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Java > Open Source Codes > javax > servlet > jsp > tagext > IterationTag


1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18 package javax.servlet.jsp.tagext;
19
20 import javax.servlet.jsp.*;
21
22 /**
23  * The IterationTag interface extends Tag by defining one additional
24  * method that controls the reevaluation of its body.
25  *
26  * <p> A tag handler that implements IterationTag is treated as one that
27  * implements Tag regarding the doStartTag() and doEndTag() methods.
28  * IterationTag provides a new method: <code>doAfterBody()</code>.
29  *
30  * <p> The doAfterBody() method is invoked after every body evaluation
31  * to control whether the body will be reevaluated or not. If doAfterBody()
32  * returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated.
33  * If doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped
34  * and doEndTag() will be evaluated instead.
35  *
36  * <p><B>Properties</B>
37  * There are no new properties in addition to those in Tag.
38  *
39  * <p><B>Methods</B>
40  * There is one new methods: doAfterBody().
41  *
42  * <p><B>Lifecycle</B>
43  *
44  * <p> Lifecycle details are described by the transition diagram
45  * below. Exceptions that are thrown during the computation of
46  * doStartTag(), BODY and doAfterBody() interrupt the execution
47  * sequence and are propagated up the stack, unless the tag handler
48  * implements the TryCatchFinally interface; see that interface for
49  * details.
50  *
51  * <p>
52  * <IMG SRC="doc-files/IterationTagProtocol.gif"
53  * alt="Lifecycle Details Transition Diagram for IterationTag"/>
54  *
55  * <p><B>Empty and Non-Empty Action</B>
56  * <p> If the TagLibraryDescriptor file indicates that the action must
57  * always have an empty element body, by a &lt;body-content&gt; entry of
58  * "empty", then the doStartTag() method must return SKIP_BODY.
59  *
60  * <p>Note that which methods are invoked after the doStartTag() depends on
61  * both the return value and on if the custom action element is empty
62  * or not in the JSP page, not on how it's declared in the TLD.
63  *
64  * <p>
65  * If SKIP_BODY is returned the body is not evaluated, and then doEndTag()
66  * is invoked.
67  *
68  * <p>
69  * If EVAL_BODY_INCLUDE is returned, and the custom action element is not
70  * empty, the body is evaluated and "passed through" to the current out,
71  * then doAfterBody() is invoked and, after zero or more iterations,
72  * doEndTag() is invoked.
73  */
74
75 public interface IterationTag extends Tag JavaDoc {
76
77     /**
78      * Request the reevaluation of some body.
79      * Returned from doAfterBody.
80      *
81      * For compatibility with JSP 1.1, the value is carefully selected
82      * to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
83      *
84      */
85  
86     public final static int EVAL_BODY_AGAIN = 2;
87
88     /**
89      * Process body (re)evaluation. This method is invoked by the
90      * JSP Page implementation object after every evaluation of
91      * the body into the BodyEvaluation object. The method is
92      * not invoked if there is no body evaluation.
93      *
94      * <p>
95      * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the
96      * body will happen (followed by another invocation of doAfterBody).
97      * If doAfterBody returns SKIP_BODY, no more body evaluations will occur,
98      * and the doEndTag method will be invoked.
99      *
100      * <p>
101      * If this tag handler implements BodyTag and doAfterBody returns
102      * SKIP_BODY, the value of out will be restored using the popBody
103      * method in pageContext prior to invoking doEndTag.
104      *
105      * <p>
106      * The method re-invocations may be lead to different actions because
107      * there might have been some changes to shared state, or because
108      * of external computation.
109      *
110      * <p>
111      * The JSP container will resynchronize the values of any AT_BEGIN and
112      * NESTED variables (defined by the associated TagExtraInfo or TLD) after
113      * the invocation of doAfterBody().
114      *
115      * @return whether additional evaluations of the body are desired
116      * @throws JspException if an error occurred while processing this tag
117      */
118
119     int doAfterBody() throws JspException;
120 }
121
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