How to detect whether java runtime is installed or not on a computer using c#

Question

I program windows applications using Java and this builds a ".jar" file not an ".exe" file. When a client computer with no java runtime installed opens the ".jar" file, it runs as an archive with winrar. All I want to know is how to detect whether java runtime is installed or not on a computer using c# code in order to show a MessageBox telling user to install java runtime, or launches the ".jar" file using the java runtime if it's installed.

Thanks very much :)

Answer 1

You could check in the registry. This will tell you if you have a JRE, and which version.

From this document:

HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Runtime Environment\<version number>
HKEY_LOCAL_MACHINE\Software\JavaSoft\Java Development Kit\<version number>

where the includes the major, minor and the patch version numbers; e.g., 1.4.2_06

Answer 2

You can check the registry

RegistryKey rk = Registry.LocalMachine;
RegistryKey subKey = rk.OpenSubKey("SOFTWARE\\JavaSoft\\Java Runtime Environment");

string currentVerion = subKey.GetValue("CurrentVersion").ToString();

Answer 3

A small applet in a html page which cancels a redirect to a "Please install Java" page.

EDIT: This is almost the only really bullet-proof way. Any registry key containing JavaSoft is most likely only for the Sun JVM and not any other (like IBM or BEA).