Invocation API to launch an application

Question

Hi!
Is it really possible to "start " a java VM from an application written in java?
The page: http://java.sun.com/j2se/1.4.2/docs/guide/jni/spec/invocation.html describes some c++ code that shall do the job I guess....?....but I can't say that I understand everything of it....
There isn't a simple step by step tutorial out there which describes how it shall be done?
And what is the "Java application launcher" which the writers of JRE Install Notes 1.4.2 (http://java.sun.com/j2se/1.4.2/jre/install-windows.html) refer to at the bottom of the text?
Final question: which jre shall I download and install - Windows Offline Installation, Multi-language?.....
the tutorial http://java.sun.com/j2se/1.4.2/docs/guide/jni/spec/invocation.html talks about different JVM - jdk 1.1, Netscape ......
Could someone please enlight me in this topic?
Thanks

Answer 1

First of all, I think the "launcher" mentioned in JRE doc is just a terminology and not a concrete entity. I suppose when you change the setting in Netscape or IE so that it can invokes the Java VM automatically each time there's Java code, that's the equivalent of a "launcher". That's why they say if you want to bypass this "launching" mechanism, you can use Invocation API to do it yourself (or invoke it from something other than Netscape or IE, say, your own self-written software).
Normally when you're running a Java program, you're inside a JVM, and there's no need to "start" another VM, right? But, just for discussion purpose, if you really want to start another JVM in another "working" space, then yes, I think you can use the Invocation API to do just that. It's a bit awkward, since you'll have to use JNI to call out from Java to C++, then inside the C++ code, invoke JNI_CreateJavaVM() to create a new JVM and work in there. Then call jvm->DestroyJavaVM when you're done. Note that all JVM run from jvm.dll, so they may decide to recycle the very JVM that you were starting from (thus defeating our purpose). But in my opinion it most likely will not (be recycled) and will be a brandnew JVM.
If you're not sure then try to use the JNI tutorial first. The invocation API is just a part of JNI. Once you're comfortable with calling Java -> C++, then things'll become much clearer.