Universally Unique Identifiers (UUIDs) are also known as Globally Unique Identifier(GUID) which are 128-bit numbers and are unique on all local systems they are created on also UUIDs created among other systems. Java UUID class is a part of java.util package. Java UUID class represents an immutable universally unique identifier. UUID is a combination of 8-4-4-4-12 characters.
UUID is made up of hex digits (4 char each) along with 4 “-” symbols which makes its length equal to 36 characters. A UUID can have all bits set to zero which is also known as Nil UUID
Structure of UUID
Structure of UUID Terms
- time_low: low 32-bits of time
- time_mid: middle 16-bits of time
- time_hi_and_version: 4-bit version in the MSB, followed by high 12-bits of the time
- clock_seq_hi_and_res_clock_seq_low: 1-3 bit variant in the most significant bits followed by 13-15 bit clock sequence
- node: 48-bit node ID
Applications of Java UUID
- Used in creating session ID for web applications, this is also used for creating transaction ID
- It extends object class
- Used for creating random file names
- Implements Serializable and Comparable interfaces
- Used to generate primary key for Database Table
Methods to generate Java UUID
Version 1: Generating node() value for time based UUID
Here, the method returns the long value of the node from UUID, and to fetch node value we need to create a time-based (version 1) UUID. It returns the node value associated with the UUID. It is a 48-bit node value. It holds the IEEE 802 address (MAC Address) of the machine.
Example:
Java
// Java program for Generating node()// value for time based UUID//import UUID packageimport java.util.UUID;public class UUIDMain { public static void main(String arg[]) { // returns a UUID with specified value UUID uuid = UUID.fromString("237e9877-e79b-12d4-a765-321741963000"); // returns node value System.out.println("Node value: " + uuid.node()); System.out.println("UUID Version : " + uuid.version()); }} |
Node value: 55075465998336 UUID Version : 1
Version 2: Name based UUID
A Static factory method used to fetch name-based UUID using the specified byte array. It uses “name” in the broadcast sense imaginable and a UUID indicating the type of name used.
Example:
Java
// Java program for generating Name based UUIDimport java.util.UUID;public class Main { public static void main(String[] args) { // initialize byte array byte[] bs = { 1, 2, 3 }; // initialize uuid using byte array UUID uuid = UUID.nameUUIDFromBytes(bs); System.out.println("UUID : " + uuid); System.out.println("UUID Version : " + uuid.version()); }} |
UUID : 5289df73-7df5-3326-bcdd-22597afb1fac UUID Version : 3
UUID for Linux Machine
The above two approaches can be used to generate UUID for the Linux system. To generate a system UUID for Linux Machine there are some pre-requisites needed before generating a UUID.
- Java Development Kit(JDK) should be installed, the latest version would work much better here
- Setting up of Vim or Gedit editor for compiling and running the code is needed.
- Basics of working with Vim editor required to compile, save, run and edit the program.
- Knowledge of running code in both Vim Editor and Linux Kernel/Terminal with the help of Linux commands.
For the code given below, Vim Editor is used to compiling and running the program. UUID is a unique identifier used in partitions to uniquely identify partitions in Linux operating systems. UUID is a property of the disk partition itself.
In the code below, we import the Buffer reader and Input Stream Reader package, then we generate a random UUID with the help of the String method to get the inputs from it and generating UUID.
Java
// Java Program to get System UUID Number for linux Machine// (Root User Login is Req for running the code)import java.io.BufferedReader;import java.io.InputStreamReader;public class Main { // Method for get System UUID for Linux Machine static String getLinuxSystem_UUID() { String command = "dmidecode -s system-uuid"; // setting uuid to null first String uuid = null; try { Process SerNumProcess = Runtime.getRuntime().exec(command); BufferedReader sNumReader = new BufferedReader(new InputStreamReader( SerNumProcess.getInputStream())); // reads the uuid line by line to separate the // uuid into 4 parts uuid = sNumReader.readLine().trim(); SerNumProcess.waitFor(); sNumReader.close(); } catch (Exception ex) { System.err.println("Linux UUID Exp : " + ex.getMessage()); uuid = null; } finally { return uuid; } } public static void main(String[] args) { // generates uuid for linux system String system_uuid = getLinuxSystem_UUID(); System.out.println("Linux System UUID Number : " + system_uuid); }} |
Output:
System UUID for Linux Machine
