001 /* ContentHandler.java -- Abstract class for handling content from URL's 002 Copyright (C) 1998, 1999, 2000, 2001, 2003 Free Software Foundation, Inc. 003 004 This file is part of GNU Classpath. 005 006 GNU Classpath is free software; you can redistribute it and/or modify 007 it under the terms of the GNU General Public License as published by 008 the Free Software Foundation; either version 2, or (at your option) 009 any later version. 010 011 GNU Classpath is distributed in the hope that it will be useful, but 012 WITHOUT ANY WARRANTY; without even the implied warranty of 013 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU 014 General Public License for more details. 015 016 You should have received a copy of the GNU General Public License 017 along with GNU Classpath; see the file COPYING. If not, write to the 018 Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 019 02110-1301 USA. 020 021 Linking this library statically or dynamically with other modules is 022 making a combined work based on this library. Thus, the terms and 023 conditions of the GNU General Public License cover the whole 024 combination. 025 026 As a special exception, the copyright holders of this library give you 027 permission to link this library with independent modules to produce an 028 executable, regardless of the license terms of these independent 029 modules, and to copy and distribute the resulting executable under 030 terms of your choice, provided that you also meet, for each linked 031 independent module, the terms and conditions of the license of that 032 module. An independent module is a module which is not derived from 033 or based on this library. If you modify this library, you may extend 034 this exception to your version of the library, but you are not 035 obligated to do so. If you do not wish to do so, delete this 036 exception statement from your version. */ 037 038 package java.net; 039 040 import java.io.IOException; 041 042 /** 043 * Written using on-line Java Platform 1.2 API Specification, as well 044 * as "The Java Class Libraries", 2nd edition (Addison-Wesley, 1998). 045 * Status: Believed complete and correct. 046 */ 047 048 /** 049 * This is an abstract class that is the superclass for classes that read 050 * objects from URL's. Calling the <code>getContent()</code> method in the 051 * <code>URL</code> class or the <code>URLConnection</code> class will cause 052 * an instance of a subclass of <code>ContentHandler</code> to be created for 053 * the MIME type of the object being downloaded from the URL. Thus, this 054 * class is seldom needed by applications/applets directly, but only 055 * indirectly through methods in other classes. 056 * 057 * @author Aaron M. Renn (arenn@urbanophile.com) 058 * @author Warren Levy (warrenl@cygnus.com) 059 */ 060 public abstract class ContentHandler 061 { 062 /* 063 * Constructors 064 */ 065 066 /** 067 * Default, no-argument constructor. 068 */ 069 public ContentHandler() 070 { 071 } 072 073 /* 074 * Instance Methods 075 */ 076 077 /** 078 * This method reads from the <code>InputStream</code> of the passed in URL 079 * connection and uses the data downloaded to create an <code>Object</code> 080 * represening the content. For example, if the URL is pointing to a GIF 081 * file, this method might return an <code>Image</code> object. This method 082 * must be implemented by subclasses. 083 * 084 * @param urlc A <code>URLConnection</code> object to read data from. 085 * 086 * @return An object representing the data read 087 * 088 * @exception IOException If an error occurs 089 */ 090 public abstract Object getContent(URLConnection urlc) 091 throws IOException; 092 093 /** 094 * This method reads from the <code>InputStream</code> of the passed in URL 095 * connection and uses the data downloaded to create an <code>Object</code> 096 * represening the content. For example, if the URL is pointing to a GIF 097 * file, this method might return an <code>Image</code> object. This method 098 * must be implemented by subclasses. This method uses the list of 099 * supplied classes as candidate types. If the data read doesn't match 100 * any of the supplied type, <code>null</code> is returned. 101 * 102 * @param urlc A <code>URLConnection</code> object to read data from. 103 * @param classes An array of types of objects that are candidate types 104 * for the data to be read. 105 * 106 * @return An object representing the data read, or <code>null</code> 107 * if the data does not match any of the candidate types. 108 * 109 * @exception IOException If an error occurs 110 * 111 * @since 1.3 112 */ 113 public Object getContent(URLConnection urlc, Class[] classes) 114 throws IOException 115 { 116 Object obj = getContent(urlc); 117 118 for (int i = 0; i < classes.length; i++) 119 { 120 if (classes[i].isInstance(obj)) 121 return obj; 122 } 123 124 return null; 125 } 126 } // class ContentHandler