Java password generator

Question

I am trying to create a java program that creates a password, either all lowercase, lowercase and uppercase, lowercase and uppercase and numbers, lowercase and uppercase and numbers and punctuation and the program also has to create one of those password that the user picks and and has to generate a password length according to what the user picks. I have already generated the password options for the user to pick from and have prompted him to pick one. I am now stuck on how to create the password types that were mentioned above. One person suggested me to use ASCII values and then converting them to text. I know how to convert them to text, but it will display number, letters, and punctuations. Is there any way that I can just generate ASCII values for just lowercase letters? Also how will I generate a password according to the user's length that they give?

Answer 1

I use this immutable class.
It uses the builder pattern.
It doesn't support extension.

public final class PasswordGenerator {      private static final String LOWER = "abcdefghijklmnopqrstuvwxyz";     private static final String UPPER = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";     private static final String DIGITS = "0123456789";     private static final String PUNCTUATION = "!@#$%&*()_+-=[]|,./?><";     private boolean useLower;     private boolean useUpper;     private boolean useDigits;     private boolean usePunctuation;      private PasswordGenerator() {         throw new UnsupportedOperationException("Empty constructor is not supported.");     }      private PasswordGenerator(PasswordGeneratorBuilder builder) {         this.useLower = builder.useLower;         this.useUpper = builder.useUpper;         this.useDigits = builder.useDigits;         this.usePunctuation = builder.usePunctuation;     }      public static class PasswordGeneratorBuilder {          private boolean useLower;         private boolean useUpper;         private boolean useDigits;         private boolean usePunctuation;          public PasswordGeneratorBuilder() {             this.useLower = false;             this.useUpper = false;             this.useDigits = false;             this.usePunctuation = false;         }          /**          * Set true in case you would like to include lower characters          * (abc...xyz). Default false.          *          * @param useLower true in case you would like to include lower          * characters (abc...xyz). Default false.          * @return the builder for chaining.          */         public PasswordGeneratorBuilder useLower(boolean useLower) {             this.useLower = useLower;             return this;         }          /**          * Set true in case you would like to include upper characters          * (ABC...XYZ). Default false.          *          * @param useUpper true in case you would like to include upper          * characters (ABC...XYZ). Default false.          * @return the builder for chaining.          */         public PasswordGeneratorBuilder useUpper(boolean useUpper) {             this.useUpper = useUpper;             return this;         }          /**          * Set true in case you would like to include digit characters (123..).          * Default false.          *          * @param useDigits true in case you would like to include digit          * characters (123..). Default false.          * @return the builder for chaining.          */         public PasswordGeneratorBuilder useDigits(boolean useDigits) {             this.useDigits = useDigits;             return this;         }          /**          * Set true in case you would like to include punctuation characters          * (!@#..). Default false.          *          * @param usePunctuation true in case you would like to include          * punctuation characters (!@#..). Default false.          * @return the builder for chaining.          */         public PasswordGeneratorBuilder usePunctuation(boolean usePunctuation) {             this.usePunctuation = usePunctuation;             return this;         }          /**          * Get an object to use.          *          * @return the {@link gr.idrymavmela.business.lib.PasswordGenerator}          * object.          */         public PasswordGenerator build() {             return new PasswordGenerator(this);         }     }      /**      * This method will generate a password depending the use* properties you      * define. It will use the categories with a probability. It is not sure      * that all of the defined categories will be used.      *      * @param length the length of the password you would like to generate.      * @return a password that uses the categories you define when constructing      * the object with a probability.      */     public String generate(int length) {         // Argument Validation.         if (length <= 0) {             return "";         }          // Variables.         StringBuilder password = new StringBuilder(length);         Random random = new Random(System.nanoTime());          // Collect the categories to use.         List<String> charCategories = new ArrayList<>(4);         if (useLower) {             charCategories.add(LOWER);         }         if (useUpper) {             charCategories.add(UPPER);         }         if (useDigits) {             charCategories.add(DIGITS);         }         if (usePunctuation) {             charCategories.add(PUNCTUATION);         }          // Build the password.         for (int i = 0; i < length; i++) {             String charCategory = charCategories.get(random.nextInt(charCategories.size()));             int position = random.nextInt(charCategory.length());             password.append(charCategory.charAt(position));         }         return new String(password);     } } 

This is a usage example,

PasswordGenerator passwordGenerator = new PasswordGenerator.PasswordGeneratorBuilder()         .useDigits(true)         .useLower(true)         .useUpper(true)         .build(); String password = passwordGenerator.generate(8); // output ex.: lrU12fmM 75iwI90o 

Answer 2

You can make use of org.apache.commons.lang.RandomStringUtils to generate random text/passwords. Please refer to this link for example.