How to get the message from a Java exception caught in JNI

Question

I am attempting to catch exceptions being thrown by Java and report the exception message to my own logging framework. However, if I do this, there's an obvious chicken-and-egg problem; I'm trying to get the message using the Java getMessage() call:

jthrowable e = env->ExceptionOccurred();
jclass clazz = env->GetObjectClass(e);
jmethodID getMessage = env->GetMethodID(clazz,
                                        "getMessage",
                                        "()Ljava/lang/String;");

but I can't actually resolve getMessage, because the pending exception causes the JVM to abort when I call GetObjectClass.

Is there a safe way to get the jmethodID for all exceptions up-front? If I Just get the method ID for Throwable.getMessage() at application startup, will that jmethodID be portable to other classes? Or is the appropriate approach to call env->ExceptionClear() and just keep on using the same local jthrowable reference?

Answer 1

The below works; however, I don't know if it's the intended-correct approach:

jthrowable e = env->ExceptionOccurred();
env->ExceptionClear(); // clears the exception; e seems to remain valid

jclass clazz = env->GetObjectClass(e);
jmethodID getMessage = env->GetMethodID(clazz,
                                        "getMessage",
                                        "()Ljava/lang/String;");
jstring message = (jstring)env->CallObjectMethod(e.get(), getMessage);
const char *mstr = env->GetStringUTFChars(message, NULL);
// do whatever with mstr
env->ReleaseStringUTFChars(message, mstr);
env->DeleteLocalRef(message);
env->DeleteLocalRef(clazz);
env->DeleteLocalRef(e);