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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

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 * published by the Free Software Foundation.  Oracle designates this

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 * 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.

 *

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package javax.security.auth.callback;

/**

 * 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

 * 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

 * 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

 * if it was not provided one.

 *

 * <p> All default handler implementations must provide a public

 * zero-argument constructor.

 *

 * @see java.security.Security security properties

 */

public interface CallbackHandler {

    /**

     * <p> Retrieve or display the information requested in the

     * provided Callbacks.

     *

     * to retrieve or display the requested information.

     * The following example is provided to help demonstrate what an

     * 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>

     *

     *          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

     */

    void handle(Callback[] callbacks)

    throws java.io.IOException, UnsupportedCallbackException;

}