Get JRE version from application

The JRE installation are listed in the registry in the key only for Windows, Linux do not have central registry.

HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment

You can make a simple program to test :

public class ShowVersion {
 public static void main(String args[]) {
   System.out.println(System.getProperty("java.version"));
 }
}

Or you can try command prompt

Type java -version

For more you can refer sister site of SO :

https://superuser.com/questions/1221096/how-do-i-check-what-version-of-java-i-have-installed

if you're bundling a JRE (did you check the distribution license for it? Make sure you are allowed to do so) and it's running under that, you get that version back.

If the user were to run it under another JRE, you'd get the version of that JRE. That's just how things work.

In fact if you're using a self-contained JRE the user doesn't even have to have another JRE installed on his system at all, that's the entire point of bundling one in the first place.

Apart from a full file system scan it's impossible to know what other JVMs might be installed, and if you do that you'd have to account for all the different names the Java runtime executables may have depending on the files system you're running on. And after finding all those executables you still have no real way of knowing what version of Java they belong to unless you either do a binary analysis of the executables or somehow detect the information from other files in the directories where those executables are installed, files that may or may not be present depending on the system in question, how it was set up, what JVM is in use, and whether the installation has been manually altered or not.

For example, in the root directory of a JDK installation there is a file called "release" which contains the JVM version, but AFAIK that file isn't required to be there for the JVM to work properly. And your application may not have the rights to the file system to read that file.

You can try looking in known paths e.g. C:\Program Files\Java but unless you scan the entire file system for java or java.exe you will never be sure.

This might not work as expected as in the user that runs your application shouldn't have access to system directories. You can force you application to be started with administrator level access but that would be a security risk.

You requirement seems a bit pointless if you are already bundling a JRE with your application.

You can run cmd command using java (java -version) and use that output to get version.

    List<String> cmdArgs = new ArrayList<>();   

                        cmdArgs.add("cmd.exe");
                        cmdArgs.add("/C");
                        cmdArgs.add("java -version");

    ProcessBuilder processBuilderObj = new ProcessBuilder();
                    processBuilderObj.command(cmdArgs);
      Process process = processBuilderObj.start();
 //get inputStream 
                        BufferedReader data = new BufferedReader(new InputStreamReader(process.getInputStream()));
                        String line1;
                        while ((line = data.readLine()) != null){
                            System.out.println(line);
                        }

While System.getProperty("java.version") returns the version of the Java that your app is running on, calling "java -version" as a system command from your Java app will return the version of the default(installed) Java in your system.

Here are the generic steps to find it programmatically:

1. Using ProcessBuilder in Java, execute the system command "java -version". This is certainly platform-independent.
2. Read the output from executed process. The version is usually on the 1st line of the output (smth like java version "1.8.0_191"), so reading the 1st line is enough.
3. Check using regular expression, if the output matches a string containing a java version, you just parse the version and that will be what you are looking for.
4. Otherwise, it means the output is an error message (smth like -bash: java: command not found), and there is no Java installed in your system.

1. control panel
2. java
3. Java tab
4. view you can see exact version of java used and it's location.