Java tutorial
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If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. * * * This file incorporates work covered by the following copyright and * permission notice: * * Copyright 2004 The Apache Software Foundation * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package javax.servlet.jsp.tagext; import javax.servlet.jsp.*; /** * The BodyTag interface extends IterationTag by defining additional * methods that let a tag handler manipulate the content of evaluating its body. * * <p> * It is the responsibility of the tag handler to manipulate the body * content. For example the tag handler may take the body content, * convert it into a String using the bodyContent.getString * method and then use it. Or the tag handler may take the body * content and write it out into its enclosing JspWriter using * the bodyContent.writeOut method. * * <p> A tag handler that implements BodyTag is treated as one that * implements IterationTag, except that the doStartTag method can * return SKIP_BODY, EVAL_BODY_INCLUDE or EVAL_BODY_BUFFERED. * * <p> * If EVAL_BODY_INCLUDE is returned, then evaluation happens * as in IterationTag. * * <p> * If EVAL_BODY_BUFFERED is returned, then a BodyContent object will be * created (by code generated by the JSP compiler) to capture the body * evaluation. * The code generated by the JSP compiler obtains the BodyContent object by * calling the pushBody method of the current pageContext, which * additionally has the effect of saving the previous out value. * The page compiler returns this object by calling the popBody * method of the PageContext class; * the call also restores the value of out. * * <p> * The interface provides one new property with a setter method and one * new action method. * * <p><B>Properties</B> * <p> There is a new property: bodyContent, to contain the BodyContent * object, where the JSP Page implementation object will place the * evaluation (and reevaluation, if appropriate) of the body. The setter * method (setBodyContent) will only be invoked if doStartTag() returns * EVAL_BODY_BUFFERED and the corresponding action element does not have * an empty body. * * <p><B>Methods</B> * <p> In addition to the setter method for the bodyContent property, there * is a new action method: doInitBody(), which is invoked right after * setBodyContent() and before the body evaluation. This method is only * invoked if doStartTag() returns EVAL_BODY_BUFFERED. * * <p><B>Lifecycle</B> * <p> Lifecycle details are described by the transition diagram below. * Exceptions that are thrown during the computation of doStartTag(), * setBodyContent(), doInitBody(), BODY, doAfterBody() interrupt the * execution sequence and are propagated up the stack, unless the * tag handler implements the TryCatchFinally interface; see that * interface for details. * <p> * <IMG src="doc-files/BodyTagProtocol.gif" * alt="Lifecycle Details Transition Diagram for BodyTag"/> * * <p><B>Empty and Non-Empty Action</B> * <p> If the TagLibraryDescriptor file indicates that the action must * always have an empty element body, by an <body-content> entry * of "empty", then the doStartTag() method must return SKIP_BODY. * Otherwise, the doStartTag() method may return SKIP_BODY, * EVAL_BODY_INCLUDE, or EVAL_BODY_BUFFERED. * * <p>Note that which methods are invoked after the doStartTag() depends on * both the return value and on if the custom action element is empty * or not in the JSP page, not how it's declared in the TLD. * * <p> * If SKIP_BODY is returned the body is not evaluated, and doEndTag() is * invoked. * * <p> * If EVAL_BODY_INCLUDE is returned, and the custom action element is not * empty, setBodyContent() is not invoked, * doInitBody() is not invoked, the body is evaluated and * "passed through" to the current out, doAfterBody() is invoked * and then, after zero or more iterations, doEndTag() is invoked. * If the custom action element is empty, only doStart() and * doEndTag() are invoked. * * <p> * If EVAL_BODY_BUFFERED is returned, and the custom action element is not * empty, setBodyContent() is invoked, * doInitBody() is invoked, the body is evaluated, doAfterBody() is * invoked, and then, after zero or more iterations, doEndTag() is invoked. * If the custom action element is empty, only doStart() and doEndTag() * are invoked. */ public interface BodyTag extends IterationTag { /** * Deprecated constant that has the same value as EVAL_BODY_BUFFERED * and EVAL_BODY_AGAIN. This name has been marked as deprecated * to encourage the use of the two different terms, which are much * more descriptive. * * @deprecated As of Java JSP API 1.2, use BodyTag.EVAL_BODY_BUFFERED * or IterationTag.EVAL_BODY_AGAIN. */ public final static int EVAL_BODY_TAG = 2; /** * Request the creation of new buffer, a BodyContent on which to * evaluate the body of this tag. * * Returned from doStartTag when it implements BodyTag. * This is an illegal return value for doStartTag when the class * does not implement BodyTag. */ public final static int EVAL_BODY_BUFFERED = 2; /** * Set the bodyContent property. * This method is invoked by the JSP page implementation object at * most once per action invocation. * This method will be invoked before doInitBody. * This method will not be invoked for empty tags or for non-empty * tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE. * * <p> * When setBodyContent is invoked, the value of the implicit object out * has already been changed in the pageContext object. The BodyContent * object passed will have not data on it but may have been reused * (and cleared) from some previous invocation. * * <p> * The BodyContent object is available and with the appropriate content * until after the invocation of the doEndTag method, at which case it * may be reused. * * @param b the BodyContent * @see #doInitBody * @see #doAfterBody */ void setBodyContent(BodyContent b); /** * Prepare for evaluation of the body. * This method is invoked by the JSP page implementation object * after setBodyContent and before the first time * the body is to be evaluated. * This method will not be invoked for empty tags or for non-empty * tags whose doStartTag() method returns SKIP_BODY or EVAL_BODY_INCLUDE. * * <p> * The JSP container will resynchronize the values of any AT_BEGIN and * NESTED variables (defined by the associated TagExtraInfo or TLD) after * the invocation of doInitBody(). * * @throws JspException if an error occurred while processing this tag * @see #doAfterBody */ void doInitBody() throws JspException; }