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 <body-content> 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 {
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 }