Question

I am trying to create a simple example with JNI. I am having trouble compiling the .cpp source file. I will give all the steps that I have done/tried below. I am trying to follow the tutorial found here: http://java.sun.com/docs/books/jni/html/start.html#27008

I have a Java program called HelloJNI.java

public class HelloJNI
{
    private native void print();

    public static void main(String[] args)
    {   
        new HelloJNI().print();
    }

    static
    {
        System.loadLibrary("HelloJNI");
    }
}

From here I compiled the java file and called

javah -jni HelloJNI to generate HelloJNI.h

From here I create the .cpp source file

#include <jni.h>
#include <iostream>
#include "HelloJNI.h"

using namespace std;

JNIEXPORT void JNICALL
Java_HelloJNI_print(JNIEnv *env, jobject obj)
{
  cout << "Hello JNI!" << endl;
  return;
}

Now that I have all of that I try to create the .dll from the source file, I am using this command to run gcc on cygwin (found this command here – http://www.inonit.com/cygwin/jni/helloWorld/c.html):

gcc -mno-cygwin -I$JAVA_HOME/include -I$JAVA_HOME/include/win32 
    -Wl,--add-stdcall-alias -shared -o HelloJNI.dll HelloJNI.c

When I do this I get an error:

HelloJNI.cpp:1:17: fatal error: jni.h: No such file or directory
compilation terminated.

This is where I am stuck, I don’t really know whey the compiler can’t find jni.h it is in the $JAVA_HOME/include directory.

Results from ls $JAVA_HOME/include:

classfile_constants.h  jdwpTransport.h  jvmti.h      win32
jawt.h                 jni.h            jvmticmlr.h

I know it is a lengthy post, but any help would be awesome.

Thanks

Answer 1

I use the following flags to compile:

JDK = "c:/Program Files/Java/jdk1.5.0_22/"
CFLAGS=-Wall -DGCC -DWINDOWS -I$(JDK)/include/win32 -I$(JDK)/include

However, I should mention that I was not able to run my JNI application if the dll was compiled with cygwin gcc. I compiled with the Visual Studio then and it worked.