Checking the version of JRE used during run-time

问题:

I have multiple version of jre's installed on my system. Is there any way i would know which JRE version is being used by the application during run time.

There might be possible that application may use lower version of JRE -"Not Sure"

Thanks in Advance.

回答1:

Using

System.getProperty("java.version")

will return the version of the currently running JVM.

Sometimes this does not return anything (don't know why). In that case you can try:

System.getProperty("java.runtime.version");

回答2:

Like a_horse_with_no_name said: you can do this by calling System.getProperty("java.version").

If you need this information to make sure that the program is started using the correct JVM version, then try this:

public class Version
{
    //specifies minimum major version. Examples: 5 (JRE 5), 6 (JRE 6), 7 (JRE 7) etc.
    private static final int MAJOR_VERSION = 7;

    //specifies minimum minor version. Examples: 12 (JRE 6u12), 23 (JRE 6u23), 2 (JRE 7u2) etc.
    private static final int MINOR_VERSION = 1;

    //checks if the version of the currently running JVM is bigger than
    //the minimum version required to run this program.
    //returns true if it's ok, false otherwise
    private static boolean isOKJVMVersion()
    {
        //get the JVM version
        String version = System.getProperty("java.version");

        //extract the major version from it
        int sys_major_version = Integer.parseInt(String.valueOf(version.charAt (2)));

        //if the major version is too low (unlikely !!), it's not good
        if (sys_major_version < MAJOR_VERSION) {
            return false;
        } else if (sys_major_version > MAJOR_VERSION) {
            return true;
        } else {
            //find the underline ( "_" ) in the version string
            int underlinepos = version.lastIndexOf("_");

            try {
                //everything after the underline is the minor version.
                //extract that
                int mv = Integer.parseInt(version.substring(underlinepos + 1));

                //if the minor version passes, wonderful
                return (mv >= MINOR_VERSION);

            } catch (NumberFormatException e) {
                //if it's not ok, then the version is probably not good
                return false;
            }
        }
    }

    public static void main(String[] args)
    {
        //check if the minimum version is ok
        if (! isOKJVMVersion()) {
            //display an error message
            //or quit program
            //or... something...
        }
    }
}

All you have to do is change MAJOR_VERSION and MINOR_VERSION to the values that you want and recompile. I use it in my programs all the time and it works well. Warning: it doesn't work if you change System.getProperty("java.version") with System.getProperty("java.runtime.version")... the output is slightly different.

回答3:

You can put this into static code of a class so it runs only once: (This code is not mine. You can refer here:- Getting Java version at runtime

public static double JAVA_VERSION = getVersion ();

public static double getVersion () {
    String version = System.getProperty("java.version");
    int pos = version.indexOf('.');
    pos = version.indexOf('.', pos+1);
    return Double.parseDouble (version.substring (0, pos));
}

---

And if that does not turn up..

String version = Runtime.class.getPackage().getImplementationVersion()

---

Other links you can refer:

http://www.oracle.com/technetwork/java/javase/versioning-naming-139433.html http://docs.oracle.com/javase/1.5.0/docs/relnotes/version-5.0.html