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Tomcat example source code file (IterationTag.java)

This example Tomcat source code file (IterationTag.java) is included in the DevDaily.com "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 IterationTag.java 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
*
*     http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* 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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