jni.h

[aymane chetibi]

hello all,
I am trying to create a header file from a java program (to integrate a C code with java)

the prblem is that when I compile my c code it does not find <jni.h>

where is this fine supposed to be ?
Is something wrong with the class path?
where can I get this file ?

Thank you

[Jean-Francois Briere]

The jni.h file is under the {JDK_HOME}/include folder. You must specify this folder when compiling your C code.

Example with gcc in command line:
gcc -I $JAVA_HOME/include ...
Example with Ms compiler in command line:
cl.exe /I %JAVA_HOME%\include ...

Regards

[aymane chetibi]

Thank you.
That works.
Now I have another problem.
I created a library but the java code does not know where to find it.
I know I have to make it in some path but I have no idea where I have to put.
pleaaaaaaaaaaaaaaase help.
I am so close to make this work, the last step is to make the path of the library know that run the program.

Here are the error I got when running:

C:\Documents and Settings\Administrator\Desktop\Time>java CPUJavaTest
Exception in thread "main" java.lang.UnsatisfiedLinkError: no libCPUJavaTest in
java.library.path
at java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.lang.Runtime.loadLibrary0(Unknown Source)
at java.lang.System.loadLibrary(Unknown Source)
at CPUJavaTest.<clinit>(CPUJavaTest.java:8)

Thank you.
Regards,

[Paul Clapham]

Where it says "in java.library.path", that means in the directory referred to by that system property. Here's a useful little bit of code:

public class PropertiesTest {
 
  public static void main(String[] args) {
    System.getProperties().list(System.out);
  }
}

Run that. It will list out all your system properties. One of them will be java.library.path, and its value will tell you where to put your compiled library.

[aymane chetibi]

I did.
I got that java.library.path = c:/windows/system32
so I put my complied library there but still same error.
It does not locate the library.
Do I have to restart the system or what ?

Please help.
thanks

[aymane chetibi]

Well I have overcome this problem using System.load() rather than System.loadLibrary().

Now it gives me the following error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: cpuCount
at CPUJavaTest.cpuCount(Native Method)
at CPUJavaTest.main(CPUJavaTest.java:19)

My C code is as follow:

   #include <unistd.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/timeb.h>
#include <time.h>
#include <stdlib.h>
//#include <string>
#include <stdio.h>
#include "CPUJavaTest.h"
 
JNIEXPORT jlong JNICALL Java_CPUJavaTest_cpuCount (JNIEnv *env, jobject obj)
{
clock_t t1;
t1=clock();
return t1;
} 

and my java code is :

   class CPUJavaTest{
 
public static  native long cpuCount(); // here's the definition
static {
System.load("c:\\windows\\system32\\libCPUJavaTest.so");
}
public static void main(String[] args) {
long cputime;
int i,j;
cputime = cpuCount(); // Use the function
for (i=0;i<300000000;i++) j = i*7+5%14;
cputime = cpuCount() - cputime;// and again
System.out.print("CPUTIME:\t" + cputime );
}
 
} 

I have attached evrything you may need to find where this error come from.

PLease help me!!!

Thank you.

[Jean-Francois Briere]

1- Don't name your native library libCPUJavaTest.so. Name it: libCPUJavaTest.dll. This is how the dynamic libraries are named on Windows.

2- Question: Which C compiler do you use?

Regards

[aymane chetibi]

gcc

[aymane chetibi]

even when I named it .dll it doesn't find it.

Thanks alot.

[Henry Wong]

Originally posted by aymane chetibi:
even when I named it .dll it doesn't find it.

Thanks alot.

Try... "CPUJavaTest.dll".

Henry

[aymane chetibi]

It doesn't work either !!!
Here is exactly what I do :

1)) javac CPUJavaTest.java (to compile java code)
2) javah -jni CPUJavaTest (to create header file)
3) gcc -o libCPUJavaTest.dll -O -shared -fPIC CPUJavaTest.c -I C:\j2sdk1.4.2_03\include\win32 -I c:\j2sdk1.4.2_03\include

What are the things (given the code I provided before) that I should change ???

Also I have noticed the following difference:

In this first one, I used : System.loadLibrary("CPUJavaTest.dll"); (with .dll extention)

C:\Documents and Settings\Administrator\Desktop\Time>javac CPUJavaTest.java
C:\Documents and Settings\Administrator\Desktop\Time>javah -jni CPUJavaTest
C:\Documents and Settings\Administrator\Desktop\Time>gcc -o CPUJavaTest.dll -O -
shared -fPIC CPUJavaTest.c -I C:\j2sdk1.4.2_03\include\win32 -I c:\j2sdk1.4.2_03
\include
cc1.exe: warning: -fPIC ignored for target (all code is position independent)

C:\Documents and Settings\Administrator\Desktop\Time>java CPUJavaTest
Exception in thread "main" java.lang.UnsatisfiedLinkError: no CPUJavaTest.dll in
java.library.path
at java.lang.ClassLoader.loadLibrary(Unknown Source)
at java.lang.Runtime.loadLibrary0(Unknown Source)
at java.lang.System.loadLibrary(Unknown Source)
at CPUJavaTest.<clinit>(CPUJavaTest.java:8)

In this second one I used : System.loadLibrary("CPUJavaTest"); (without extention)
and we see that it no more gives the error of not finding the library on the java.library.path but rather the method cpuCount is the problem.

C:\Documents and Settings\Administrator\Desktop\Time>javac CPUJavaTest.java
C:\Documents and Settings\Administrator\Desktop\Time>javah -jni CPUJavaTest
C:\Documents and Settings\Administrator\Desktop\Time>gcc -o CPUJavaTest.dll -O -
shared -fPIC CPUJavaTest.c -I C:\j2sdk1.4.2_03\include\win32 -I c:\j2sdk1.4.2_03
\include
cc1.exe: warning: -fPIC ignored for target (all code is position independent)
C:\Documents and Settings\Administrator\Desktop\Time>java CPUJavaTest
Exception in thread "main" java.lang.UnsatisfiedLinkError: cpuCount
at CPUJavaTest.cpuCount(Native Method)
at CPUJavaTest.main(CPUJavaTest.java:17)

PLeaaaaaaaase help.

Thanks!!!

[Jean-Francois Briere]

Re-write the CPUJavaTest.java file:

class CPUJavaTest {
    public static native long cpuCount();
    static {
        System.loadLibrary("libCPUJavaTest"); // *** important! use loadLibrary() ***
    }
    public static void main(String[] args) {
        long cputime;
        int i, j;
        cputime = cpuCount();
        for (i = 0; i < 300000000; i++)
            j = i * 7 + 5 % 14;
        cputime = cpuCount() - cputime;
        System.out.print("CPUTIME:\t" + cputime );
    }
}

Re-write the CPUJavaTest.c file:

#include <time.h>
#include "CPUJavaTest.h"
 
JNIEXPORT jlong JNICALL Java_CPUJavaTest_cpuCount(JNIEnv * env, jclass cls) /* *** NOT jobject obj if you look at CPUJavaTest.h *** */
{
    clock_t t1;
    
    t1 = clock();
    return t1;
}

Then do the following:

1) javac CPUJavaTest.java
2) javah -jni CPUJavaTest
3) gcc -o libCPUJavaTest.dll -mno-cygwin -shared -Wl,--add-stdcall-alias CPUJavaTest.c -I C:\j2sdk1.4.2_03\include\win32 -I c:\j2sdk1.4.2_03\include

Before executing the Java class be sure that libCPUJavaTest.dll is either in the same folder -or- dll folder specified in the Path -or- dll folder specified in the java.library.path Java property.
You could put the dll on Windows\System32 but ** that is not a good idea **.

So do either:

1) CPUJavaTest.class and libCPUJavaTest.dll are in the same folder abc:
> cd abc
> java CPUJavaTest

2) CPUJavaTest.class is in folder abc and libCPUJavaTest.dll is in folder def:
> set Path=def;%Path%
> cd abc
> java CPUJavaTest

3) CPUJavaTest.class is in folder abc and libCPUJavaTest.dll is in folder def:
> cd abc
> java -Djava.library.path=def CPUJavaTest

Regards

[ May 12, 2006: Message edited by: Jean-Francois Briere ]

[ May 12, 2006: Message edited by: Jean-Francois Briere ]
[ May 12, 2006: Message edited by: Jean-Francois Briere ]

[aymane chetibi]

Thanks a loooooooooooooooooooooooooooooooooooooooooooooooot!
I have no idea what all the options there are for, but it worked.

Do you how to make it work on linux ?