Module com.github.f4b6a3.uuid
Package com.github.f4b6a3.uuid.util.internal

Class RandomUtil

  • public final class RandomUtil
extends Object
    Utility class that provides random generator services.

    The current implementation uses a pool SecureRandom.

    The pool size depends on the number of processors available, up to a maximum of 32. The minimum is 4.

    The pool items are deleted very often to avoid holding them for too long. They are also deleted to avoid holding more instances than threads running.

    The PRNG algorithm can be specified by system property or environment variable. See newSecureRandom().

    • Method Detail

      • nextLong

        public static long nextLong()
        Returns a random 64-bit number.
        Returns:
        a number

      • nextBytes

        public static byte[] nextBytes​(int length)
        Returns an array of random bytes.
        Parameters:
        length - the array length
        Returns:
        a byte array

      • newSecureRandom

        public static SecureRandom newSecureRandom()
        Returns a new instance of SecureRandom.

        It tries to create an instance with the algorithm name specified in the system property `uuidcreator.securerandom` or in the environment variable `UUIDCREATOR_SECURERANDOM`. If the algorithm name is not supported by the runtime, it returns an instance with the default algorithm.

        It can be useful to make use of SHA1PRNG or DRBG as a non-blocking source of random bytes. The SHA1PRNG algorithm is default on operating systems that don't have '/dev/random', e.g., on Windows. The DRBG algorithm is available in JDK 9+.

        To control the algorithm used by this method, use the system property `uuidcreator.securerandom` or the environment variable `UUIDCREATOR_SECURERANDOM` as in examples below.

        System property: 

        
 # Use the the algorithm SHA1PRNG for SecureRandom
 -Duuidcreator.securerandom="SHA1PRNG"
 
 # Use the the algorithm DRBG for SecureRandom (JDK9+)
 -Duuidcreator.securerandom="DRBG"

        Environment variable: 

        
 # Use the the algorithm SHA1PRNG for SecureRandom
 export UUIDCREATOR_SECURERANDOM="SHA1PRNG"
 
 # Use the the algorithm DRBG for SecureRandom (JDK9+)
 export UUIDCREATOR_SECURERANDOM="DRBG"
        Returns:
        a new SecureRandom.