I recently encountered a very similar situation. The following code does almost what you need. He is looking for java JRE and JDK, not just JDK, but they are quite easy to edit to suit your needs. Beware: windows only
/** * Java Finder by petrucio@stackoverflow(828681) is licensed under a Creative Commons Attribution 3.0 Unported License. * Needs WinRegistry.java. Get it at: https://stackoverflow.com/questions/62289/read-write-to-windows-registry-using-java * * JavaFinder - Windows-specific classes to search for all installed versions of java on this system * Author: petrucio@stackoverflow (828681) *****************************************************************************/ import java.util.*; import java.io.*; /** * Helper class to fetch the stdout and stderr outputs from started Runtime execs * Modified from http://www.javaworld.com/javaworld/jw-12-2000/jw-1229-traps.html?page=4 *****************************************************************************/ class RuntimeStreamer extends Thread { InputStream is; String lines; RuntimeStreamer(InputStream is) { this.is = is; this.lines = ""; } public String contents() { return this.lines; } public void run() { try { InputStreamReader isr = new InputStreamReader(is); BufferedReader br = new BufferedReader(isr); String line = null; while ( (line = br.readLine()) != null) { this.lines += line + "\n"; } } catch (IOException ioe) { ioe.printStackTrace(); } } /** * Execute a command and wait for it to finish * @return The resulting stdout and stderr outputs concatenated ****************************************************************************/ public static String execute(String[] cmdArray) { try { Runtime runtime = Runtime.getRuntime(); Process proc = runtime.exec(cmdArray); RuntimeStreamer outputStreamer = new RuntimeStreamer(proc.getInputStream()); RuntimeStreamer errorStreamer = new RuntimeStreamer(proc.getErrorStream()); outputStreamer.start(); errorStreamer.start(); proc.waitFor(); return outputStreamer.contents() + errorStreamer.contents(); } catch (Throwable t) { t.printStackTrace(); } return null; } public static String execute(String cmd) { String[] cmdArray = { cmd }; return RuntimeStreamer.execute(cmdArray); } } /** * Helper struct to hold information about one installed java version ****************************************************************************/ class JavaInfo { public String path; //! Full path to java.exe executable file public String version; //! Version string. "Unkown" if the java process returned non-standard version string public boolean is64bits; //! true for 64-bit javas, false for 32 /** * Calls 'javaPath -version' and parses the results * @param javaPath: path to a java.exe executable ****************************************************************************/ public JavaInfo(String javaPath) { String versionInfo = RuntimeStreamer.execute( new String[] { javaPath, "-version" } ); String[] tokens = versionInfo.split("\""); if (tokens.length < 2) this.version = "Unkown"; else this.version = tokens[1]; this.is64bits = versionInfo.toUpperCase().contains("64-BIT"); this.path = javaPath; } /** * @return Human-readable contents of this JavaInfo instance ****************************************************************************/ public String toString() { return this.path + ":\n Version: " + this.version + "\n Bitness: " + (this.is64bits ? "64-bits" : "32-bits"); } } /** * Windows-specific java versions finder *****************************************************************************/ public class JavaFinder { /** * @return: A list of javaExec paths found under this registry key (rooted at HKEY_LOCAL_MACHINE) * @param wow64 0 for standard registry access (32-bits for 32-bit app, 64-bits for 64-bits app) * or WinRegistry.KEY_WOW64_32KEY to force access to 32-bit registry view, * or WinRegistry.KEY_WOW64_64KEY to force access to 64-bit registry view * @param previous: Insert all entries from this list at the beggining of the results *************************************************************************/ private static List<String> searchRegistry(String key, int wow64, List<String> previous) { List<String> result = previous; try { List<String> entries = WinRegistry.readStringSubKeys(WinRegistry.HKEY_LOCAL_MACHINE, key, wow64); for (int i = 0; entries != null && i < entries.size(); i++) { String val = WinRegistry.readString(WinRegistry.HKEY_LOCAL_MACHINE, key + "\\" + entries.get(i), "JavaHome", wow64); if (!result.contains(val + "\\bin\\java.exe")) { result.add(val + "\\bin\\java.exe"); } } } catch (Throwable t) { t.printStackTrace(); } return result; } /** * @return: A list of JavaInfo with informations about all javas installed on this machine * Searches and returns results in this order: * HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment (32-bits view) * HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment (64-bits view) * HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Development Kit (32-bits view) * HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Development Kit (64-bits view) * WINDIR\system32 * WINDIR\SysWOW64 ****************************************************************************/ public static List<JavaInfo> findJavas() { List<String> javaExecs = new ArrayList<String>(); javaExecs = JavaFinder.searchRegistry("SOFTWARE\\JavaSoft\\Java Runtime Environment", WinRegistry.KEY_WOW64_32KEY, javaExecs); javaExecs = JavaFinder.searchRegistry("SOFTWARE\\JavaSoft\\Java Runtime Environment", WinRegistry.KEY_WOW64_64KEY, javaExecs); javaExecs = JavaFinder.searchRegistry("SOFTWARE\\JavaSoft\\Java Development Kit", WinRegistry.KEY_WOW64_32KEY, javaExecs); javaExecs = JavaFinder.searchRegistry("SOFTWARE\\JavaSoft\\Java Development Kit", WinRegistry.KEY_WOW64_64KEY, javaExecs); javaExecs.add(System.getenv("WINDIR") + "\\system32\\java.exe"); javaExecs.add(System.getenv("WINDIR") + "\\SysWOW64\\java.exe"); List<JavaInfo> result = new ArrayList<JavaInfo>(); for (String javaPath: javaExecs) { if (!(new File(javaPath).exists())) continue; result.add(new JavaInfo(javaPath)); } return result; } /** * @return: The path to a java.exe that has the same bitness as the OS * (or null if no matching java is found) ****************************************************************************/ public static String getOSBitnessJava() { String arch = System.getenv("PROCESSOR_ARCHITECTURE"); String wow64Arch = System.getenv("PROCESSOR_ARCHITEW6432"); boolean isOS64 = arch.endsWith("64") || (wow64Arch != null && wow64Arch.endsWith("64")); List<JavaInfo> javas = JavaFinder.findJavas(); for (int i = 0; i < javas.size(); i++) { if (javas.get(i).is64bits == isOS64) return javas.get(i).path; } return null; } /** * Standalone testing - lists all Javas in the system ****************************************************************************/ public static void main(String [] args) { List<JavaInfo> javas = JavaFinder.findJavas(); for (int i = 0; i < javas.size(); i++) { System.out.println("\n" + javas.get(i)); } } }
You will also need an updated version of WinRegistry.java to read the values from the 32-bit and 64-bit Windows registry keys: https://stackoverflow.com/a/464829/
I'm usually not a Java programmer, so my code probably doesn't match the java conventions. Sue to me.
Here is an example of starting from a 64-bit Win 7 machine:
>java JavaFinder C:\Program Files (x86)\Java\jre6\bin\java.exe: Version: 1.6.0_31 Bitness: 32-bits C:\Program Files\Java\jre6\bin\java.exe: Version: 1.6.0_31 Bitness: 64-bits D:\Dev\Java\jdk1.6.0_31\bin\java.exe: Version: 1.6.0_31 Bitness: 64-bits C:\Windows\system32\java.exe: Version: 1.6.0_31 Bitness: 64-bits C:\Windows\SysWOW64\java.exe: Version: 1.6.0_31 Bitness: 32-bits
Petrucio
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