How to call getStackTrace method from java native interface (jni)

Question

I am trying to understand the jni with some examples. I am trying to get the java stack trace using jni and so this is what I was doing

HelloJNI.java

package test.com.jni;

public class HelloJNI {
    static {
        System.loadLibrary("hello"); // Load native library at runtime
    }

    private native StackTraceElement[] getStackTraceNative(Throwable throwable);
    private native void printStackTraceNative(Throwable throwable);

    public static void main(String[] args) {
        test();
    }

    public static void test() {
        new HelloJNI().printStackTraceNative(new Throwable()); //Invoke native method
        new HelloJNI().getStackTraceNative(new Throwable());
    }
}

Native code (keeping the error handling out for simplicity)

test_com_jni_HelloJNI.c

JNIEXPORT jobjectArray JNICALL Java_test_com_jni_HelloJNI_getStackTraceNative (JNIEnv * env, jobject object, jthrowable exception) {

    jclass exceptionClazz = (*env)->GetObjectClass(env, exception); 

    jmethodID getStackTraceMethod = (*env)->GetMethodID(env, exceptionClazz, "getStackTrace", "()[Ljava.lang.StackTraceElement");

    jobjectArray stacktraces = (*env)->CallObjectMethod(env, exception, getStackTraceMethod);

    return stacktraces;
}

JNIEXPORT void JNICALL Java_test_com_jni_HelloJNI_printStackTraceNative (JNIEnv * env, jobject object, jthrowable exception) {

    jclass exceptionClazz = (*env)->GetObjectClass(env, exception); // can't fail

    jmethodID printStackTraceMethod = (*env)->GetMethodID(env, exceptionClazz, "printStackTrace", "()V");

    (*env)->CallVoidMethod(env, exception, printStackTraceMethod);
}

Now in this code native printStackTraceNative method works and it prints the stack trace however, getStackTraceNative doesn't. When I check the core dump file it says that java has thrown an exception java/lang/NoSuchMethodError for getStackTrace. I am confused because the parameter I am passing to getStackTraceNative method is of the type throwable and throwable should have the method getStackTrace.

What concept I possibly be missing here, any help on this is appreciated. Thanks

Answer 1

You got the method signature wrong. In method signatures the periods in the qualified class name are replaced by forward slashes. The signature for getStackTrace is therefore ()[Ljava/lang/StackTraceElement; (also note the semicolon)

You can get the method signatures from class files with javap with -s option:

javap -classpath '/path/to/jre/lib/rt.jar' -s java.lang.Throwable