jdk/src/share/classes/java/net/ContentHandler.java

/*
 * Copyright 1995-2006 Sun Microsystems, Inc.  All Rights Reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code 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.  Sun designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Sun in the LICENSE file that accompanied this code.
 *
 * This code 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 in the LICENSE file that
 * accompanied this code).
 *
 * 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 USA 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 delegation chain of the caller,
 * the JVM will need the RuntimePermission "getClassLoader".
 *
 * @author  James Gosling
 * @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.
     * @since 1.3
     */
    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;
    }

}