alvinalexander.com | career | drupal | java | mac | mysql | perl | scala | uml | unix  

Jetty example source code file (Tag.java)

This example Jetty source code file (Tag.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Jetty tags/keywords

eval_body_include, eval_body_include, eval_page, eval_page, http, jspexception, jspexception, jsptag, servlet, skip_body, skip_page, tag, tag

The Jetty Tag.java source code

/**
 *
 * Copyright 2003-2004 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.
 */

//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//

package javax.servlet.jsp.tagext;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;


/**
 * The interface of a classic tag handler that does not want to manipulate 
 * its body.  The Tag interface defines the basic protocol between a Tag 
 * handler and JSP page implementation class.  It defines the life cycle 
 * and the methods to be invoked at start and end tag.
 *
 * <p>Properties

* * <p>The Tag interface specifies the setter and getter methods for the core * pageContext and parent properties.</p> * * <p>The JSP page implementation object invokes setPageContext and * setParent, in that order, before invoking doStartTag() or doEndTag().</p> * * <p>Methods

* * <p>There are two main actions: doStartTag and doEndTag. Once all * appropriate properties have been initialized, the doStartTag and * doEndTag methods can be invoked on the tag handler. Between these * invocations, the tag handler is assumed to hold a state that must * be preserved. After the doEndTag invocation, the tag handler is * available for further invocations (and it is expected to have * retained its properties).</p> * * <p>Lifecycle

* * <p>Lifecycle details are described by the transition diagram below, * with the following comments: * <ul> * <li> [1] This transition is intended to be for releasing long-term data. * no guarantees are assumed on whether any properties have been retained * or not. * <li> [2] This transition happens if and only if the tag ends normally * without raising an exception * <li> [3] Some setters may be called again before a tag handler is * reused. For instance, <code>setParent() is called if it's * reused within the same page but at a different level, * <code>setPageContext() is called if it's used in another page, * and attribute setters are called if the values differ or are expressed * as request-time attribute values. * <li> Check the TryCatchFinally interface for additional details related * to exception handling and resource management. * </ul>

* * <IMG src="doc-files/TagProtocol.gif" * alt="Lifecycle Details Transition Diagram for Tag"/> * * <p>Once all invocations on the tag handler * are completed, the release method is invoked on it. Once a release * method is invoked <em>all properties, including parent and * pageContext, are assumed to have been reset to an unspecified value. * The page compiler guarantees that release() will be invoked on the Tag * handler before the handler is released to the GC.</p> * * <p>Empty and Non-Empty Action

* <p>If the TagLibraryDescriptor file indicates that the action must * always have an empty action, by an <body-_content> entry of "empty", * then the doStartTag() method must return SKIP_BODY.</p> * * <p>Otherwise, the doStartTag() method may return SKIP_BODY or * EVAL_BODY_INCLUDE.</p> * * <p>If SKIP_BODY is returned the body, if present, is not evaluated.

* * <p>If EVAL_BODY_INCLUDE is returned, the body is evaluated and * "passed through" to the current out.</p> */ public interface Tag extends JspTag { /** * Skip body evaluation. * Valid return value for doStartTag and doAfterBody. */ public final static int SKIP_BODY = 0; /** * Evaluate body into existing out stream. * Valid return value for doStartTag. */ public final static int EVAL_BODY_INCLUDE = 1; /** * Skip the rest of the page. * Valid return value for doEndTag. */ public final static int SKIP_PAGE = 5; /** * Continue evaluating the page. * Valid return value for doEndTag(). */ public final static int EVAL_PAGE = 6; // Setters for Tag handler data /** * Set the current page context. * This method is invoked by the JSP page implementation object * prior to doStartTag(). * <p> * This value is *not* reset by doEndTag() and must be explicitly reset * by a page implementation if it changes between calls to doStartTag(). * * @param pc The page context for this tag handler. */ void setPageContext(PageContext pc); /** * Set the parent (closest enclosing tag handler) of this tag handler. * Invoked by the JSP page implementation object prior to doStartTag(). * <p> * This value is *not* reset by doEndTag() and must be explicitly reset * by a page implementation. * * @param t The parent tag, or null. */ void setParent(Tag t); /** * Get the parent (closest enclosing tag handler) for this tag handler. * * <p> * The getParent() method can be used to navigate the nested tag * handler structure at runtime for cooperation among custom actions; * for example, the findAncestorWithClass() method in TagSupport * provides a convenient way of doing this. * * <p> * The current version of the specification only provides one formal * way of indicating the observable type of a tag handler: its * tag handler implementation class, described in the tag-class * subelement of the tag element. This is extended in an * informal manner by allowing the tag library author to * indicate in the description subelement an observable type. * The type should be a subtype of the tag handler implementation * class or void. * This addititional constraint can be exploited by a * specialized container that knows about that specific tag library, * as in the case of the JSP standard tag library. * * @return the current parent, or null if none. * @see TagSupport#findAncestorWithClass */ Tag getParent(); // Actions for basic start/end processing. /** * Process the start tag for this instance. * This method is invoked by the JSP page implementation object. * * <p> * The doStartTag method assumes that the properties pageContext and * parent have been set. It also assumes that any properties exposed as * attributes have been set too. When this method is invoked, the body * has not yet been evaluated. * * <p> * This method returns Tag.EVAL_BODY_INCLUDE or * BodyTag.EVAL_BODY_BUFFERED to indicate * that the body of the action should be evaluated or SKIP_BODY to * indicate otherwise. * * <p> * When a Tag returns EVAL_BODY_INCLUDE the result of evaluating * the body (if any) is included into the current "out" JspWriter as it * happens and then doEndTag() is invoked. * * <p> * BodyTag.EVAL_BODY_BUFFERED is only valid if the tag handler * implements BodyTag. * * <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 doStartTag(), except for a tag handler * implementing BodyTag whose doStartTag() method returns * BodyTag.EVAL_BODY_BUFFERED. * * @return EVAL_BODY_INCLUDE if the tag wants to process body, SKIP_BODY * if it does not want to process it. * @throws JspException if an error occurred while processing this tag * @see BodyTag */ int doStartTag() throws JspException; /** * Process the end tag for this instance. * This method is invoked by the JSP page implementation object * on all Tag handlers. * * <p> * This method will be called after returning from doStartTag. The * body of the action may or may not have been evaluated, depending on * the return value of doStartTag. * * <p> * If this method returns EVAL_PAGE, the rest of the page continues * to be evaluated. If this method returns SKIP_PAGE, the rest of * the page is not evaluated, the request is completed, and * the doEndTag() methods of enclosing tags are not invoked. If this * request was forwarded or included from another page (or Servlet), * only the current page evaluation is stopped. * * <p> * The JSP container will resynchronize the values of any AT_BEGIN and * AT_END variables (defined by the associated TagExtraInfo or TLD) * after the invocation of doEndTag(). * * @return indication of whether to continue evaluating the JSP page. * @throws JspException if an error occurred while processing this tag */ int doEndTag() throws JspException; /** * Called on a Tag handler to release state. * The page compiler guarantees that JSP page implementation * objects will invoke this method on all tag handlers, * but there may be multiple invocations on doStartTag and doEndTag in between. */ void release(); }

Other Jetty examples (source code examples)

Here is a short list of links related to this Jetty Tag.java source code file:

... this post is sponsored by my books ...

#1 New Release!

FP Best Seller

 

new blog posts

 

Copyright 1998-2021 Alvin Alexander, alvinalexander.com
All Rights Reserved.

A percentage of advertising revenue from
pages under the /java/jwarehouse URI on this website is
paid back to open source projects.