1 /**
2 *
3 * Copyright 2003-2004 The Apache Software Foundation
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * 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 //
19 // This source code implements specifications defined by the Java
20 // Community Process. In order to remain compliant with the specification
21 // DO NOT add / change / or delete method signatures!
22 //
23
24 package javax.servlet.jsp.tagext;
25
26 import javax.servlet.jsp.JspException;
27
28 /**
29 * The IterationTag interface extends Tag by defining one additional
30 * method that controls the reevaluation of its body.
31 *
32 * <p> A tag handler that implements IterationTag is treated as one that
33 * implements Tag regarding the doStartTag() and doEndTag() methods.
34 * IterationTag provides a new method: <code>doAfterBody()</code>.
35 *
36 * <p> The doAfterBody() method is invoked after every body evaluation
37 * to control whether the body will be reevaluated or not. If doAfterBody()
38 * returns IterationTag.EVAL_BODY_AGAIN, then the body will be reevaluated.
39 * If doAfterBody() returns Tag.SKIP_BODY, then the body will be skipped
40 * and doEndTag() will be evaluated instead.
41 *
42 * <p><B>Properties</B>
43 * There are no new properties in addition to those in Tag.
44 *
45 * <p><B>Methods</B>
46 * There is one new methods: doAfterBody().
47 *
48 * <p><B>Lifecycle</B>
49 *
50 * <p> Lifecycle details are described by the transition diagram
51 * below. Exceptions that are thrown during the computation of
52 * doStartTag(), BODY and doAfterBody() interrupt the execution
53 * sequence and are propagated up the stack, unless the tag handler
54 * implements the TryCatchFinally interface; see that interface for
55 * details.
56 *
57 * <p>
58 * <IMG src="doc-files/IterationTagProtocol.gif"
59 * alt="Lifecycle Details Transition Diagram for IterationTag"/>
60 *
61 * <p><B>Empty and Non-Empty Action</B>
62 * <p> If the TagLibraryDescriptor file indicates that the action must
63 * always have an empty element body, by a <body-_content> entry of
64 * "empty", then the doStartTag() method must return SKIP_BODY.
65 *
66 * <p>Note that which methods are invoked after the doStartTag() depends on
67 * both the return value and on if the custom action element is empty
68 * or not in the JSP page, not on how it's declared in the TLD.
69 *
70 * <p>
71 * If SKIP_BODY is returned the body is not evaluated, and then doEndTag()
72 * is invoked.
73 *
74 * <p>
75 * If EVAL_BODY_INCLUDE is returned, and the custom action element is not
76 * empty, the body is evaluated and "passed through" to the current out,
77 * then doAfterBody() is invoked and, after zero or more iterations,
78 * doEndTag() is invoked.
79 */
80
81 public interface IterationTag extends Tag {
82
83 /**
84 * Request the reevaluation of some body.
85 * Returned from doAfterBody.
86 *
87 * For compatibility with JSP 1.1, the value is carefully selected
88 * to be the same as the, now deprecated, BodyTag.EVAL_BODY_TAG,
89 *
90 */
91
92 public final static int EVAL_BODY_AGAIN = 2;
93
94 /**
95 * Process body (re)evaluation. This method is invoked by the
96 * JSP Page implementation object after every evaluation of
97 * the body into the BodyEvaluation object. The method is
98 * not invoked if there is no body evaluation.
99 *
100 * <p>
101 * If doAfterBody returns EVAL_BODY_AGAIN, a new evaluation of the
102 * body will happen (followed by another invocation of doAfterBody).
103 * If doAfterBody returns SKIP_BODY, no more body evaluations will occur,
104 * and the doEndTag method will be invoked.
105 *
106 * <p>
107 * If this tag handler implements BodyTag and doAfterBody returns
108 * SKIP_BODY, the value of out will be restored using the popBody
109 * method in pageContext prior to invoking doEndTag.
110 *
111 * <p>
112 * The method re-invocations may be lead to different actions because
113 * there might have been some changes to shared state, or because
114 * of external computation.
115 *
116 * <p>
117 * The JSP container will resynchronize the values of any AT_BEGIN and
118 * NESTED variables (defined by the associated TagExtraInfo or TLD) after
119 * the invocation of doAfterBody().
120 *
121 * @return whether additional evaluations of the body are desired
122 * @throws JspException if an error occurred while processing this tag
123 */
124
125 int doAfterBody() throws JspException;
126 }