Java tutorial
/* * Copyright (c) 1995, 2013, Oracle and/or its affiliates. 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. Oracle designates this * particular file as subject to the "Classpath" exception as provided * by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. */ package java.net; import java.io.IOException; /** * The abstract class {@code ContentHandler} is the superclass * of all classes that read an {@code Object} from a * {@code URLConnection}. * <p> * An application does not generally call the * {@code getContent} method in this class directly. Instead, an * application calls the {@code getContent} method in class * {@code URL} or in {@code URLConnection}. * The application's content handler factory (an instance of a class that * implements the interface {@code ContentHandlerFactory} set up by a call to * {@link URLConnection#setContentHandlerFactory(ContentHandlerFactory) * setContentHandlerFactory} is called with a {@code String} giving the * MIME type of the object being received on the socket. The factory returns an * instance of a subclass of {@code ContentHandler}, and its * {@code getContent} method is called to create the object. * <p> * If no content handler could be {@linkplain URLConnection#getContent() found}, * URLConnection will look for a content handler in a user-definable set of places. * Users can define a vertical-bar delimited set of class prefixes * to search through by defining the <i>{@value java.net.URLConnection#contentPathProp}</i> * property. The class name must be of the form: * <blockquote> * <i>{package-prefix}.{major}.{minor}</i> * <p> * where <i>{major}.{minor}</i> is formed by taking the * content-type string, replacing all slash characters with a * {@code period} ('.'), and all other non-alphanumeric characters * with the underscore character '{@code _}'. The alphanumeric * characters are specifically the 26 uppercase ASCII letters * '{@code A}' through '{@code Z}', the 26 lowercase ASCII * letters '{@code a}' through '{@code z}', and the 10 ASCII * digits '{@code 0}' through '{@code 9}'. * <p> * e.g. * YoyoDyne.experimental.text.plain * </blockquote> * If no user-defined content handler is found, then the system * tries to load a specific <i>content-type</i> handler from one * of the built-in handlers, if one exists. * <p> * 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 1.0 */ public abstract 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}. * @exception IOException if an I/O error occurs while reading the object. */ public abstract 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 * {@link #getContent(URLConnection)} * 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} that is * the first match of the suggested types or * {@code null} if none of the requested are supported. * @exception IOException if an I/O error occurs while reading the object. * @since 1.3 */ @SuppressWarnings("rawtypes") public Object getContent(URLConnection urlc, Class[] classes) throws IOException { Object obj = getContent(urlc); for (Class<?> c : classes) { if (c.isInstance(obj)) { return obj; } } return null; } }