How can I generate random strings in java?

Question

Possible Duplicate:
How to generate a random alpha-numeric string in Java

I want to write a code that build random string by Specified length . how can do it?

Answer 1

Here are the examples to generate two types of strings.

import java.security.SecureRandom;
import java.math.BigInteger;

public final class SessionIdentifierGenerator
{

  private SecureRandom random = new SecureRandom();

  public String nextSessionId()
  {
    return new BigInteger(130, random).toString(32);
  }

}

OUTPUT: ponhbh78cqjahls5flbdf4dlu4

Refer here

String uuid = UUID.randomUUID().toString();
System.out.println("uuid = " + uuid);

OUTPUT: 281211f4-c1d7-457a-9758-555041a5ff97

Refer here

Answer 2

Well, you first write a function that will give you a random character meeting your requirements, then wrap that up in a for loop based on the desired length.

The following program gives one way of doing this, using a constant pool of characters and a random number generator:

import java.util.Random;

public class testprog {
    private static final char[] pool = {
        'a','b','c','d','e','f','g',
        'h','i','j','k','l','m','n',
        'o','p','q','r','s','t','u',
        'v','w','x','y','z'};

    private Random rnd;

    public testprog () { rnd = new Random(); }

    public char getChar() { return pool[rnd.nextInt(pool.length)]; }

    public String getStr(int sz) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < sz; i++)
            sb.append(getChar());
        return new String(sb);
    }

    public static void main(String[] args) {
        testprog tp = new testprog ();
        for (int i = 0; i < 10; i++)
            System.out.println (tp.getStr(i+5));
    }
}

On one particular run, that gives me:

hgtbf
xismun
cfdnazi
cmpczbal
vhhxwjzbx
gfjxgihqhh
yjgiwnftcnv
ognwcvjucdnm
hxiyqjyfkqenq
jwmncfsrynuwed

Now, you can adjust the pool of characters if you want it from a different character set, you can even adjust the skewing towards specific characters by changing how often they occur in the array (more e characters than z, for example).

But that should be a good start for what you're trying to do.