/*
* @(#)Throwable.java 1.53 03/12/19
*
* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
*/
package java.lang;
import java.io.*;
/**
* The <code>Throwable</code> 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</code> statement. Similarly, only
* this class or one of its subclasses can be the argument type in a
* <code>catch</code> clause.
*
* <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. Finally, it can contain a <i>cause</i>:
* another throwable that caused this throwable to get thrown. The cause
* facility is new in release 1.4. It is also known 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
* <tt>java.io</tt>. Suppose the internals of the <tt>put</tt> method
* can throw an {@link java.io.IOException IOException}. The implementation
* can communicate the details of the <tt>IOException</tt> to its caller
* while conforming to the <tt>Collection</tt> interface by wrapping the
* <tt>IOException</tt> 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
* <tt>Throwable</tt> constructors that takes a cause. For example:
* <pre>
* try {
* lowLevelOp();
* } catch (LowLevelException le) {
* throw new HighLevelException(le); // Chaining-aware constructor
* }
* </pre>
* Because the <tt>initCause</tt> 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
* <tt>Throwable</tt>. For example:
* <pre>
* try {
* lowLevelOp();
* } catch (LowLevelException le) {
* throw (HighLevelException)
new HighLevelException().initCause(le); // Legacy constructor
* }
* </pre>
*
* <p>Prior to release 1.4, there were many throwables that had their own
* non-standard exception chaining mechanisms (
* {@link ExceptionInInitializerError}, {@link ClassNotFoundException},
* {@link java.lang.reflect.UndeclaredThrowableException},
* {@link java.lang.reflect.InvocationTargetException},
* {@link java.io.WriteAbortedException},
* {@link java.security.PrivilegedActionException},
* {@link java.awt.print.PrinterIOException},
* {@link java.rmi.RemoteException} and
* {@link javax.naming.NamingException}).
* All of these throwables have been retrofitted to
* use the standard exception chaining mechanism, while continuing to
* implement their "legacy" chaining mechanisms for compatibility.
*
* <p>Further, as of release 1.4, many general purpose <tt>Throwable</tt>
* classes (for example {@link Exception}, {@link RuntimeException},
* {@link Error}) have been retrofitted with constructors that take
* a cause. This was not strictly necessary, due to the existence of the
* <tt>initCause</tt> method, but it is more convenient and expressive to
* delegate to a constructor that takes a cause.
*
* <p>By convention, class <code>Throwable</code> and its subclasses have two
* constructors, one that takes no arguments and one that takes a
* <code>String</code> 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</code> (the cause), and one that takes a
* <code>String</code> (the detail message) and a <code>Throwable</code> (the
* cause).
*
* <p>Also introduced in release 1.4 is the {@link #getStackTrace()} method,
* which allows programmatic access to the stack trace information that was
* previously available only in text form, via the various forms of the
* {@link #printStackTrace()} method. This information has been added to the
* <i>serialized representation</i> of this class so <tt>getStackTrace</tt>
* and <tt>printStackTrace</tt> will operate properly on a throwable that
* was obtained by deserialization.
*
* @author unascribed
* @author Josh Bloch (Added exception chaining and programmatic access to
* stack trace in 1.4.)
* @version 1.53, 12/19/03
* @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
* <tt>FileNotFoundException</tt>, this contains the name of
* the file that could not be found.
*
* @serial
*/
private String detailMessage;
/**
* 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()}.
*
* @serial
* @since 1.4
*/
private StackTraceElement[] stackTrace;
/*
* This field is lazily initialized on first use or serialization and
* nulled out when fillInStackTrace is called.
*/
/**
* Constructs a new throwable with <code>null</code> 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</code> 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 <tt>null</tt> 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 <tt>(cause==null ? null : cause.toString())</tt> (which
* typically contains the class and detail message of <tt>cause</tt>).
* 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 <tt>null</tt> 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;
}
/**
* Returns the detail message string of this throwable.
*
* @return the detail message string of this <tt>Throwable</tt> instance
* (which may be <tt>null</tt>).
*/
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()</code>.
*
* @return The localized description of this throwable.
* @since JDK1.1
*/
public String getLocalizedMessage() {
return getMessage();
}
/**
* Returns the cause of this throwable or <code>null</code> 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 <tt>Throwable</tt>, 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 <tt>Throwable</tt>. Note that it is <i>not</i>
* necessary to override any of the <tt>PrintStackTrace</tt> methods,
* all of which invoke the <tt>getCause</tt> method to determine the
* cause of a throwable.
*
* @return the cause of this throwable or <code>null</code> if the
* cause is nonexistent or unknown.
* @since 1.4
*/
public 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.
*
* @param cause the cause (which is saved for later retrieval by the
* {@link #getCause()} method). (A <tt>null</tt> value is
* permitted, and indicates that the cause is nonexistent or
* unknown.)
* @return a reference to this <code>Throwable</code> instance.
* @throws IllegalArgumentException if <code>cause</code> 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.
* If this <code>Throwable</code> object was created with a non-null detail
* message string, then the result is the concatenation of three strings:
* <ul>
* <li>The name of the actual class of this object
* <li>": " (a colon and a space)
* <li>The result of the {@link #getMessage} method for this object
* </ul>
* If this <code>Throwable</code> object was created with a <tt>null</tt>
* detail message string, then the name of the actual class of this object
* 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</code> object on the error output stream that is
* the value of the field <code>System.err</code>. 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 <tt>"..."</tt>.
* 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>
*/
public void printStackTrace() {
printStackTrace(System.err);
}
/**
* Prints this throwable and its backtrace to the specified print stream.
*
* @param s <code>PrintStream</code> to use for output
*/
public void printStackTrace(PrintStream s) {
synchronized (s) {
s.println(this);
StackTraceElement[] trace = getOurStackTrace();
for (int i=0; i < trace.length; i++)
s.println("\tat " + trace[i]);
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
}
/**
* Print our stack trace as a cause for the specified stack trace.
*/
private void printStackTraceAsCause(PrintStream s,
StackTraceElement[] causedTrace)
{
// assert Thread.holdsLock(s);
// Compute number of frames in common between this and caused
StackTraceElement[] trace = getOurStackTrace();
int m = trace.length-1, n = causedTrace.length-1;
while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) {
m--; n--;
}
int framesInCommon = trace.length - 1 - m;
s.println("Caused by: " + this);
for (int i=0; i <= m; i++)
s.println("\tat " + trace[i]);
if (framesInCommon != 0)
s.println("\t... " + framesInCommon + " more");
// Recurse if we have a cause
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
/**
* Prints this throwable and its backtrace to the specified
* print writer.
*
* @param s <code>PrintWriter</code> to use for output
* @since JDK1.1
*/
public void printStackTrace(PrintWriter s) {
synchronized (s) {
s.println(this);
StackTraceElement[] trace = getOurStackTrace();
for (int i=0; i < trace.length; i++)
s.println("\tat " + trace[i]);
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
}
/**
* Print our stack trace as a cause for the specified stack trace.
*/
private void printStackTraceAsCause(PrintWriter s,
StackTraceElement[] causedTrace)
{
// assert Thread.holdsLock(s);
// Compute number of frames in common between this and caused
StackTraceElement[] trace = getOurStackTrace();
int m = trace.length-1, n = causedTrace.length-1;
while (m >= 0 && n >=0 && trace[m].equals(causedTrace[n])) {
m--; n--;
}
int framesInCommon = trace.length - 1 - m;
s.println("Caused by: " + this);
for (int i=0; i <= m; i++)
s.println("\tat " + trace[i]);
if (framesInCommon != 0)
s.println("\t... " + framesInCommon + " more");
// Recurse if we have a cause
Throwable ourCause = getCause();
if (ourCause != null)
ourCause.printStackTraceAsCause(s, trace);
}
/**
* Fills in the execution stack trace. This method records within this
* <code>Throwable</code> object information about the current state of
* the stack frames for the current thread.
*
* @return a reference to this <code>Throwable</code> instance.
* @see java.lang.Throwable#printStackTrace()
*/
public synchronized native Throwable fillInStackTrace();
/**
* 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
* <tt>printStackTrace</tt>.
*
* @return an array of stack trace elements representing the stack trace
* pertaining to this throwable.
* @since 1.4
*/
public StackTraceElement[] getStackTrace() {
return (StackTraceElement[]) getOurStackTrace().clone();
}
private synchronized StackTraceElement[] getOurStackTrace() {
// Initialize stack trace if this is the first call to this method
if (stackTrace == null) {
int depth = getStackTraceDepth();
stackTrace = new StackTraceElement[depth];
for (int i=0; i < depth; i++)
stackTrace[i] = getStackTraceElement(i);
}
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.
*
* @param stackTrace the stack trace elements to be associated with
* this <code>Throwable</code>. 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</code>'s stack
* trace.
*
* @throws NullPointerException if <code>stackTrace</code> is
* <code>null</code>, or if any of the elements of
* <code>stackTrace</code> are <code>null</code>
*
* @since 1.4
*/
public void setStackTrace(StackTraceElement[] stackTrace) {
StackTraceElement[] defensiveCopy =
(StackTraceElement[]) stackTrace.clone();
for (int i = 0; i < defensiveCopy.length; i++)
if (defensiveCopy[i] == null)
throw new NullPointerException("stackTrace[" + i + "]");
this.stackTrace = defensiveCopy;
}
/**
* Returns the number of elements in the stack trace (or 0 if the stack
* trace is unavailable).
*/
private native int getStackTraceDepth();
/**
* Returns the specified element of the stack trace.
*
* @param index index of the element to return.
* @throws IndexOutOfBoundsException if <tt>index %lt; 0 ||
* index >= getStackTraceDepth() </tt>
*/
private native StackTraceElement getStackTraceElement(int index);
private synchronized void writeObject(java.io.ObjectOutputStream s)
throws IOException
{
getOurStackTrace(); // Ensure that stackTrace field is initialized.
s.defaultWriteObject();
}
}
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