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Java > Open Source Codes > javax > security > auth > callback > CallbackHandler


1 /*
2  * @(#)CallbackHandler.java 1.17 04/06/28
3  *
4  * Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5  * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6  */
7
8 package javax.security.auth.callback;
9
10 /**
11  * <p> An application implements a <code>CallbackHandler</code> and passes
12  * it to underlying security services so that they may interact with
13  * the application to retrieve specific authentication data,
14  * such as usernames and passwords, or to display certain information,
15  * such as error and warning messages.
16  *
17  * <p> CallbackHandlers are implemented in an application-dependent fashion.
18  * For example, implementations for an application with a graphical user
19  * interface (GUI) may pop up windows to prompt for requested information
20  * or to display error messages. An implementation may also choose to obtain
21  * requested information from an alternate source without asking the end user.
22  *
23  * <p> Underlying security services make requests for different types
24  * of information by passing individual Callbacks to the
25  * <code>CallbackHandler</code>. The <code>CallbackHandler</code>
26  * implementation decides how to retrieve and display information
27  * depending on the Callbacks passed to it. For example,
28  * if the underlying service needs a username and password to
29  * authenticate a user, it uses a <code>NameCallback</code> and
30  * <code>PasswordCallback</code>. The <code>CallbackHandler</code>
31  * can then choose to prompt for a username and password serially,
32  * or to prompt for both in a single window.
33  *
34  * <p> A default <code>CallbackHandler</code> class implementation
35  * may be specified in the <i>auth.login.defaultCallbackHandler</i>
36  * security property. The security property can be set
37  * in the Java security properties file located in the file named
38  * &lt;JAVA_HOME&gt;/lib/security/java.security, where &lt;JAVA_HOME&gt;
39  * refers to the directory where the JDK was installed.
40  *
41  * <p> If the security property is set to the fully qualified name of a
42  * <code>CallbackHandler</code> implementation class,
43  * then a <code>LoginContext</code> will load the specified
44  * <code>CallbackHandler</code> and pass it to the underlying LoginModules.
45  * The <code>LoginContext</code> only loads the default handler
46  * if it was not provided one.
47  *
48  * <p> All default handler implementations must provide a public
49  * zero-argument constructor.
50  *
51  * @version 1.17, 06/28/04
52  */
53 public interface CallbackHandler {
54
55     /**
56      * <p> Retrieve or display the information requested in the
57      * provided Callbacks.
58      *
59      * <p> The <code>handle</code> method implementation checks the
60      * instance(s) of the <code>Callback</code> object(s) passed in
61      * to retrieve or display the requested information.
62      * The following example is provided to help demonstrate what an
63      * <code>handle</code> method implementation might look like.
64      * This example code is for guidance only. Many details,
65      * including proper error handling, are left out for simplicity.
66      *
67      * <pre>
68      * public void handle(Callback[] callbacks)
69      * throws IOException, UnsupportedCallbackException {
70      *
71      * for (int i = 0; i < callbacks.length; i++) {
72      * if (callbacks[i] instanceof TextOutputCallback) {
73      *
74      * // display the message according to the specified type
75      * TextOutputCallback toc = (TextOutputCallback)callbacks[i];
76      * switch (toc.getMessageType()) {
77      * case TextOutputCallback.INFORMATION:
78      * System.out.println(toc.getMessage());
79      * break;
80      * case TextOutputCallback.ERROR:
81      * System.out.println("ERROR: " + toc.getMessage());
82      * break;
83      * case TextOutputCallback.WARNING:
84      * System.out.println("WARNING: " + toc.getMessage());
85      * break;
86      * default:
87      * throw new IOException("Unsupported message type: " +
88      * toc.getMessageType());
89      * }
90      *
91      * } else if (callbacks[i] instanceof NameCallback) {
92      *
93      * // prompt the user for a username
94      * NameCallback nc = (NameCallback)callbacks[i];
95      *
96      * // ignore the provided defaultName
97      * System.err.print(nc.getPrompt());
98      * System.err.flush();
99      * nc.setName((new BufferedReader
100      * (new InputStreamReader(System.in))).readLine());
101      *
102      * } else if (callbacks[i] instanceof PasswordCallback) {
103      *
104      * // prompt the user for sensitive information
105      * PasswordCallback pc = (PasswordCallback)callbacks[i];
106      * System.err.print(pc.getPrompt());
107      * System.err.flush();
108      * pc.setPassword(readPassword(System.in));
109      *
110      * } else {
111      * throw new UnsupportedCallbackException
112      * (callbacks[i], "Unrecognized Callback");
113      * }
114      * }
115      * }
116      *
117      * // Reads user password from given input stream.
118      * private char[] readPassword(InputStream in) throws IOException {
119      * // insert code to read a user password from the input stream
120      * }
121      * </pre>
122      *
123      * @param callbacks an array of <code>Callback</code> objects provided
124      * by an underlying security service which contains
125      * the information requested to be retrieved or displayed.
126      *
127      * @exception java.io.IOException if an input or output error occurs. <p>
128      *
129      * @exception UnsupportedCallbackException if the implementation of this
130      * method does not support one or more of the Callbacks
131      * specified in the <code>callbacks</code> parameter.
132      */
133     void handle(Callback JavaDoc[] callbacks)
134     throws java.io.IOException JavaDoc, UnsupportedCallbackException JavaDoc;
135 }
136
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