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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 java.io.IOException;
27  import java.io.Writer;
28  
29  import javax.servlet.jsp.JspContext;
30  import javax.servlet.jsp.JspException;
31  
32  /**
33   * Encapsulates a portion of JSP code in an object that 
34   * can be invoked as many times as needed.  JSP Fragments are defined 
35   * using JSP syntax as the body of a tag for an invocation to a SimpleTag 
36   * handler, or as the body of a <jsp:attribute> standard action
37   * specifying the value of an attribute that is declared as a fragment,
38   * or to be of type JspFragment in the TLD.
39   * <p>
40   * The definition of the JSP fragment must only contain template 
41   * text and JSP action elements.  In other words, it must not contain
42   * scriptlets or scriptlet expressions.  At translation time, the 
43   * container generates an implementation of the JspFragment abstract class
44   * capable of executing the defined fragment.
45   * <p>
46   * A tag handler can invoke the fragment zero or more times, or 
47   * pass it along to other tags, before returning.  To communicate values
48   * to/from a JSP fragment, tag handlers store/retrieve values in 
49   * the JspContext associated with the fragment.
50   * <p>
51   * Note that tag library developers and page authors should not generate
52   * JspFragment implementations manually.
53   * <p>
54   * <i>Implementation Note</i>: It is not necessary to generate a 
55   * separate class for each fragment.  One possible implementation is 
56   * to generate a single helper class for each page that implements 
57   * JspFragment. Upon construction, a discriminator can be passed to 
58   * select which fragment that instance will execute.
59   *
60   * @since 2.0
61   */
62  public abstract class JspFragment {
63  
64      /**
65       * Executes the fragment and directs all output to the given Writer,
66       * or the JspWriter returned by the getOut() method of the JspContext
67       * associated with the fragment if out is null.
68       *
69       * @param out The Writer to output the fragment to, or null if 
70       *     output should be sent to JspContext.getOut().
71       * @throws javax.servlet.jsp.JspException Thrown if an error occured
72       *     while invoking this fragment.
73       * @throws javax.servlet.jsp.SkipPageException Thrown if the page
74       *     that (either directly or indirectly) invoked the tag handler that
75       *     invoked this fragment is to cease evaluation.  The container
76       *     must throw this exception if a Classic Tag EventHandler returned
77       *     Tag.SKIP_PAGE or if a Simple Tag EventHandler threw SkipPageException.
78       * @throws java.io.IOException If there was an error writing to the 
79       *     stream.
80       */
81      public abstract void invoke( Writer out )
82          throws JspException, IOException;
83  
84      /**
85       * Returns the JspContext that is bound to this JspFragment.
86       *
87       * @return The JspContext used by this fragment at invocation time.
88       */
89      public abstract JspContext getJspContext();
90  
91  }