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Tomcat example source code file (

This example Tomcat source code file ( is included in the "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Tomcat tags/keywords

eval_body_again, eval_body_again, http, iterationtag, iterationtag, jspexception, jspexception, servlet, tag, tag

The Tomcat source code

* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements.  See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License.  You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.

package javax.servlet.jsp.tagext;

import javax.servlet.jsp.*;

 * The IterationTag interface extends Tag by defining one additional
 * method that controls the reevaluation of its body.
 * <p> A tag handler that implements IterationTag is treated as one that
 * implements Tag regarding  the doStartTag() and doEndTag() methods.
 * IterationTag provides a new method: <code>doAfterBody().
 * <p> 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.
 * <p>Properties
 * There are no new properties in addition to those in Tag.
 * <p>Methods
 * There is one new methods: doAfterBody().
 * <p>Lifecycle
 * <p> 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.
 * <p>
 * <IMG src="doc-files/IterationTagProtocol.gif"
 *      alt="Lifecycle Details Transition Diagram for IterationTag"/>
 * <p>Empty and Non-Empty Action
 * <p> 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.
 * <p>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.
 * <p>
 * If SKIP_BODY is returned the body is not evaluated, and then doEndTag()
 * is invoked.
 * <p>
 * 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.

public interface IterationTag extends Tag {

     * 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,
    public final static int EVAL_BODY_AGAIN = 2;

     * 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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * 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.
     * <p>
     * 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().
     * @return whether additional evaluations of the body are desired
     * @throws JspException if an error occurred while processing this tag

    int doAfterBody() throws JspException;

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