ContentHandler


1   /*
2    * @(#)ContentHandler.java  1.20 06/04/07
3    *
4    * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5    * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6    */
7   
8   package java.net;
9   
10  import java.io.IOException  ;
11  
12  /**
13   * The abstract class <code>ContentHandler</code> is the superclass 
14   * of all classes that read an <code>Object</code> from a 
15   * <code>URLConnection</code>. 
16   * <p>
17   * An application does not generally call the 
18   * <code>getContent</code> method in this class directly. Instead, an 
19   * application calls the <code>getContent</code> method in class 
20   * <code>URL</code> or in <code>URLConnection</code>.
21   * The application's content handler factory (an instance of a class that 
22   * implements the interface <code>ContentHandlerFactory</code> set 
23   * up by a call to <code>setContentHandler</code>) is 
24   * called with a <code>String</code> giving the MIME type of the 
25   * object being received on the socket. The factory returns an 
26   * instance of a subclass of <code>ContentHandler</code>, and its 
27   * <code>getContent</code> method is called to create the object. 
28   * <p>
29   * If no content handler could be found, URLConnection will 
30   * look for a content handler in a user-defineable set of places.
31   * By default it looks in sun.net.www.content, but users can define a 
32   * vertical-bar delimited set of class prefixes to search through in 
33   * addition by defining the java.content.handler.pkgs property.
34   * The class name must be of the form:
35   * <pre>
36   *     {package-prefix}.{major}.{minor}
37   * e.g.
38   *     YoyoDyne.experimental.text.plain
39   * </pre>
40   * If the loading of the content handler class would be performed by 
41   * a classloader that is outside of the delegation chain of the caller,
42   * the JVM will need the RuntimePermission "getClassLoader".
43   * 
44   * @author  James Gosling
45   * @version 1.20, 04/07/06
46   * @see     java.net.ContentHandler#getContent(java.net.URLConnection)
47   * @see     java.net.ContentHandlerFactory
48   * @see     java.net.URL#getContent()
49   * @see     java.net.URLConnection
50   * @see     java.net.URLConnection#getContent()
51   * @see     java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
52   * @since   JDK1.0
53   */
54  abstract public class ContentHandler {
55      /** 
56       * Given a URL connect stream positioned at the beginning of the 
57       * representation of an object, this method reads that stream and 
58       * creates an object from it. 
59       *
60       * @param      urlc   a URL connection.
61       * @return     the object read by the <code>ContentHandler</code>.
62       * @exception  IOException  if an I/O error occurs while reading the object.
63       */
64      abstract public Object   getContent(URLConnection   urlc) throws IOException  ;
65  
66      /** 
67       * Given a URL connect stream positioned at the beginning of the 
68       * representation of an object, this method reads that stream and 
69       * creates an object that matches one of the types specified. 
70       *
71       * The default implementation of this method should call getContent()
72       * and screen the return type for a match of the suggested types.
73       *
74       * @param      urlc   a URL connection.
75       * @param      classes  an array of types requested  
76       * @return     the object read by the <code>ContentHandler</code> that is 
77       *                 the first match of the suggested types. 
78       *                 null if none of the requested  are supported.
79       * @exception  IOException  if an I/O error occurs while reading the object.
80       * @since 1.3
81       */
82      public Object   getContent(URLConnection   urlc, Class  [] classes) throws IOException   {
83          Object   obj = getContent(urlc);
84  
85      for (int i = 0; i < classes.length; i++) {
86        if (classes[i].isInstance(obj)) {
87          return obj;
88        }
89      }
90      return null;
91      }
92  
93  }
94
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