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 }