001 /* 002 * Licensed to the Apache Software Foundation (ASF) under one or more 003 * contributor license agreements. See the NOTICE file distributed with 004 * this work for additional information regarding copyright ownership. 005 * The ASF licenses this file to You under the Apache License, Version 2.0 006 * (the "License"); you may not use this file except in compliance with 007 * the License. You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 package javax.servlet.jsp.tagext; 018 019 import javax.servlet.jsp.*; 020 021 /** 022 * The BodyTag interface extends IterationTag by defining additional 023 * methods that let a tag handler manipulate the content of evaluating its body. 024 * 025 * <p> 026 * It is the responsibility of the tag handler to manipulate the body 027 * content. For example the tag handler may take the body content, 028 * convert it into a String using the bodyContent.getString 029 * method and then use it. Or the tag handler may take the body 030 * content and write it out into its enclosing JspWriter using 031 * the bodyContent.writeOut method. 032 * 033 * <p> A tag handler that implements BodyTag is treated as one that 034 * implements IterationTag, except that the doStartTag method can 035 * return SKIP_BODY, EVAL_BODY_INCLUDE or EVAL_BODY_BUFFERED. 036 * 037 * <p> 038 * If EVAL_BODY_INCLUDE is returned, then evaluation happens 039 * as in IterationTag. 040 * 041 * <p> 042 * If EVAL_BODY_BUFFERED is returned, then a BodyContent object will be 043 * created (by code generated by the JSP compiler) to capture the body 044 * evaluation. 045 * The code generated by the JSP compiler obtains the BodyContent object by 046 * calling the pushBody method of the current pageContext, which 047 * additionally has the effect of saving the previous out value. 048 * The page compiler returns this object by calling the popBody 049 * method of the PageContext class; 050 * the call also restores the value of out. 051 * 052 * <p> 053 * The interface provides one new property with a setter method and one 054 * new action method. 055 * 056 * <p><B>Properties</B> 057 * <p> There is a new property: bodyContent, to contain the BodyContent 058 * object, where the JSP Page implementation object will place the 059 * evaluation (and reevaluation, if appropriate) of the body. The setter 060 * method (setBodyContent) will only be invoked if doStartTag() returns 061 * EVAL_BODY_BUFFERED and the corresponding action element does not have 062 * an empty body. 063 * 064 * <p><B>Methods</B> 065 * <p> In addition to the setter method for the bodyContent property, there 066 * is a new action method: doInitBody(), which is invoked right after 067 * setBodyContent() and before the body evaluation. This method is only 068 * invoked if doStartTag() returns EVAL_BODY_BUFFERED. 069 * 070 * <p><B>Lifecycle</B> 071 * <p> Lifecycle details are described by the transition diagram below. 072 * Exceptions that are thrown during the computation of doStartTag(), 073 * setBodyContent(), doInitBody(), BODY, doAfterBody() interrupt the 074 * execution sequence and are propagated up the stack, unless the 075 * tag handler implements the TryCatchFinally interface; see that 076 * interface for details. 077 * <p> 078 * <IMG src="doc-files/BodyTagProtocol.gif" 079 * alt="Lifecycle Details Transition Diagram for BodyTag"/> 080 * 081 * <p><B>Empty and Non-Empty Action</B> 082 * <p> If the TagLibraryDescriptor file indicates that the action must 083 * always have an empty element body, by an <body-content> entry 084 * of "empty", then the doStartTag() method must return SKIP_BODY. 085 * Otherwise, the doStartTag() method may return SKIP_BODY, 086 * EVAL_BODY_INCLUDE, or EVAL_BODY_BUFFERED. 087 * 088 * <p>Note that which methods are invoked after the doStartTag() depends on 089 * both the return value and on if the custom action element is empty 090 * or not in the JSP page, not how it's declared in the TLD. 091 * 092 * <p> 093 * If SKIP_BODY is returned the body is not evaluated, and doEndTag() is 094 * invoked. 095 * 096 * <p> 097 * If EVAL_BODY_INCLUDE is returned, and the custom action element is not 098 * empty, setBodyContent() is not invoked, 099 * 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 */ 125 126 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 }