JREVersionDetector

The JREVersionDetector class allows to get the version of a JRE at a specified location, or compare this version with one or two specified version numbers. This class works by trying to start a JVM as an external process with the following command: java -version.

It is also possible to:

• Specify a timeOut for launching the JVM as an external process (the default timeOut is 200 ms)
• Specify a constraint on the JVM architecture (32 bits or 64 bits)

Setting the JRE location

The methods of this class need the location of the JRE as File. The File which is expected is the java.home directory of the JRE to check. The Java executable will be looked for under the <java.home>/bin directory.

Setting the timeOut

The JREVersionDetector.setDefaultTimeOut(long) allow to set the default timeOut for subsequent instances of the class.

The JREVersionDetector.setTimeOut(long) allow to set the timeOut for the current instance of the class.

For example:

   JREVersionDetector detector = new JREVersionDetector();
   // the timeOut will be the default timeOut of 200 ms
   detector.isAtLeastVersion(new File(<my JRE Location>), "1.7");

   JREVersionDetector.setDefaultTimeOut(500L);
   // the timeOut will be the new default timeOut of 500 ms
   detector.isAtLeastVersion(new File(<my JRE Location>), "1.7");

   JREVersionDetector detector2 = new JREVersionDetector();
   detector2.setTimeOut(600L);
   // the timeOut will be 600 ms, the default timeOut has not changed
   detector.isAtLeastVersion(new File(<my JRE Location>), "1.7");

Examples

  JREVersionDetector detector = new JREVersionDetector();
  // return true if the version is at least 1.7
  detector.isAtLeastVersion(new File(<my JRE Location>), "1.7");

  // return true if the version is between 1.7 and 1.8
  detector.isBetweenVersions(new File(<my JRE Location>), "1.7", "1.8", true);

  // return true if the version is between 1.7 and 1.8, and apply a timeOut
  detector.isBetweenVersions(new File(<my JRE Location>), "1.7", "1.8", true);

  // return true if the version is between 1.7 and 1.8, on a 32 bit architecture
  detector.isBetweenVersions(new File(<my JRE Location>), "1.7", "1.8", JREVersionDetector.32_BIT, true);
      
  // get the characteristics of the JRE, will allow to get the version and the architecture
  JREVersionDetector.JREConfig config = detector.getJREConfiguration(new File(<my JRE Location>));