Access java properties from C++/JNI program

Question

Hello all,
Is it possible to access the Java properties of a JNI VM from a C++ program?
If so, could the code or process be explained to me.
I want to be able to identify a specific VM that is retrieved by the JNI_GetCreatedJavaVMs
call. I set a user property when the VM was created, and would like to verify its value
before calling AttachCurrentThread.
Thanks in advance.
Mark

Answer 1

Are you saying that you set a system property (via System.setProperty() or -D)?
If so, just use the JNI invocation API to call System.getProperty().
Without error checking, that looks something like this:bool isMySystem( JNIEnv* env ) {
  const string PropertyName = "IsMySystem";
  jclass systemClass = env->FindClass( "java/lang/System" );
  jmethodID getPropertyMethod = env->GetStaticMethodID( systemClass, "getProperty", "(Ljava/lang/String;)Ljava/lang/String;" );
  jstring propertyNameString = env->NewStringUTF( PropertyName.c_str() );
  jstring propertyString = env->CallStaticObjectMethod( systemClass, getPropertyMethod, propertyNameString );
  if ( propertyString == 0 ) {
    return false;
  const char* property = env->GetStringUTFChars( propertyString, 0 );
  boolean isMine = ! strcmp( property, "Yes" );
  env->ReleaseStringUTFChars( propertyString, property );
  return isMine;
}Using Jace, http://jace.reyelts.com/jace (a free, open-source toolkit), this would look more like:bool isMySystem() {
  String property = System::getProperty( "IsMySystem" );
  return property.isNull() ? false : prop == "Yes";
}In the end, Jace ends up making all of the exact same calls, but you can see how much easier it is to use.
God bless,
-Toby Reyelts