How to generate a random string of 20 characters

Question

Possible Duplicate    How to generate a random String in Java       I am wanting to generate a random string of 20 characters without using apache classes  I don t really care about whether is alphanumeric or not  Also  I am going to convert it to an array of bytes later FYI   Thanks

User · Accepted Answer

Here you go  Just specify the chars you want to allow on the first line   char   chars    abcdefghijklmnopqrstuvwxyz  toCharArray    StringBuilder sb   new StringBuilder 20   Random random   new Random    for  int i   0  i  lt  20  i          char c   chars random nextInt chars length        sb append c     String output   sb toString    System out println output          If you are using this to generate something sensitive like a password   reset URL or session ID cookie or temporary password reset  be sure to use   java security SecureRandom instead    Values produced by java util Random and java util concurrent ThreadLocalRandom are mathematically predictable

User · Answer

I d use this approach   String randomString final int length        Random r   new Random       perhaps make it a class variable so you don t make a new one every time     StringBuilder sb   new StringBuilder        for int i   0  i  lt  length  i              char c    char  r nextInt  int  Character MAX VALUE             sb append c             return sb toString        If you want a byte   you can do this   byte   randomByteString final int length        Random r   new Random        byte   result   new byte length       for int i   0  i  lt  length  i              result i    r nextByte              return result      Or you could do this  byte   randomByteString final int length        Random r   new Random        StringBuilder sb   new StringBuilder        for int i   0  i  lt  length  i              char c    char  r nextInt  int  Character MAX VALUE             sb append c             return sb toString   getBytes

User · Answer

You may use the class java util Random with method   char c    char  rnd nextInt 128-32   32    20x to get Bytes  which you interpret as ASCII  If you re fine with ASCII    32 is the offset  from where the characters are printable in general

User · Answer

public String randomString String chars  int length      Random rand   new Random      StringBuilder buf   new StringBuilder      for  int i 0  i lt length  i          buf append chars charAt rand nextInt chars length             return buf toString

[java] How to generate a random string of 20 characters

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