/* * Copyright (c) 1999, 2005, 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 javax.security.auth.callback; /** * <p> An application implements a <code>CallbackHandler</code> and passes * it to underlying security services so that they may interact with * the application to retrieve specific authentication data, * such as usernames and passwords, or to display certain information, * such as error and warning messages. * * <p> CallbackHandlers are implemented in an application-dependent fashion. * For example, implementations for an application with a graphical user * interface (GUI) may pop up windows to prompt for requested information * or to display error messages.  An implementation may also choose to obtain * requested information from an alternate source without asking the end user. * * <p> Underlying security services make requests for different types * of information by passing individual Callbacks to the * <code>CallbackHandler</code>.  The <code>CallbackHandler</code> * implementation decides how to retrieve and display information * depending on the Callbacks passed to it.  For example, * if the underlying service needs a username and password to * authenticate a user, it uses a <code>NameCallback</code> and * <code>PasswordCallback</code>.  The <code>CallbackHandler</code> * can then choose to prompt for a username and password serially, * or to prompt for both in a single window. * * <p> A default <code>CallbackHandler</code> class implementation * may be specified in the <i>auth.login.defaultCallbackHandler</i> * security property.  The security property can be set * in the Java security properties file located in the file named * &lt;JAVA_HOME&gt;/lib/security/java.security. * &lt;JAVA_HOME&gt; refers to the value of the java.home system property, * and specifies the directory where the JRE is installed. * * <p> If the security property is set to the fully qualified name of a * <code>CallbackHandler</code> implementation class, * then a <code>LoginContext</code> will load the specified * <code>CallbackHandler</code> and pass it to the underlying LoginModules. * The <code>LoginContext</code> only loads the default handler * if it was not provided one. * * <p> All default handler implementations must provide a public * zero-argument constructor. * */public interface CallbackHandler {     /**     * <p> Retrieve or display the information requested in the     * provided Callbacks.     *     * <p> The <code>handle</code> method implementation checks the     * instance(s) of the <code>Callback</code> object(s) passed in     * to retrieve or display the requested information.     * The following example is provided to help demonstrate what an     * <code>handle</code> method implementation might look like.     * This example code is for guidance only.  Many details,     * including proper error handling, are left out for simplicity.     *     * <pre>     * public void handle(Callback[] callbacks)     * throws IOException, UnsupportedCallbackException {     *     *   for (int i = 0; i < callbacks.length; i++) {     *      if (callbacks[i] instanceof TextOutputCallback) {     *     *          // display the message according to the specified type     *          TextOutputCallback toc = (TextOutputCallback)callbacks[i];     *          switch (toc.getMessageType()) {     *          case TextOutputCallback.INFORMATION:     *              System.out.println(toc.getMessage());     *              break;     *          case TextOutputCallback.ERROR:     *              System.out.println("ERROR: " + toc.getMessage());     *              break;     *          case TextOutputCallback.WARNING:     *              System.out.println("WARNING: " + toc.getMessage());     *              break;     *          default:     *              throw new IOException("Unsupported message type: " +     *                                  toc.getMessageType());     *          }     *     *      } else if (callbacks[i] instanceof NameCallback) {     *     *          // prompt the user for a username     *          NameCallback nc = (NameCallback)callbacks[i];     *     *          // ignore the provided defaultName     *          System.err.print(nc.getPrompt());     *          System.err.flush();     *          nc.setName((new BufferedReader     *                  (new InputStreamReader(System.in))).readLine());     *     *      } else if (callbacks[i] instanceof PasswordCallback) {     *     *          // prompt the user for sensitive information     *          PasswordCallback pc = (PasswordCallback)callbacks[i];     *          System.err.print(pc.getPrompt());     *          System.err.flush();     *          pc.setPassword(readPassword(System.in));     *     *      } else {     *          throw new UnsupportedCallbackException     *                  (callbacks[i], "Unrecognized Callback");     *      }     *   }     * }     *     * // Reads user password from given input stream.     * private char[] readPassword(InputStream in) throws IOException {     *    // insert code to read a user password from the input stream     * }     * </pre>     *     * @param callbacks an array of <code>Callback</code> objects provided     *          by an underlying security service which contains     *          the information requested to be retrieved or displayed.     *     * @exception java.io.IOException if an input or output error occurs. <p>     *     * @exception UnsupportedCallbackException if the implementation of this     *          method does not support one or more of the Callbacks     *          specified in the <code>callbacks</code> parameter.     */    void handle(Callback[] callbacks)    throws java.io.IOException, UnsupportedCallbackException;}