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TryCatchFinally (JavaServer Pages API Documentation)

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javax.servlet.jsp.tagext
Interface TryCatchFinally

public interface TryCatchFinally

The auxiliary interface of a Tag, IterationTag or BodyTag tag handler that wants additional hooks for managing resources.

This interface provides two new methods: doCatch(Throwable) and doFinally(). The prototypical invocation is as follows:

 h = get a Tag();  // get a tag handler, perhaps from pool

 h.setPageContext(pc);  // initialize as desired
 h.setParent(null);
 h.setFoo("foo");
 
 // tag invocation protocol; see Tag.java
 try {
   doStartTag()...
   ....
   doEndTag()...
 } catch (Throwable t) {
   // react to exceptional condition
   h.doCatch(t);
 } finally {
   // restore data invariants and release per-invocation resources
   h.doFinally();
 }
 
 ... other invocations perhaps with some new setters
 ...
 h.release();  // release long-term resources

Method Summary

void doCatch(java.lang.Throwable t)
Invoked if a Throwable occurs while evaluating the BODY inside a tag or in any of the following methods: Tag.doStartTag(), Tag.doEndTag(), IterationTag.doAfterBody() and BodyTag.doInitBody().

void doFinally()
Invoked in all cases after doEndTag() for any class implementing Tag, IterationTag or BodyTag.

Method Detail

doCatch

public void doCatch(java.lang.Throwable t)
             throws java.lang.Throwable

Invoked if a Throwable occurs while evaluating the BODY inside a tag or in any of the following methods: Tag.doStartTag(), Tag.doEndTag(), IterationTag.doAfterBody() and BodyTag.doInitBody().

This method is not invoked if the Throwable occurs during one of the setter methods.

This method may throw an exception (the same or a new one) that will be propagated further up the nest chain. If an exception is thrown, doFinally() will be invoked.

This method is intended to be used to respond to an exceptional condition.

Parameters:: t - The throwable exception navigating through this tag.
Throws:: java.lang.Throwable - if the exception is to be rethrown further up the nest chain.

doFinally

public void doFinally()

Invoked in all cases after doEndTag() for any class implementing Tag, IterationTag or BodyTag. This method is invoked even if an exception has occurred in the BODY of the tag, or in any of the following methods: Tag.doStartTag(), Tag.doEndTag(), IterationTag.doAfterBody() and BodyTag.doInitBody().

This method is not invoked if the Throwable occurs during one of the setter methods.

This method should not throw an Exception.

This method is intended to maintain per-invocation data integrity and resource management actions.