryError objects to provide for better diagnosability of that
* situation. These objects are created without calling the constructor for
* that class and the fields in question are initialized to null. To support
* this capability, any new fields added to Throwable that require being
* initialized to a non-null value require a coordinated JVM change.
*/
/**
* The throwable that caused this throwable to get thrown, or null if this
* throwable was not caused by another throwable, or if the causative
* throwable is unknown. If this field is equal to this throwable itself, it
* indicates that the cause of this throwable has not yet been initialized.
*
* @serial
* @since 1.4
*/
private Throwable cause = this;
/**
* The stack trace, as returned by {@link #getStackTrace()}.
*
* The field is initialized to a zero-length array. A {@code null} value of
* this field indicates subsequent calls to
* {@link #setStackTrace(StackTraceElement[])} and
* {@link #fillInStackTrace()} will be be no-ops.
*
* @serial
* @since 1.4
*/
private StackTraceElement[] stackTrace = UNASSIGNED_STACK;
// Setting this static field introduces an acceptable
// initialization dependency on a few java.util classes.
private static final List<Throwable> SUPPRESSED_SENTINEL = Collections
.unmodifiableList(new ArrayList<Throwable>(0));
/**
* The list of suppressed exceptions, as returned by
* {@link #getSuppressed()}. The list is initialized to a zero-element
* unmodifiable sentinel list. When a serialized Throwable is read in, if
* the {@code suppressedExceptions} field points to a zero-element list, the
* field is reset to the sentinel value.
*
* @serial
* @since 1.7
*/
private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;
/** Message for trying to suppress a null exception. */
private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";
/** Message for trying to suppress oneself. */
private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";
/** 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: ";
/**
* Constructs a new throwable with {@code null} as its detail message. The
* cause is not initialized, and may subsequently be initialized by a call
* to {@link #initCause}.
*
* <p>
* The {@link #fillInStackTrace()} method is called to initialize the stack
* trace data in the newly created throwable.
*/
public Throwable() {
fillInStackTrace();
}
/**
* Constructs a new throwable with the specified detail message. The cause
* is not initialized, and may subsequently be initialized by a call to
* {@link #initCause}.
*
* <p>
* The {@link #fillInStackTrace()} method is called to initialize the stack
* trace data in the newly created throwable.
*
* @param message
* the detail message. The detail message is saved for later
* retrieval by the {@link #getMessage()} method.
*/
public Throwable(String message) {
fillInStackTrace();
detailMessage = message;
}
/**
* Constructs a new throwable with the specified detail message and cause.
* <p>
* Note that the detail message associated with {@code cause} is <i>not</i>
* automatically incorporated in this throwable's detail message.
*
* <p>
* The {@link #fillInStackTrace()} method is called to initialize the stack
* trace data in the newly created throwable.
*
* @param message
* the detail message (which is saved for later retrieval by the
* {@link #getMessage()} method).
* @param cause
* the cause (which is saved for later retrieval by the
* {@link #getCause()} method). (A {@code null} value is
* permitted, and indicates that the cause is nonexistent or
* unknown.)
* @since 1.4
*/
public Throwable(String message, Throwable cause) {
fillInStackTrace();
detailMessage = message;
this.cause = cause;
}
/**
* Constructs a new throwable with the specified cause and a detail message
* of {@code (cause==null ? null : cause.toString())} (which typically
* contains the class and detail message of {@code cause}). This constructor
* is useful for throwables that are little more than wrappers for other
* throwables (for example, {@link java.security.PrivilegedActionException}
* ).
*
* <p>
* The {@link #fillInStackTrace()} method is called to initialize the stack
* trace data in the newly created throwable.
*
* @param cause
* the cause (which is saved for later retrieval by the
* {@link #getCause()} method). (A {@code null} value is
* permitted, and indicates that the cause is nonexistent or
* unknown.)
* @since 1.4
*/
public Throwable(Throwable cause) {
fillInStackTrace();
detailMessage = (cause == null ? null : cause.toString());
this.cause = cause;
}
/**
* Constructs a new throwable with the specified detail message, cause,
* {@linkplain #addSuppressed suppression} enabled or disabled, and writable
* stack trace enabled or disabled. If suppression is disabled,
* {@link #getSuppressed} for this object will return a zero-length array
* and calls to {@link #addSuppressed} that would otherwise append an
* exception to the suppressed list will have no effect. If the writable
* stack trace is false, this constructor will not call
* {@link #fillInStackTrace()}, a {@code null} will be written to the
* {@code stackTrace} field, and subsequent calls to
* {@code fillInStackTrace} and {@link #setStackTrace(StackTraceElement[])}
* will not set the stack trace. If the writable stack trace is false,
* {@link #getStackTrace} will return a zero length array.
*
* <p>
* Note that the other constructors of {@code Throwable} treat suppression
* as being enabled and the stack trace as being writable. Subclasses of
* {@code Throwable} should document any conditions under which suppression
* is disabled and document conditions under which the stack trace is not
* writable. Disabling of suppression should only occur in exceptional
* circumstances where special requirements exist, such as a virtual machine
* reusing exception objects under low-memory situations. Circumstances
* where a given exception object is repeatedly caught and rethrown, such as
* to implement control flow between two sub-systems, is another situation
* where immutable throwable objects would be appropriate.
*
* @param message
* the detail message.
* @param cause
* the cause. (A {@code null} value is permitted, and indicates
* that the cause is nonexistent or unknown.)
* @param enableSuppression
* whether or not suppression is enabled or disabled
* @param writableStackTrace
* whether or not the stack trace should be writable
*
* @see OutOfMemoryError
* @see NullPointerException
* @see ArithmeticException
* @since 1.7
*/
protected Throwable(String message, Throwable cause,
boolean enableSuppression, boolean writableStackTrace) {
if (writableStackTrace) {
fillInStackTrace();
} else {
stackTrace = null;
}
detailMessage = message;
this.cause = cause;
if (!enableSuppression)
suppressedExceptions = null;
}
/**
* Returns the detail message string of this throwable.
*
* @return the detail message string of this {@code Throwable} instance
* (which may be {@code null}).
*/
public String getMessage() {
return detailMessage;
}
/**
* Creates a localized description of this throwable. Subclasses may
* override this method in order to produce a locale-specific message. For
* subclasses that do not override this method, the default implementation
* returns the same result as {@code getMessage()}.
*
* @return The localized description of this throwable.
* @since JDK1.1
*/
public String getLocalizedMessage() {
return getMessage();
}
/**
* Returns the cause of this throwable or {@code null} if the cause is
* nonexistent or unknown. (The cause is the throwable that caused this
* throwable to get thrown.)
*
* <p>
* This implementation returns the cause that was supplied via one of the
* constructors requiring a {@code Throwable}, or that was set after
* creation with the {@link #initCause(Throwable)} method. While it is
* typically unnecessary to override this method, a subclass can override it
* to return a cause set by some other means. This is appropriate for a
* "legacy chained throwable" that predates the addition of chained
* exceptions to {@code Throwable}. Note that it is <i>not</i> necessary to
* override any of the {@code PrintStackTrace} methods, all of which invoke
* the {@code getCause} method to determine the cause of a throwable.
*
* @return the cause of this throwable or {@code null} if the cause is
* nonexistent or unknown.
* @since 1.4
*/
public synchronized Throwable getCause() {
return (cause == this ? null : cause);
}
/**
* Initializes the <i>cause</i> of this throwable to the specified value.
* (The cause is the throwable that caused this throwable to get thrown.)
*
* <p>
* This method can be called at most once. It is generally called from
* within the constructor, or immediately after creating the throwable. If
* this throwable was created with {@link #Throwable(Throwable)} or
* {@link #Throwable(String,Throwable)}, this method cannot be called even
* once.
*
* <p>
* An example of using this method on a legacy throwable type without other
* support for setting the cause is:
*
* <pre>
* try {
* lowLevelOp();
* } catch (LowLevelException le) {
* throw (HighLevelException) new HighLevelException().initCause(le); // Legacy
* // constructor
* }
* </pre>
*
* @param cause
* the cause (which is saved for later retrieval by the
* {@link #getCause()} method). (A {@code null} value is
* permitted, and indicates that the cause is nonexistent or
* unknown.)
* @return a reference to this {@code Throwable} instance.
* @throws IllegalArgumentException
* if {@code cause} is this throwable. (A throwable cannot be
* its own cause.)
* @throws IllegalStateException
* if this throwable was created with
* {@link #Throwable(Throwable)} or
* {@link #Throwable(String,Throwable)}, or this method has
* already been called on this throwable.
* @since 1.4
*/
public synchronized Throwable initCause(Throwable cause) {
if (this.cause != this)
throw new IllegalStateException("Can't overwrite cause");
if (cause == this)
throw new IllegalArgumentException("Self-causation not permitted");
this.cause = cause;
return this;
}
/**
* Returns a short description of this throwable. The result is the
* concatenation of:
* <ul>
* <li>the {@linkplain Class#getName() name} of the class of this object
* <li>": " (a colon and a space)
* <li>the result of invoking this object's {@link #getLocalizedMessage}
* method
* </ul>
* If {@code getLocalizedMessage} returns {@code null}, then just the class
* name is returned.
*
* @return a string representation of this throwable.
*/
public String toString() {
String s = getClass().getName();
String message = getLocalizedMessage();
return (message != null) ? (s + ": " + message) : s;
}
/**
* 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: <blockquote>
*
* <pre>
* java.lang.NullPointerException
* at MyClass.mash(MyClass.java:9)
* at MyClass.crunch(MyClass.java:6)
* at MyClass.main(MyClass.java:3)
* </pre>
*
* </blockquote> This example was produced by running the program:
*
* <pre>
* 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]);
* }
* }
* </pre>
*
* 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:
*
* <pre>
* 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
* </pre>
*
* 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:
*
* <pre>
* 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 {
* }
* </pre>
*
* As of release 7, the platform supports the notion of <i>suppressed
* exceptions</i> (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:
*
* <pre>
* Exception in thread "main" java.lang.Exception: Something happened
* at Foo.bar(Foo.java:10)
* at Foo.main(Foo.java:5)
* Suppressed: Resource$CloseFailException: Resource ID = 0
* at Resource.close(Resource.java:26)
* at Foo.bar(Foo.java:9)
* ... 1 more
* </pre>
*
* Note that the "... n more" notation is used on suppressed exceptions just
* at it is used on causes. Unlike causes, suppressed exceptions are
* indented beyond their "containing exceptions."
*
* <p>
* An exception can have both a cause and one or more suppressed exceptions:
*
* <pre>
* Exception in thread "main" java.lang.Exception: Main block
* at Foo3.main(Foo3.java:7)
* Suppressed: Resource$CloseFailException: Resource ID = 2
* at Resource.close(Resource.java:26)
* at Foo3.main(Foo3.java:5)
* Suppressed: Resource$CloseFailException: Resource ID = 1
* at Resource.close(Resource.java:26)
* at Foo3.main(Foo3.java:5)
* Caused by: java.lang.Exception: I did it
* at Foo3.main(Foo3.java:8)
* </pre>
*
* Likewise, a suppressed exception can have a cause:
*
* <pre>
* Exception in thread "main" java.lang.Exception: Main block
* at Foo4.main(Foo4.java:6)
* Suppressed: Resource2$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.<init>(Resource2.java:45)
* ... 2 more
* </pre>
*/
public void printStackTrace() {
printStackTrace(System.err);
}
/**
* Prints this throwable and its backtrace to the specified print stream.
*
* @param s
* {@code PrintStream} to use for output
*/
public void printStackTrace(PrintStream s) {
printStackTrace(new WrappedPrintStream(s));
}
private void printStackTrace(PrintStreamOrWriter s) {
// Guard against malicious overrides of Throwable.equals by
// using a Set with identity equality semantics.
Set<Throwable> dejaVu = Collections
.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
dejaVu.add(this);
synchronized (s.lock()) {
// Print our stack trace
s.println(this);
StackTraceElement[] trace = getOurStackTrace();
for (StackTraceElement traceElement : trace)
s.println("\tat " + traceElement);
// Print suppressed exceptions, if any
for (Throwable se : getSuppressed())
se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t",
dejaVu);
// Print cause, if any
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "",
dejaVu);
}
}
/**
* Print our stack trace as an enclosed exception for the specified stack
* trace.
*/
private void printEnclosedStackTrace(PrintStreamOrWriter s,
StackTraceElement[] enclosingTrace, String caption, String prefix,
Set<Throwable> 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();
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 : getSuppressed())
se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, prefix
+ "\t", dejaVu);
// Print cause, if any
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION,
prefix, dejaVu);
}
}
/**
* Prints this throwable and its backtrace to the specified print writer.
*
* @param s
* {@code PrintWriter} to use for output
* @since JDK1.1
*/
public void printStackTrace(PrintWriter s) {
printStackTrace(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);
}
}
/**
* Fills in the execution stack trace. This method records within this
* {@code Throwable} object information about the current state of the stack
* frames for the current thread.
*
* <p>
* If the stack trace of this {@code Throwable}
* {@linkplain Throwable#Throwable(String, Throwable, boolean, boolean) is
* not writable}, calling this method has no effect.
*
* @return a reference to this {@code Throwable} instance.
* @see java.lang.Throwable#printStackTrace()
*/
public synchronized Throwable fillInStackTrace() {
if (stackTrace != null || backtrace != null /* Out of protocol state */) {
fillInStackTrace(0);
stackTrace = UNASSIGNED_STACK;
}
return this;
}
private native Throwable fillInStackTrace(int dummy);
/**
* Provides programmatic access to the stack trace information printed by
* {@link #printStackTrace()}. Returns an array of stack trace elements,
* each representing one stack frame. The zeroth element of the array
* (assuming the array's length is non-zero) represents the top of the
* stack, which is the last method invocation in the sequence. Typically,
* this is the point at which this throwable was created and thrown. The
* last element of the array (assuming the array's length is non-zero)
* represents the bottom of the stack, which is the first method invocation
* in the sequence.
*
* <p>
* Some virtual machines may, under some circumstances, omit one or more
* stack frames from the stack trace. In the extreme case, a virtual machine
* that has no stack trace information concerning this throwable is
* permitted to return a zero-length array from this method. Generally
* speaking, the array returned by this method will contain one element for
* every frame that would be printed by {@code printStackTrace}. Writes to
* the returned array do not affect future calls to this method.
*
* @return an array of stack trace elements representing the stack trace
* pertaining to this throwable.
* @since 1.4
*/
public StackTraceElement[] getStackTrace() {
return getOurStackTrace().clone();
}
private synchronized StackTraceElement[] getOurStackTrace() {
// Initialize stack trace field with information from
// backtrace if this is the first call to this method
if (stackTrace == UNASSIGNED_STACK
|| (stackTrace == null && backtrace != null) /*
* Out of protocol
* state
*/) {
int depth = getStackTraceDepth();
stackTrace = new StackTraceElement[depth];
for (int i = 0; i < depth; i++)
stackTrace[i] = getStackTraceElement(i);
} else if (stackTrace == null) {
return UNASSIGNED_STACK;
}
return stackTrace;
}
/**
* Sets the stack trace elements that will be returned by
* {@link #getStackTrace()} and printed by {@link #printStackTrace()} and
* related methods.
*
* This method, which is designed for use by RPC frameworks and other
* advanced systems, allows the client to override the default stack trace
* that is either generated by {@link #fillInStackTrace()} when a throwable
* is constructed or deserialized when a throwable is read from a
* serialization stream.
*
* <p>
* If the stack trace of this {@code Throwable}
* {@linkplain Throwable#Throwable(String, Throwable, boolean, boolean) is
* not writable}, calling this method has no effect other than validating
* its argument.
*
* @param stackTrace
* the stack trace elements to be associated with this
* {@code Throwable}. The specified array is copied by this call;
* changes in the specified array after the method invocation
* returns will have no affect on this {@code Throwable}'s stack
* trace.
*
* @throws NullPointerException
* if {@code stackTrace} is {@code null} or if any of the
* elements of {@code stackTrace} are {@code null}
*
* @since 1.4
*/
public void setStackTrace(StackTraceElement[] stackTrace) {
// Validate argument
StackTraceElement[] defensiveCopy = stackTrace.clone();
for (int i = 0; i < defensiveCopy.length; i++) {
if (defensiveCopy[i] == null)
throw new NullPointerException("stackTrace[" + i + "]");
}
synchronized (this) {
if (this.stackTrace == null && // Immutable stack
backtrace == null) // Test for out of protocol state
return;
this.stackTrace = defensiveCopy;
}
}
/**
* Returns the number of elements in the stack trace (or 0 if the stack
* trace is unavailable).
*
* package-protection for use by SharedSecrets.
*/
native int getStackTraceDepth();
/**
* Returns the specified element of the stack trace.
*
* package-protection for use by SharedSecrets.
*
* @param index
* index of the element to return.
* @throws IndexOutOfBoundsException
* if {@code index < 0 ||
* index >= getStackTraceDepth() }
*/
native StackTraceElement getStackTraceElement(int index);
/**
* Reads a {@code Throwable} from a stream, enforcing well-formedness
* constraints on fields. Null entries and self-pointers are not allowed in
* the list of {@code suppressedExceptions}. Null entries are not allowed
* for stack trace elements. A null stack trace in the serial form results
* in a zero-length stack element array. A single-element stack trace whose
* entry is equal to {@code new StackTraceElement("",
* "", null, Integer.MIN_VALUE)} results in a {@code null}
* {@code stackTrace} field.
*
* Note that there are no constraints on the value the {@code cause} field
* can hold; both {@code null} and {@code this} are valid values for the
* field.
*/
private void readObject(ObjectInputStream s) throws IOException,
ClassNotFoundException {
s.defaultReadObject(); // read in all fields
if (suppressedExceptions != null) {
List<Throwable> suppressed = null;
if (suppressedExceptions.isEmpty()) {
// Use the sentinel for a zero-length list
suppressed = SUPPRESSED_SENTINEL;
} else { // Copy Throwables to new list
suppressed = new ArrayList<Throwable>(1);
for (Throwable t : suppressedExceptions) {
// Enforce constraints on suppressed exceptions in
// case of corrupt or malicious stream.
if (t == null)
throw new NullPointerException(NULL_CAUSE_MESSAGE);
if (t == this)
throw new IllegalArgumentException(
SELF_SUPPRESSION_MESSAGE);
suppressed.add(t);
}
}
suppressedExceptions = suppressed;
} // else a null suppressedExceptions field remains null
/*
* For zero-length stack traces, use a clone of UNASSIGNED_STACK rather
* than UNASSIGNED_STACK itself to allow identity comparison against
* UNASSIGNED_STACK in getOurStackTrace. The identity of
* UNASSIGNED_STACK in stackTrace indicates to the getOurStackTrace
* method that the stackTrace needs to be constructed from the
* information in backtrace.
*/
if (stackTrace != null) {
if (stackTrace.length == 0) {
stackTrace = UNASSIGNED_STACK.clone();
} else if (stackTrace.length == 1 &&
// Check for the marker of an immutable stack trace
SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL
.equals(stackTrace[0])) {
stackTrace = null;
} else { // Verify stack trace elements are non-null.
for (StackTraceElement ste : stackTrace) {
if (ste == null)
throw new NullPointerException(
"null StackTraceElement in serial stream. ");
}
}
} else {
// A null stackTrace field in the serial form can result
// from an exception serialized without that field in
// older JDK releases; treat such exceptions as having
// empty stack traces.
stackTrace = UNASSIGNED_STACK.clone();
}
}
/**
* Write a {@code Throwable} object to a stream.
*
* A {@code null} stack trace field is represented in the serial form as a
* one-element array whose element is equal to
* {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
*/
private synchronized void writeObject(ObjectOutputStream s)
throws IOException {
// Ensure that the stackTrace field is initialized to a
// non-null value, if appropriate. As of JDK 7, a null stack
// trace field is a valid value indicating the stack trace
// should not be set.
getOurStackTrace();
StackTraceElement[] oldStackTrace = stackTrace;
try {
if (stackTrace == null)
stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
s.defaultWriteObject();
} finally {
stackTrace = oldStackTrace;
}
}
/**
* Appends the specified exception to the exceptions that were suppressed in
* order to deliver this exception. This method is thread-safe and typically
* called (automatically and implicitly) by the {@code try}-with-resources
* statement.
*
* <p>
* The suppression behavior is enabled <em>unless</em> disabled
* {@linkplain #Throwable(String, Throwable, boolean, boolean) via a
* constructor}. When suppression is disabled, this method does nothing
* other than to validate its argument.
*
* <p>
* Note that when one exception {@linkplain #initCause(Throwable) causes}
* another exception, the first exception is usually caught and then the
* second exception is thrown in response. In other words, there is a causal
* connection between the two exceptions.
*
* In contrast, there are situations where two independent exceptions can be
* thrown in sibling code blocks, in particular in the {@code try} block of
* a {@code try}-with-resources statement and the compiler-generated
* {@code finally} block which closes the resource.
*
* In these situations, only one of the thrown exceptions can be propagated.
* In the {@code try}-with-resources statement, when there are two such
* exceptions, the exception originating from the {@code try} block is
* propagated and the exception from the {@code finally} block is added to
* the list of exceptions suppressed by the exception from the {@code try}
* block. As an exception unwinds the stack, it can accumulate multiple
* suppressed exceptions.
*
* <p>
* An exception may have suppressed exceptions while also being caused by
* another exception. Whether or not an exception has a cause is
* semantically known at the time of its creation, unlike whether or not an
* exception will suppress other exceptions which is typically only
* determined after an exception is thrown.
*
* <p>
* Note that programmer written code is also able to take advantage of
* calling this method in situations where there are multiple sibling
* exceptions and only one can be propagated.
*
* @param exception
* the exception to be added to the list of suppressed exceptions
* @throws IllegalArgumentException
* if {@code exception} is this throwable; a throwable cannot
* suppress itself.
* @throws NullPointerException
* if {@code exception} is {@code null}
* @since 1.7
*/
public final synchronized void addSuppressed(Throwable exception) {
if (exception == this)
throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
if (exception == null)
throw new NullPointerException(NULL_CAUSE_MESSAGE);
if (suppressedExceptions == null) // Suppressed exceptions not recorded
return;
if (suppressedExceptions == SUPPRESSED_SENTINEL)
suppressedExceptions = new ArrayList<Throwable>(1);
suppressedExceptions.add(exception);
}
private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];
/**
* Returns an array containing all of the exceptions that were suppressed,
* typically by the {@code try}-with-resources statement, in order to
* deliver this exception.
*
* If no exceptions were suppressed or
* {@linkplain #Throwable(String, Throwable, boolean, boolean) suppression
* is disabled}, an empty array is returned. This method is thread-safe.
* Writes to the returned array do not affect future calls to this method.
*
* @return an array containing all of the exceptions that were suppressed to
* deliver this exception.
* @since 1.7
*/
public final synchronized Throwable[] getSuppressed() {
if (suppressedExceptions == SUPPRESSED_SENTINEL
|| suppressedExceptions == null)
return EMPTY_THROWABLE_ARRAY;
else
return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
}
}