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     
018    package javax.servlet.jsp.tagext;
019    
020    import java.io.IOException;
021    import java.io.Writer;
022    import javax.servlet.jsp.*;
023    
024    /**
025     * Encapsulates a portion of JSP code in an object that 
026     * can be invoked as many times as needed.  JSP Fragments are defined 
027     * using JSP syntax as the body of a tag for an invocation to a SimpleTag 
028     * handler, or as the body of a <jsp:attribute> standard action
029     * specifying the value of an attribute that is declared as a fragment,
030     * or to be of type JspFragment in the TLD.
031     * <p>
032     * The definition of the JSP fragment must only contain template 
033     * text and JSP action elements.  In other words, it must not contain
034     * scriptlets or scriptlet expressions.  At translation time, the 
035     * container generates an implementation of the JspFragment abstract class
036     * capable of executing the defined fragment.
037     * <p>
038     * A tag handler can invoke the fragment zero or more times, or 
039     * pass it along to other tags, before returning.  To communicate values
040     * to/from a JSP fragment, tag handlers store/retrieve values in 
041     * the JspContext associated with the fragment.
042     * <p>
043     * Note that tag library developers and page authors should not generate
044     * JspFragment implementations manually.
045     * <p>
046     * <i>Implementation Note</i>: It is not necessary to generate a 
047     * separate class for each fragment.  One possible implementation is 
048     * to generate a single helper class for each page that implements 
049     * JspFragment. Upon construction, a discriminator can be passed to 
050     * select which fragment that instance will execute.
051     *
052     * @since 2.0
053     */
054    public abstract class JspFragment {
055    
056        /**
057         * Executes the fragment and directs all output to the given Writer,
058         * or the JspWriter returned by the getOut() method of the JspContext
059         * associated with the fragment if out is null.
060         *
061         * @param out The Writer to output the fragment to, or null if 
062         *     output should be sent to JspContext.getOut().
063         * @throws javax.servlet.jsp.JspException Thrown if an error occured
064         *     while invoking this fragment.
065         * @throws javax.servlet.jsp.SkipPageException Thrown if the page
066         *     that (either directly or indirectly) invoked the tag handler that
067         *     invoked this fragment is to cease evaluation.  The container
068         *     must throw this exception if a Classic Tag Handler returned
069         *     Tag.SKIP_PAGE or if a Simple Tag Handler threw SkipPageException.
070         * @throws java.io.IOException If there was an error writing to the 
071         *     stream.
072         */
073        public abstract void invoke( Writer out )
074            throws JspException, IOException;
075    
076        /**
077         * Returns the JspContext that is bound to this JspFragment.
078         *
079         * @return The JspContext used by this fragment at invocation time.
080         */
081        public abstract JspContext getJspContext();
082    
083    }