contenthandler.java

来自「This is a resource based on j2me embedde」· Java 代码 · 共 113 行

/*
 * @(#)ContentHandler.java	1.20 06/10/10
 *
 * Copyright  1990-2008 Sun Microsystems, Inc. All Rights Reserved.  
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER  
 *   
 * This program is free software; you can redistribute it and/or  
 * modify it under the terms of the GNU General Public License version  
 * 2 only, as published by the Free Software Foundation.   
 *   
 * This program is distributed in the hope that it will be useful, but  
 * WITHOUT ANY WARRANTY; without even the implied warranty of  
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU  
 * General Public License version 2 for more details (a copy is  
 * included at /legal/license.txt).   
 *   
 * You should have received a copy of the GNU General Public License  
 * version 2 along with this work; if not, write to the Free Software  
 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  
 * 02110-1301 USA   
 *   
 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa  
 * Clara, CA 95054 or visit www.sun.com if you need additional  
 * information or have any questions. 
 *
 */

package java.net;

import java.io.IOException;

/**
 * The abstract class <code>ContentHandler</code> is the superclass 
 * of all classes that read an <code>Object</code> from a 
 * <code>URLConnection</code>. 
 * <p>
 * An application does not generally call the 
 * <code>getContent</code> method in this class directly. Instead, an 
 * application calls the <code>getContent</code> method in class 
 * <code>URL</code> or in <code>URLConnection</code>.
 * The application's content handler factory (an instance of a class that 
 * implements the interface <code>ContentHandlerFactory</code> set 
 * up by a call to <code>setContentHandler</code>) is 
 * called with a <code>String</code> giving the MIME type of the 
 * object being received on the socket. The factory returns an 
 * instance of a subclass of <code>ContentHandler</code>, and its 
 * <code>getContent</code> method is called to create the object. 
 * <p>
 * If no content handler could be found, URLConnection will 
 * look for a content handler in a user-defineable set of places.
 * By default it looks in sun.net.www.content, but users can define a 
 * vertical-bar delimited set of class prefixes to search through in 
 * addition by defining the java.content.handler.pkgs property.
 * The class name must be of the form:
 * <pre>
 *     {package-prefix}.{major}.{minor}
 * e.g.
 *     YoyoDyne.experimental.text.plain
 * </pre>
 * If the loading of the content handler class would be performed by 
 * a classloader that is outside of the the delegation chain of the caller,
 * the JVM will need the RuntimePermission "getClassLoader".
 * 
 * @author  James Gosling
 * @version 1.14, 02/02/00
 * @see     java.net.ContentHandler#getContent(java.net.URLConnection)
 * @see     java.net.ContentHandlerFactory
 * @see     java.net.URL#getContent()
 * @see     java.net.URLConnection
 * @see     java.net.URLConnection#getContent()
 * @see     java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
 * @since   JDK1.0
 */
abstract public class ContentHandler {
    /** 
     * Given a URL connect stream positioned at the beginning of the 
     * representation of an object, this method reads that stream and 
     * creates an object from it. 
     *
     * @param      urlc   a URL connection.
     * @return     the object read by the <code>ContentHandler</code>.
     * @exception  IOException  if an I/O error occurs while reading the object.
     */
    abstract public Object getContent(URLConnection urlc) throws IOException;

    /** 
     * Given a URL connect stream positioned at the beginning of the 
     * representation of an object, this method reads that stream and 
     * creates an object that matches one of the types specified. 
     *
     * The default implementation of this method should call getContent()
     * and screen the return type for a match of the suggested types.
     *
     * @param      urlc   a URL connection.
     * @param      classes	an array of types requested  
     * @return     the object read by the <code>ContentHandler</code> that is 
     *                 the first match of the suggested types. 
     *                 null if none of the requested  are supported.
     * @exception  IOException  if an I/O error occurs while reading the object.
     */
    public Object getContent(URLConnection urlc, Class[] classes) throws IOException {
        Object obj = getContent(urlc);

	for (int i = 0; i < classes.length; i++) {
	  if (classes[i].isInstance(obj)) {
		return obj;
	  }
	}
	return null;
    }

}