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 package javax.servlet.jsp.tagext;
18
19 import javax.servlet.jsp;
20
21 /**
22 * The BodyTag interface extends IterationTag by defining additional
23 * methods that let a tag handler manipulate the content of evaluating its body.
24 *
25 * <p>
26 * It is the responsibility of the tag handler to manipulate the body
27 * content. For example the tag handler may take the body content,
28 * convert it into a String using the bodyContent.getString
29 * method and then use it. Or the tag handler may take the body
30 * content and write it out into its enclosing JspWriter using
31 * the bodyContent.writeOut method.
32 *
33 * <p> A tag handler that implements BodyTag is treated as one that
34 * implements IterationTag, except that the doStartTag method can
35 * return SKIP_BODY, EVAL_BODY_INCLUDE or EVAL_BODY_BUFFERED.
36 *
37 * <p>
38 * If EVAL_BODY_INCLUDE is returned, then evaluation happens
39 * as in IterationTag.
40 *
41 * <p>
42 * If EVAL_BODY_BUFFERED is returned, then a BodyContent object will be
43 * created (by code generated by the JSP compiler) to capture the body
44 * evaluation.
45 * The code generated by the JSP compiler obtains the BodyContent object by
46 * calling the pushBody method of the current pageContext, which
47 * additionally has the effect of saving the previous out value.
48 * The page compiler returns this object by calling the popBody
49 * method of the PageContext class;
50 * the call also restores the value of out.
51 *
52 * <p>
53 * The interface provides one new property with a setter method and one
54 * new action method.
55 *
56 * <p><B>Properties</B>
57 * <p> There is a new property: bodyContent, to contain the BodyContent
58 * object, where the JSP Page implementation object will place the
59 * evaluation (and reevaluation, if appropriate) of the body. The setter
60 * method (setBodyContent) will only be invoked if doStartTag() returns
61 * EVAL_BODY_BUFFERED and the corresponding action element does not have
62 * an empty body.
63 *
64 * <p><B>Methods</B>
65 * <p> In addition to the setter method for the bodyContent property, there
66 * is a new action method: doInitBody(), which is invoked right after
67 * setBodyContent() and before the body evaluation. This method is only
68 * invoked if doStartTag() returns EVAL_BODY_BUFFERED.
69 *
70 * <p><B>Lifecycle</B>
71 * <p> Lifecycle details are described by the transition diagram below.
72 * Exceptions that are thrown during the computation of doStartTag(),
73 * setBodyContent(), doInitBody(), BODY, doAfterBody() interrupt the
74 * execution sequence and are propagated up the stack, unless the
75 * tag handler implements the TryCatchFinally interface; see that
76 * interface for details.
77 * <p>
78 * <IMG src="doc-files/BodyTagProtocol.gif"
79 * alt="Lifecycle Details Transition Diagram for BodyTag"/>
80 *
81 * <p><B>Empty and Non-Empty Action</B>
82 * <p> If the TagLibraryDescriptor file indicates that the action must
83 * always have an empty element body, by an <body-content> entry
84 * of "empty", then the doStartTag() method must return SKIP_BODY.
85 * Otherwise, the doStartTag() method may return SKIP_BODY,
86 * EVAL_BODY_INCLUDE, or EVAL_BODY_BUFFERED.
87 *
88 * <p>Note that which methods are invoked after the doStartTag() depends on
89 * both the return value and on if the custom action element is empty
90 * or not in the JSP page, not how it's declared in the TLD.
91 *
92 * <p>
93 * If SKIP_BODY is returned the body is not evaluated, and doEndTag() is
94 * invoked.
95 *
96 * <p>
97 * If EVAL_BODY_INCLUDE is returned, and the custom action element is not
98 * empty, setBodyContent() is not invoked,
99 * doInitBody() is not invoked, the body is evaluated and
100 * "passed through" to the current out, doAfterBody() is invoked
101 * and then, after zero or more iterations, doEndTag() is invoked.
102 * If the custom action element is empty, only doStart() and
103 * doEndTag() are invoked.
104 *
105 * <p>
106 * If EVAL_BODY_BUFFERED is returned, and the custom action element is not
107 * empty, setBodyContent() is invoked,
108 * doInitBody() is invoked, the body is evaluated, doAfterBody() is
109 * invoked, and then, after zero or more iterations, doEndTag() is invoked.
110 * If the custom action element is empty, only doStart() and doEndTag()
111 * are invoked.
112 */
113
114 public interface BodyTag extends IterationTag {
115
116 /**
117 * Deprecated constant that has the same value as EVAL_BODY_BUFFERED
118 * and EVAL_BODY_AGAIN. This name has been marked as deprecated
119 * to encourage the use of the two different terms, which are much
120 * more descriptive.
121 *
122 * @deprecated As of Java JSP API 1.2, use BodyTag.EVAL_BODY_BUFFERED
123 * or IterationTag.EVAL_BODY_AGAIN.
124 */
125 @SuppressWarnings("dep-ann") // TCK signature test fails with annotation
126 public final static int EVAL_BODY_TAG = 2;
127
128 /**
129 * Request the creation of new buffer, a BodyContent on which to
130 * evaluate the body of this tag.
131 *
132 * Returned from doStartTag when it implements BodyTag.
133 * This is an illegal return value for doStartTag when the class
134 * does not implement BodyTag.
135 */
136
137 public final static int EVAL_BODY_BUFFERED = 2;
138
139
140 /**
141 * Set the bodyContent property.
142 * This method is invoked by the JSP page implementation object at
143 * most once per action invocation.
144 * This method will be invoked before doInitBody.
145 * This method will not be invoked for empty tags or for non-empty
146 * tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE.
147 *
148 * <p>
149 * When setBodyContent is invoked, the value of the implicit object out
150 * has already been changed in the pageContext object. The BodyContent
151 * object passed will have not data on it but may have been reused
152 * (and cleared) from some previous invocation.
153 *
154 * <p>
155 * The BodyContent object is available and with the appropriate content
156 * until after the invocation of the doEndTag method, at which case it
157 * may be reused.
158 *
159 * @param b the BodyContent
160 * @see #doInitBody
161 * @see #doAfterBody
162 */
163
164 void setBodyContent(BodyContent b);
165
166
167 /**
168 * Prepare for evaluation of the body.
169 * This method is invoked by the JSP page implementation object
170 * after setBodyContent and before the first time
171 * the body is to be evaluated.
172 * This method will not be invoked for empty tags or for non-empty
173 * tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE.
174 *
175 * <p>
176 * The JSP container will resynchronize the values of any AT_BEGIN and
177 * NESTED variables (defined by the associated TagExtraInfo or TLD) after
178 * the invocation of doInitBody().
179 *
180 * @throws JspException if an error occurred while processing this tag
181 * @see #doAfterBody
182 */
183
184 void doInitBody() throws JspException;
185
186 }