An application often responds to an exception by throwing another exception. In effect, the first exception causes the second exception. It can be very helpful to know when one exception causes another. Chained Exceptions help the programmer do this.The following are the methods and constructors in
Throwable
that support chained exceptions.TheThrowable getCause() Throwable initCause(Throwable) Throwable(String, Throwable) Throwable(Throwable)Throwable
argument toinitCause
and theThrowable
constructors is the exception that caused the current exception.getCause
returns the exception that caused the current exception, andinitCause
returns the current exception.The following example shows how to use a chained exception.
In this example, when antry { } catch (IOException e) { throw new SampleException("Other IOException", e); }IOException
is caught, a newSampleException
exception is created with the original cause attached and the chain of exceptions is thrown up to the next higher level exception handler.Accessing Stack Trace Information
Now let's suppose that the higher-level exception handler wants to dump the stack trace in its own format.The following code shows how to call the
Definition: A stack trace provides information on the execution history of the current thread and lists the names of the classes and methods that were called at the point when the exception occurred. A stack trace is a useful debugging tool that you'll normally take advantage of when an exception has been thrown.getStackTrace
method on the exception object.catch (Exception cause) { StackTraceElement elements[] = cause.getStackTrace(); for (int i = 0, n = elements.length; i < n; i++) { System.err.println(elements[i].getFileName() + ":" + elements[i].getLineNumber() + ">> " + elements[i].getMethodName() + "()"); } }Logging API
The next code snippet logs where an exception occurred from within thecatch
block. However, rather than manually parsing the stack trace and sending the output toSystem.err()
, it sends the output to a file using the logging facility in thejava.util.logging
package.try { Handler handler = new FileHandler("OutFile.log"); Logger.getLogger("").addHandler(handler); } catch (IOException e) { Logger logger = Logger.getLogger("package.name"); StackTraceElement elements[] = e.getStackTrace(); for (int i = 0, n = elements.length; i < n; i++) { logger.log(Level.WARNING, elements[i].getMethodName()); } }