How to find number of JRE present on a computer?

Question

How can i find the jre's present in working computer.
e.g i specified the path as c:/program files/java
it may contain jre1.4.0_14 and jre1.5.0_05
how can i search this and return the version?

Answer 1

A class should be written which can detect the Java Runtime Engines installed on a computer. The search will accept a list of folders as input.
Class 1: JRESearcher class
This method must conduct the search. It must search recursively in each folder supplied for a JRE. For each JRE that is located it must
public class JRESearcher {
     public List<JREResult> search(List<File> folderList)
          //code to do
          - identify the version information
          - create a JREResult object
          - set the fields in the JREResult object
          //end
All the JREResult's are returned as a list.
Class 2 : JREResult class
This class will hold the information on a located JRE. It should be as follows:
public class JREResult
// The location of the JRE. For example, C:\Program Files\Java\jdk1.5.0_14\jre. This is given by System.getProperty("java.home") when running the JRE
public File jrePath;
// e.g. "1.5.0_14". The string returned by "java -version" or given by System.getProperty("java.version") when running the JRE
public String java_version;
// e.g. 1. This is identified by parsing java_version
public int majorVersion;
// e.g. 5. This is identified by parsing java_version
public int minorVersion;
// e.g. 0. This is identified by parsing java_version
public int revision;
// e.g. 14. This is identified by parsing java_version
public int update;
* This method must parse java_version and set majorVersion, minorVersion, revision and update
public void interpretVersionString()
// TODO : code here which interprets java_version
public String toString()
String buf = "JRE " + java_version + " in " + jrePath.getPath() + "\n";
buf += "Major: " + majorVersion + " Minor: " + minorVersion + " Revision: " + revision + " Update: " + update;
return buf;
Class 3: JRESearcherTest class
The following code should be used (in a class called JRESearcherTest) for testing:
public static void main(String[] args)
List<File> folderList = new LinkedList<File>();
     folderList.add(new File("C:/Program Files/Java"));
     folderList.add(new File("C:/Program Files/Javasoft"));
JRESearcher searcher = new JRESearcher();
List<JREResult> jreList = searcher.search(folderList);
for(JREResult result : jreList)
System.out.println(result.toString() + "\n");
To identify the JRE version, do not use the folder name as the basis for the version. Instead the java executable must be interrogated (e.g. "java -version").
The code must be tested in scenarios where all JRE's are present (e.g JRE 1.6, 1.5, 1.4, 1.3, 1.2, 1.1) and with different updates.