w3hJava

Sometime back, we were discussing something about JRE and one of my friends Lawrence asked me “How to find the number of JRE  installed on system with the help of Java Code ? ”

After giving much thought to it, I don’t think Java has any such API which will tell how many JRE are installed on the System and what are they ? One of my another friend Vikram told me that JRE installation records information in Registry. With this knowledge at the hindsight, I tried to write this piece of code.

It will only run on Windows because I have used Runtime class. I would love to know how the same could be achieved in Unix Systems. This code is not doing anything great, just queries the registry and reflects the answer on the console.

import java.io.*;
class NoofJRE {
    static String REG_PATH = "reg query " +
                          "\"HKLM\Software\JavaSoft\Java Runtime Environment";
       public static void  getJREInfo() {
            try {
            Process process = Runtime.getRuntime().exec(REG_PATH);
                  InputStream inputstream = process.getInputStream();
                  InputStreamReader inputstreamreader = new InputStreamReader(inputstream);
                  BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
                  String line;
                  while ((line = bufferedreader.readLine()) != null) {
                           System.out.println(line);
                  }
          }
            catch (Exception e) {
                  System.out.println("I am in Exception");
        }
      }
      public static void main(String s[]) {
            getJREInfo();
        }
}

And here is my output:

E:\Program Files\Java\jdk1.6.0\bin>java NoofJRE
! REG.EXE VERSION 3.0
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment
CurrentVersion REG_SZ 1.6
BrowserJavaVersion REG_SZ 1.6.0_01
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment\1.4.2_17
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment\1.6
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment\1.6.0
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment\1.6.0_01

Which sounds true in my case. It is clearly telling me that I have JRE 1.4.2_17, 1.6.0 and 1.6.0_01. I have old bad habit of not uninstalling JRE’s :).

Please do let me know if there is any other way to know how many and which JRE is/are installed in my system.

To know where the JRE is installed, one has to do a simple query of JAVA_HOME in the registry.

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