001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *  http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing,
013     * software distributed under the License is distributed on an
014     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015     * KIND, either express or implied.  See the License for the
016     * specific language governing permissions and limitations
017     * under the License.
018     */
019    
020    //
021    // This source code implements specifications defined by the Java
022    // Community Process. In order to remain compliant with the specification
023    // DO NOT add / change / or delete method signatures!
024    //
025    
026    package javax.servlet.jsp.tagext;
027    
028    import java.io.IOException;
029    import java.io.Writer;
030    import javax.servlet.jsp.*;
031    
032    /**
033     * Encapsulates a portion of JSP code in an object that 
034     * can be invoked as many times as needed.  JSP Fragments are defined 
035     * using JSP syntax as the body of a tag for an invocation to a SimpleTag 
036     * handler, or as the body of a <jsp:attribute> standard action
037     * specifying the value of an attribute that is declared as a fragment,
038     * or to be of type JspFragment in the TLD.
039     * <p>
040     * The definition of the JSP fragment must only contain template 
041     * text and JSP action elements.  In other words, it must not contain
042     * scriptlets or scriptlet expressions.  At translation time, the 
043     * container generates an implementation of the JspFragment abstract class
044     * capable of executing the defined fragment.
045     * <p>
046     * A tag handler can invoke the fragment zero or more times, or 
047     * pass it along to other tags, before returning.  To communicate values
048     * to/from a JSP fragment, tag handlers store/retrieve values in 
049     * the JspContext associated with the fragment.
050     * <p>
051     * Note that tag library developers and page authors should not generate
052     * JspFragment implementations manually.
053     * <p>
054     * <i>Implementation Note</i>: It is not necessary to generate a 
055     * separate class for each fragment.  One possible implementation is 
056     * to generate a single helper class for each page that implements 
057     * JspFragment. Upon construction, a discriminator can be passed to 
058     * select which fragment that instance will execute.
059     *
060     * @since 2.0
061     */
062    public abstract class JspFragment {
063    
064        /**
065         * Executes the fragment and directs all output to the given Writer,
066         * or the JspWriter returned by the getOut() method of the JspContext
067         * associated with the fragment if out is null.
068         *
069         * @param out The Writer to output the fragment to, or null if 
070         *     output should be sent to JspContext.getOut().
071         * @throws javax.servlet.jsp.JspException Thrown if an error occured
072         *     while invoking this fragment.
073         * @throws javax.servlet.jsp.SkipPageException Thrown if the page
074         *     that (either directly or indirectly) invoked the tag handler that
075         *     invoked this fragment is to cease evaluation.  The container
076         *     must throw this exception if a Classic Tag Handler returned
077         *     Tag.SKIP_PAGE or if a Simple Tag Handler threw SkipPageException.
078         * @throws java.io.IOException If there was an error writing to the 
079         *     stream.
080         */
081        public abstract void invoke( Writer out )
082            throws JspException, IOException;
083    
084        /**
085         * Returns the JspContext that is bound to this JspFragment.
086         *
087         * @return The JspContext used by this fragment at invocation time.
088         */
089        public abstract JspContext getJspContext();
090    
091    }