JNI date value conversion issue, getting a different long value in C++ - c++

Question

I'm badly stuck in one basic date conversion in jni as the (long) values passed from Java to JNI/C++ are quite different.
My Java date objects are initialized in class as,
Date date1=new Date(1220227200L * 1000);
// If I convert into milliseconds such as
long timeInMillisecond=date1.getTime();
System.out.println (timeInMillisecond )
// it obviously displays 1220227200000
In my native function, i'm retrieving as
jfieldID fid = env->GetFieldID(cls, "date1", "Ljava/util/Date");
// case 1 - value 1
jlong dobject = (jlong) env->GetObjectField(object ,fid);
cout <<dobject; //displays 139757766370904
// case 2 - value 2
long dobject2 = (long) env->GetObjectField(object, fid);
cout <<dobject2; // displays 140031771862616
// case 3 - value 3
long long dobject3 = (long long) env->GetObjectField(object ,fid);
cout <<dobject3; //displays 140456034100824
I wonder what would be the best way to get correct value here from Java in C++. I'm using C++ 11. Some one please help me here.
Update
Sorry guys, i think I misspelled a few variables, so it wasn't dobject2,3 in GetObjectfield (correcting that)and infact rewriting the code here to make it more clear.
//Data.java
class Data {
public long sDate;
public Date schedDate;
....
}
// Test.java
// Native function
public native static void sendEvent(Data EventRec);
Data Rec= new DataRec();
Rec.sDate= 1400754723399L;
Rec.schedDate = new Date(1220227200L * 1000);
sendEvent(Rec);
//C++
JNIEXPORT void JNICALL Java_Test_sendEvent (JNIEnv *env, jclass cls, jobject jobj) {
cls = env->FindClass("Data");
if (cls !=NULL) {
jmethodID ctorID = env->GetMethodID(cls, "<init>","()V");
if (ctorID != NULL) {
jfieldID fidLong = env->GetFieldID(cls, "sDate", "J");
long dObj = (long) env->GetLongField(jobj,fidLong);
cout << "C++ .. Event Date (LONG): " << dObj <<endl; // This is correct
jfieldID fidDate = env->GetFieldID(cls, "schedDate", "Ljava/util/Date");
// Here is the problem area, that I tried to mimic above...
jobject dobject= (env->GetObjectField(jobj,fidDate));
long dobj = env->GetLongField(dobject,fidDate);
// OR
// long dObj2 = (long) env->GetLongField(jobj,fidDate);
// .....
cout << "C++ .. Date (DATE)..." << dobj;
}
}
}

Answer 1

Your JNI code is not accessing the Java objects correctly.
In your Java_Test_sendEvent() implementation, the jclass parameter points to the class type that your public native static void sendEvent(Data EventRec); is declared in (which you did not show), and the jobject parameter points to the Data Rec object that your Java code is passing in to sendEvent().
Also, in your call to env->GetFieldID() for the Date field, you are missing a required semicolon at the end of the type signature string.
Try this instead:
JNIEXPORT void JNICALL Java_Test_sendEvent (JNIEnv *env, jclass cls, jobject EventRec)
{
jclass cls_EventRec = env->GetObjectClass(EventRec);
jfieldID fid_sDate = env->GetFieldID(cls_EventRec, "sDate", "J");
if (!fid_sDate) {
// error handling...
return;
}
jfieldID fid_schedDate = env->GetFieldID(cls_EventRec, "schedDate", "Ljava/util/Date;");
if (!fid_schedDate) {
// error handling...
return;
}
jlong sDate = env->GetLongField(EventRec, fid_sDate);
cout << "C++ .. Event Date (LONG): " << sDate << endl;
jobject schedDate = env->GetObjectField(EventRec, fid_schedDate);
if (schedDate) {
jclass cls_schedDate = env->GetObjectClass(schedDate);
jmethodID mid_getTime = env->GetMethodID(cls_schedDate, "getTime", "()J");
jlong timeInMillisecond = env->CallLongMethod(schedDate, mid_getTime);
cout << "C++ .. Date (DATE)..." << timeInMillisecond << endl;
}
}

Answer 2

You're overlooking something very important:
jfieldID fid = env->GetFieldID(cls, "date1", "Ljava/util/Date;");
jobject dobject = env->GetObjectField(dobject, fid); // Note: "Get Object Field"
This returns a java.util.Date object. You need to call getTime on it as well:
jmethodID mid = env->GetMethodID(cls, "getTime", "()J");
jlong timeInMillisecond = env->CallLongMethod(dobject, mid);