1/*
2 * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
3 *
4 * Redistribution and use in source and binary forms, with or without
5 * modification, are permitted provided that the following conditions
6 * are met:
7 *
8 *   - Redistributions of source code must retain the above copyright
9 *     notice, this list of conditions and the following disclaimer.
10 *
11 *   - Redistributions in binary form must reproduce the above copyright
12 *     notice, this list of conditions and the following disclaimer in the
13 *     documentation and/or other materials provided with the distribution.
14 *
15 *   - Neither the name of Oracle nor the names of its
16 *     contributors may be used to endorse or promote products derived
17 *     from this software without specific prior written permission.
18 *
19 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
20 * IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
21 * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
22 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR
23 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
24 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
25 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
26 * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF
27 * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
28 * NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
29 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
30 */
31
32/*
33 * This source code is provided to illustrate the usage of a given feature
34 * or technique and has been deliberately simplified. Additional steps
35 * required for a production-quality application, such as security checks,
36 * input validation, and proper error handling, might not be present in
37 * this sample code.
38 */
39
40import java.security.SecureRandom;
41import java.util.ArrayList;
42import java.util.List;
43import java.util.stream.IntStream;
44
45/**
46 * Generates password of desired length. See {@link #usage} method
47 * for instructions and command line parameters. This sample shows usages of:
48 * <ul>
49 * <li>Method references.</li>
50 * <li>Lambda and bulk operations. A stream of random integers is mapped to
51 * chars, limited by desired length and printed in standard output as password
52 * string.</li>
53 * </ul>
54 *
55 */
56public class PasswordGenerator {
57
58    private static void usage() {
59        System.out.println("Usage: PasswordGenerator LENGTH");
60        System.out.println(
61                "Password Generator produces password of desired LENGTH.");
62    }
63
64    private static final List<Integer> PASSWORD_CHARS = new ArrayList<>();
65
66    //Valid symbols.
67    static {
68        IntStream.rangeClosed('0', '9').forEach(PASSWORD_CHARS::add);    // 0-9
69        IntStream.rangeClosed('A', 'Z').forEach(PASSWORD_CHARS::add);    // A-Z
70        IntStream.rangeClosed('a', 'z').forEach(PASSWORD_CHARS::add);    // a-z
71    }
72
73    /**
74     * The main method for the PasswordGenerator program. Run program with empty
75     * argument list to see possible arguments.
76     *
77     * @param args the argument list for PasswordGenerator.
78     */
79    public static void main(String[] args) {
80
81        if (args.length != 1) {
82            usage();
83            return;
84        }
85
86        long passwordLength;
87        try {
88            passwordLength = Long.parseLong(args[0]);
89            if (passwordLength < 1) {
90                printMessageAndUsage("Length has to be positive");
91                return;
92            }
93        } catch (NumberFormatException ex) {
94            printMessageAndUsage("Unexpected number format" + args[0]);
95            return;
96        }
97        /*
98         * Stream of random integers is created containing Integer values
99         * in range from 0 to PASSWORD_CHARS.size().
100         * The stream is limited by passwordLength.
101         * Valid chars are selected by generated index.
102         */
103        new SecureRandom().ints(passwordLength, 0, PASSWORD_CHARS.size())
104                .map(PASSWORD_CHARS::get)
105                .forEach(i -> System.out.print((char) i));
106    }
107
108    private static void printMessageAndUsage(String message) {
109        System.err.println(message);
110        usage();
111    }
112
113}
114