How to determine Windows Java installation location

Question

I'm trying to dynamically run a .jar from a C# assembly (using Process.Start(info)). Now, from a console application I am able to just run:

ProcessStartInfo info = new ProcessStartInfo("java", "-jar somerandom.jar");

In an assembly, however, I keep getting a Win32Exception of "The system cannot find the file specified" and have to change the line to the full path of Java like so:

ProcessStartInfo info = new ProcessStartInfo("C:\\Program Files\\Java\\jre6\\bin\\java.exe", "-jar somerandom.jar");

This obviously won't do. I need a way to dynamically (but declaratively) determine the installed location of Java.

I started thinking of looking to the registry, but when I got there I noticed that there were specific keys for the versions and that they could not even be guaranteed to be numeric (e.g. "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.6" and "HKEY_LOCAL_MACHINE\SOFTWARE\JavaSoft\Java Runtime Environment\1.6.0_20").

What would be the most reliable "long-haul" solution to finding the most up-to-date java.exe path from a C# application?

Thanks much in advance.

- EDIT -

Thanks to a combination of GenericTypeTea's and Stephen Cleary's answers, I have solved the issue with the following:

private String GetJavaInstallationPath()
{
    String javaKey = "SOFTWARE\\JavaSoft\\Java Runtime Environment";
    using (var baseKey = RegistryKey.OpenBaseKey(RegistryHive.LocalMachine, RegistryView.Registry64).OpenSubKey(javaKey))
    {
        String currentVersion = baseKey.GetValue("CurrentVersion").ToString();
        using (var homeKey = baseKey.OpenSubKey(currentVersion))
            return homeKey.GetValue("JavaHome").ToString();
    }
}

Answer 1

As far as I know the idea is that the latest version of Java installed on the system is the first one found in the PATH environment variable, so you shouldn't need to look for any registry keys, just run the thing.

Try:

ProcessStartInfo info = new ProcessStartInfo("java.exe", "-jar somerandom.jar");

If it doesn't work make sure java.exe is in your path and let me know.

Answer 2

You can do it through the registry. You were looking in the wrong place though. I knocked together a quick example for you:

private string GetJavaInstallationPath()
{
    string environmentPath = Environment.GetEnvironmentVariable("JAVA_HOME");
    if (!string.IsNullOrEmpty(environmentPath))
    {
       return environmentPath;
    }

    string javaKey = "SOFTWARE\\JavaSoft\\Java Runtime Environment\\";
    using (Microsoft.Win32.RegistryKey rk = Microsoft.Win32.Registry.LocalMachine.OpenSubKey(javaKey))
    {
        string currentVersion = rk.GetValue("CurrentVersion").ToString();
        using (Microsoft.Win32.RegistryKey key = rk.OpenSubKey(currentVersion))
        {
            return key.GetValue("JavaHome").ToString();
        }
    }
}

Then to use it, just do the following:

string installPath = GetJavaInstallationPath();
string filePath = System.IO.Path.Combine(installPath, "bin\\Java.exe");
if (System.IO.File.Exists(filePath))
{
    // We have a winner
}