jString to char*
JNIEXPORT void JNICALL Java_ClassName_MethodName(JNIEnv *env, jobject obj, jstring javaString)
{
const char *nativeString = env->GetStringUTFChars(javaString, 0);
// use your string
env->ReleaseStringUTFChars(javaString, nativeString);
}
Exuberant Echidna