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IterationTag (JavaServer Pages API Documentation)

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javax.servlet.jsp.tagext
Interface IterationTag

All Superinterfaces:: JspTag, Tag

All Known Subinterfaces:: BodyTag

All Known Implementing Classes:: BodyTagSupport, TagSupport

public interface IterationTag
extends Tag

The IterationTag interface extends Tag by defining one additional method that controls the reevaluation of its body.

A tag handler that implements IterationTag is treated as one that implements Tag regarding the doStartTag() and doEndTag() methods. IterationTag provides a new method: doAfterBody().

The doAfterBody() method is invoked after every body evaluation to control whether the body will be reevaluated or not. If doAfterBody() returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated. If doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped and doEndTag() will be evaluated instead.

Properties There are no new properties in addition to those in Tag.

Methods There is one new methods: doAfterBody().

Lifecycle

Lifecycle details are described by the transition diagram below. Exceptions that are thrown during the computation of doStartTag(), BODY and doAfterBody() interrupt the execution sequence and are propagated up the stack, unless the tag handler implements the TryCatchFinally interface; see that interface for details.

Lifecycle Details Transition Diagram for IterationTag

Empty and Non-Empty Action

If the TagLibraryDescriptor file indicates that the action must always have an empty element body, by a <body-content> entry of "empty", then the doStartTag() method must return SKIP_BODY.

Note that which methods are invoked after the doStartTag() depends on both the return value and on if the custom action element is empty or not in the JSP page, not on how it's declared in the TLD.

If SKIP_BODY is returned the body is not evaluated, and then doEndTag() is invoked.

If EVAL_BODY_INCLUDE is returned, and the custom action element is not empty, the body is evaluated and "passed through" to the current out, then doAfterBody() is invoked and, after zero or more iterations, doEndTag() is invoked.

Field Summary

static int EVAL_BODY_AGAIN
Request the reevaluation of some body.

Fields inherited from interface javax.servlet.jsp.tagext.Tag

EVAL_BODY_INCLUDE, EVAL_PAGE, SKIP_BODY, SKIP_PAGE

Method Summary

int doAfterBody()
Process body (re)evaluation.

Methods inherited from interface javax.servlet.jsp.tagext.Tag

doEndTag, doStartTag, getParent, release, setPageContext, setParent

Field Detail

EVAL_BODY_AGAIN

public static final int EVAL_BODY_AGAIN

Request the reevaluation of some body. Returned from doAfterBody. For compatibility with JSP 1.1, the value is carefully selected to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,

See Also:: Constant Field Values

Method Detail

doAfterBody

public int doAfterBody()
                throws JspException

Process body (re)evaluation. This method is invoked by the JSP Page implementation object after every evaluation of the body into the BodyEvaluation object. The method is not invoked if there is no body evaluation.

If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the body will happen (followed by another invocation of doAfterBody). If doAfterBody returns SKIP_BODY, no more body evaluations will occur, and the doEndTag method will be invoked.

If this tag handler implements BodyTag and doAfterBody returns SKIP_BODY, the value of out will be restored using the popBody method in pageContext prior to invoking doEndTag.

The method re-invocations may be lead to different actions because there might have been some changes to shared state, or because of external computation.

The JSP container will resynchronize the values of any AT_BEGIN and NESTED variables (defined by the associated TagExtraInfo or TLD) after the invocation of doAfterBody().