2

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.

Radu Murzea
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Pawan Kumar
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4 Answers4

4

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");
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.

Radu Murzea
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0

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

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Tilak Madichetti
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0

tl;dr

Runtime.version().toString()

See this code run at Ideone.com.

12.0.1+12

Java 9+

The other Answers here are outdated as of Java 9 and Java 10.

Runtime.Version class

Java 9 gained a class dedicated to representing the version of Java: Runtime.Version.

To get an instance of that class, use the version method added to the pre-existing class Runtime.

Runtime.Version v = Runtime.version() ;

From there you interrogate the various pieces of version information.

// Required parts.
int feature = v.feature() ;
int interim = v.interim() ;
int update = v.update() ;
int patch = v.patch() ;

// Optional parts.
Optional<Integer> build = v.build() ;
Optional<String> pre = v.pre() ;
Optional<String> optional = v.optional() ;

See this code run at Ideone.com:

feature: 12
interim: 0
update: 1
patch: 0
build: Optional[12]
pre: Optional.empty
optional: Optional.empty

Note that major, minor, and security are deprecated as of Java 10. Version numbering in Java was redefined in Java 10 and later. To quote the Javadoc:

The sequence may be of arbitrary length but the first four elements are assigned specific meanings, as follows:

$FEATURE.$INTERIM.$UPDATE.$PATCH

$FEATURE — The feature-release counter, incremented for every feature release regardless of release content. Features may be added in a feature release; they may also be removed, if advance notice was given at least one feature release ahead of time. Incompatible changes may be made when justified.

$INTERIM — The interim-release counter, incremented for non-feature releases that contain compatible bug fixes and enhancements but no incompatible changes, no feature removals, and no changes to standard APIs.

$UPDATE — The update-release counter, incremented for compatible update releases that fix security issues, regressions, and bugs in newer features.

$PATCH — The emergency patch-release counter, incremented only when it's necessary to produce an emergency release to fix a critical issue.

The fifth and later elements of a version number are free for use by platform implementors, to identify implementor-specific patch releases.

FYI, Wikipedia maintains a history of Java versions. The Long-Term Support versions are 8, 11, and 17.

Basil Bourque
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