How exactly do I call native static libraries from Java? I'm using Java 8.
It looks to me like I should be able to define a JNI_OnLoad_library in a C++ program with an embedded JVM but my VM keeps dying when I call System.loadLibrary. The following only prints "Hello from main".
main.cpp:
#include <jni.h>
#include <iostream>
extern "C" {
JNIEXPORT jint JNI_OnLoad_hello(JavaVM *vm, void *reserved) {
std::cout << "Hello World" << std::endl;
return JNI_VERSION_1_8;
}
}
int main(int argc, char** argv) {
JavaVM *jvm;
JNIEnv *env;
JavaVMInitArgs vm_args;
jint error;
JavaVMOption* options = new JavaVMOption[argc-1];
for(int i = 0;i < argc-1;i++) {
options[i].optionString = argv[i+1];
}
vm_args.nOptions = argc-1;
vm_args.options = options;
vm_args.version = JNI_VERSION_1_8;
JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
jclass cls = env->FindClass("Main");
jclass stringCls = env->FindClass("java/lang/String");
jmethodID mid = env->GetStaticMethodID(cls, "main", "([Ljava/lang/String;)V");
jobjectArray mainArgs = env->NewObjectArray(0, stringCls, NULL);
env->CallStaticVoidMethod(cls, mid, mainArgs);
jvm->DestroyJavaVM();
}
Main.java:
class Main {
public static void main(String[] args) {
try {
System.out.println("Hello from main");
System.loadLibrary("hello");
System.out.println("Hello after main");
} catch (Exception e) {
e.printStackTrace();
}
}
}
I was finally able to get the JVM to find JNI_OnLoad_hello by passing --export-dynamic to the linker. This allows shared libraries to resolve symbols by looking for them in the executable. Also, System.loadLibrary was throwing UnsatisfiedLikeErrors like I suspected but for some reason I have to handle them in JNI using CheckException and DescribeException.