Java tutorial
/* * Copyright (c) 1999, 2015, 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} 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}. The {@code CallbackHandler} * 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} and * {@code PasswordCallback}. The {@code CallbackHandler} * 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} class implementation * may be specified by setting the value of the * {@code auth.login.defaultCallbackHandler} security property. * * <p> If the security property is set to the fully qualified name of a * {@code CallbackHandler} implementation class, * then a {@code LoginContext} will load the specified * {@code CallbackHandler} and pass it to the underlying LoginModules. * The {@code LoginContext} only loads the default handler * if it was not provided one. * * <p> All default handler implementations must provide a public * zero-argument constructor. * * @since 1.4 * @see java.security.Security security properties */ public interface CallbackHandler { /** * <p> Retrieve or display the information requested in the * provided Callbacks. * * <p> The {@code handle} method implementation checks the * instance(s) of the {@code Callback} object(s) passed in * to retrieve or display the requested information. * The following example is provided to help demonstrate what an * {@code handle} method implementation might look like. * This example code is for guidance only. Many details, * including proper error handling, are left out for simplicity. * * <pre>{@code * 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} 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. * * @exception UnsupportedCallbackException if the implementation of this * method does not support one or more of the Callbacks * specified in the {@code callbacks} parameter. */ void handle(Callback[] callbacks) throws java.io.IOException, UnsupportedCallbackException; }