Determining where jvm.dll is + extensive CPU usage

Question

Hi,
I am trying to create a JNI wrapper for my java application. I have reached the stage where I can launch the program, providing I have the path to jvm.dll in my path variable.
I was wondering if there was any way to determine this path at runtime, seeming as it is highly unlikely anyone using this program would have it pre-set. I was thinking I could use run a command from within the program to set the path variable temporarily, however how would I determine where their javavm was installed?
Is there no way of shipping the dll with the program?
Also when running my java program through the JNI wrapper it uses about 85 - 90% of my CPU whereas when running it w/o the cpu usage is nominal (about 2 - 10%)
Why is this?

Answer 1

Sorry for the lack of response... Been doing other things and forgot about this post...
First you can search for current version but if your Java >app has a mandatory min version
that must be greater than the current version found then >you could search the keys for max version to see if it fits >to use.My program requires j1.6 though could be downgraded to req 1.5 with the removal of 1 class
]On Windows you read the registry database for this >information.
Specifically you read the value of the string >CurrentVersion from the key >HKEY_LOCAL_MACHINE/SOFTWARE/JavaSoft/Java >Runtime Environment.
Then you use that value to read the value of the string >RuntimeLib
from the key >HKEY_LOCAL_MACHINE/SOFTWARE/JavaSoft/Java >Runtime Environment/{CurrentVersion value}.
This value gives you the absolute path of the jvm.dll file.sorry I probably didn't explain how new I am at JNI. All I have is minimal C++ experience (command line hello world apps and the like), and amateur experimentation with java (only 15, not out of secondary education yet.) How does one go about reading the registry using C/C++, (although I'm sure I could find some documentation somewhere on the net.)
Depends on what you want to do with multiple JREs >installed.get the newest one :)
Basic wrapper code I am using at the moment...: (all I want to do is execute my java app from a .exe file rather than an executable jar)
As you can probably see.. is just a bodge of an example from the internet.
Currently my program searches for jvm.dll from the PATH variable.
#include <stdio.h>
#include <jni.h>
void invoke_class(JNIEnv* env) {
     jclass helloWorldClass;
     jmethodID mainMethod;
     jobjectArray applicationArgs;
     jstring applicationArg0;
     helloWorldClass = (*env)->FindClass(env, "be/bavardage/vocab/VocabGUI");
     mainMethod = (*env)->GetStaticMethodID(env, helloWorldClass, "main", "([Ljava/lang/String;)V");
     applicationArgs = (*env)->NewObjectArray(env, 1, (*env)->FindClass(env, "java/lang/String"), NULL);
     applicationArg0 = (*env)->NewStringUTF(env, "From-C-program");
     (*env)->SetObjectArrayElement(env, applicationArgs, 0, applicationArg0);
     (*env)->CallStaticVoidMethod(env, helloWorldClass, mainMethod, applicationArgs);
int main(int argc, char **argv) {
JavaVM* jvm;
     JNIEnv* env;
     JavaVMInitArgs args;
     JavaVMOption options[1];
     /* There is a new JNI_VERSION_1_4, but it doesn't add anything for the purposes of our example. */
     args.version = JNI_VERSION_1_6;
     args.nOptions = 1;
     //options[0].optionString = "-Djava.class.path=c:\\package\\";
     options[0].optionString = "-Djava.class.path=vocab.jar";
     args.options = options;
     args.ignoreUnrecognized = JNI_FALSE;
     JNI_CreateJavaVM(&jvm, (void **)&env, &args);
     env;
     invoke_class( env );
     while (!(*env)->ExceptionCheck( env )) {
      //nothing
    (*env)->ExceptionCheck( env );
    (*env)->ExceptionDescribe( env );
    (*jvm)->DestroyJavaVM( jvm );
}Message was edited by:
bavardage - used tags...Message was edited by:
bavardage