001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *  http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing,
013     * software distributed under the License is distributed on an
014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     * KIND, either express or implied.  See the License for the
016     * specific language governing permissions and limitations
017     * under the License.
018     */
019    
020    //
021    // This source code implements specifications defined by the Java
022    // Community Process. In order to remain compliant with the specification
023    // DO NOT add / change / or delete method signatures!
024    //
025    
026    package javax.servlet.jsp.tagext;
027    
028    import javax.servlet.jsp.*;
029    
030    /**
031     * The IterationTag interface extends Tag by defining one additional
032     * method that controls the reevaluation of its body.
033     *
034     * <p> A tag handler that implements IterationTag is treated as one that
035     * implements Tag regarding  the doStartTag() and doEndTag() methods.
036     * IterationTag provides a new method: <code>doAfterBody()</code>.
037     *
038     * <p> The doAfterBody() method is invoked after every body evaluation
039     * to control whether the body will be reevaluated or not.  If doAfterBody()
040     * returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated.
041     * If doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped
042     * and doEndTag() will be evaluated instead.
043     *
044     * <p><B>Properties</B>
045     * There are no new properties in addition to those in Tag.
046     *
047     * <p><B>Methods</B>
048     * There is one new methods: doAfterBody().
049     *
050     * <p><B>Lifecycle</B>
051     *
052     * <p> Lifecycle details are described by the transition diagram
053     * below.  Exceptions that are thrown during the computation of
054     * doStartTag(), BODY and doAfterBody() interrupt the execution
055     * sequence and are propagated up the stack, unless the tag handler
056     * implements the TryCatchFinally interface; see that interface for
057     * details.
058     *
059     * <p>
060     * <IMG src="doc-files/IterationTagProtocol.gif"
061     *      alt="Lifecycle Details Transition Diagram for IterationTag"/>
062     *
063     * <p><B>Empty and Non-Empty Action</B>
064     * <p> If the TagLibraryDescriptor file indicates that the action must
065     * always have an empty element body, by a &lt;body-content&gt; entry of 
066     * "empty", then the doStartTag() method must return SKIP_BODY.
067     *
068     * <p>Note that which methods are invoked after the doStartTag() depends on
069     * both the return value and on if the custom action element is empty
070     * or not in the JSP page, not on how it's declared in the TLD.
071     *
072     * <p>
073     * If SKIP_BODY is returned the body is not evaluated, and then doEndTag()
074     * is invoked.
075     *
076     * <p>
077     * If EVAL_BODY_INCLUDE is returned, and the custom action element is not
078     * empty, the body is evaluated and "passed through" to the current out, 
079     * then doAfterBody() is invoked and, after zero or more iterations, 
080     * doEndTag() is invoked.
081     */
082    
083    public interface IterationTag extends Tag {
084    
085        /**
086         * Request the reevaluation of some body.
087         * Returned from doAfterBody.
088         *
089         * For compatibility with JSP 1.1, the value is carefully selected
090         * to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
091         * 
092         */
093     
094        public final static int EVAL_BODY_AGAIN = 2;
095    
096        /**
097         * Process body (re)evaluation.  This method is invoked by the
098         * JSP Page implementation object after every evaluation of
099         * the body into the BodyEvaluation object. The method is
100         * not invoked if there is no body evaluation.
101         *
102         * <p>
103         * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the
104         * body will happen (followed by another invocation of doAfterBody).
105         * If doAfterBody returns SKIP_BODY, no more body evaluations will occur,
106         * and the doEndTag method will be invoked.
107         *
108         * <p>
109         * If this tag handler implements BodyTag and doAfterBody returns
110         * SKIP_BODY, the value of out will be restored using the popBody 
111         * method in pageContext prior to invoking doEndTag.
112         *
113         * <p>
114         * The method re-invocations may be lead to different actions because
115         * there might have been some changes to shared state, or because
116         * of external computation.
117         *
118         * <p>
119         * The JSP container will resynchronize the values of any AT_BEGIN and
120         * NESTED variables (defined by the associated TagExtraInfo or TLD) after
121         * the invocation of doAfterBody().
122         *
123         * @return whether additional evaluations of the body are desired
124         * @throws JspException if an error occurred while processing this tag
125         */
126    
127        int doAfterBody() throws JspException;
128    }