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Could you tell me about chain exceptions?

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Question: Could you tell me about chain exceptions?

Answer: It is common for Java code to catch one exception and throw another:
try {
...
} catch(YourException e) {
throw new MyException();
}

Unfortunately, the information contained in the "causative exception" (YourException in the example above) is generally lost, which greatly complicates debugging.

The version 1.4 libraries add a unified, general-purpose mechanism to record such information. The preexisting ad-hoc facilities have been retrofitted to use the new technique. Two new constructors were added to Throwable. Each takes another Throwable as the cause.

Throwable(Throwable cause)
Throwable(String message, Throwable cause)

Common exceptions classes have had analogous new constructors added. The intended usage is:
try {
lowLevelOp();
} catch (LowLevelException le) {
throw new HighLevelException(le);
}

Legacy exception classes can use a modified form of new idiom through the Throwable initCause(Throwable cause) method, such as:

try {
lowLevelOp();
} catch (LowLevelException le) {
throw new (HighLevelException)
HighLevelException().initCause(le);
}

The cause information can be retrieved through the method Throwable getCause().
For more information, see: http://java.sun.com/j2se/1.4/docs/guide/lang/chainedexceptions.html

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