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JNI socket connection to C++ server

Posted on 2006-11-03
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Last Modified: 2008-01-16
Dear experts,

I need to create a Java program that connect to a server via socket. The server is written in C++, and I have an API.lib and a header file to work with. The API.lib provides me a function void connect () to establish a socket connection. It is easy to build a C++ client using that function.
My question is: Can I create a Java client that connect dicrectly to C++ server using that function? (via JNI)

Does the socket connection is made if I using JNI call the C++ function connect ()? (I will have a JNI style C++ function wrap around that function, off course).


Thanks in advance
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Question by:phongtran72
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Expert Comment

by:jkr
ID: 17871998
>>My question is: Can I create a Java client that connect dicrectly to C++ server using that function? (via
>> JNI)

Once you handed over control to the C/C++ code, you can do anything that is within the capabilities of the language and the supported APIs, so the answer is "yes".

>>Does the socket connection is made if I using JNI call the C++ function connect ()? (I will have a JNI
>>style C++ function wrap around that function, off course).

The idea actually is to create a wrapper, since socket communcations are hardly ever handled within a single function call. You will need to store some data (socket handle etc.) at some place - where will depend on how you design the whole thing.
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Author Comment

by:phongtran72
ID: 17874933

Thanks for your advice. Do you think is it better to write a C++ executable file to handle a socket connection and push data to Java apps using JNI. In this case, JNI functions/methods only handle a data streaming.

Thanks
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Expert Comment

by:jkr
ID: 17882367
That would be an option, too. However, I am not sure whether the IPC overhead will be much different from the one introduced by JNI...
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Author Comment

by:phongtran72
ID: 17891810

What is wrong with my code. I am using VS2005 to build DLL library. (JNI interface)
The error of the code below are: (I'll split 250 points for this question) :)

error C2144: syntax error : 'void' should be preceded by ';'
missing type specifier - int assumed. Note: C++ does not support default-int
syntax error : missing ';' before identifier 'Java_MyInterface_displayConection'
'JNICALL' : illegal use of type 'void'
 error C2065: 'JNIEnv' : undeclared identifier

#include "stdafx.h"
#include <stdlib.h>                        
#include <stdio.h>                        


void getMessage()
{

      fprintf(stderr, "Some message");

}

JNIEXPORT void JNICALL Java_MyInterface_displayConection(JNIEnv *, jobject)
{
      getMessage();      
}
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Author Comment

by:phongtran72
ID: 17891822
There is #include "jni.h" the the code above.
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Author Comment

by:phongtran72
ID: 17892067
Well, this generates error:

#include "jni.h"
#include "stdafx.h"
#include <stdlib.h>                    
#include <stdio.h>      

And this is solution:

#include "stdafx.h"
#include <stdlib.h>                    
#include <stdio.h>
#include "jni.h"

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Accepted Solution

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jkr earned 500 total points
ID: 17892126
Sorry for not being here earlier, "meeting day". Yes, the header files need to be in a certain order sometimes...
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