Generate specific-length hash from a String using Java

Question

I want to hash a String (with variable length) into a fixed-length String (the length can be specified) using Java programming language. The output hash is for unique-detection only, there are no security-requirement here. All characters from the result String should be equal in randomness. Please give me a efficient way to do this (an algorithm, an existing Java method, a library,... are all okay). Thank you!

PS: I want to give some example for clarification:

    String message = "example message";
    // hash(msg, length) is the method I want
    // The output length can be specified in this method
    String hash1 = hash(message, 5); // "s40j7"
    String hash2 = hash(message, 8); // "orpx6klg"