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      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 
     40 import java.security.SecureRandom;
     41 import java.util.ArrayList;
     42 import java.util.List;
     43 import 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  */
     56 public 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