Java runtime error with JNI

Question

I am trying to build and run an example jni program. The program is just a sample helloworld program. I did not write it but I assume that it works. I am running this on Linux. There are four files.

HelloNative.c  
HelloNative.h  
HelloNative.java  
HelloNativeTest.java

To build the files, I did

gcc -I/myDir/jdk/include -I/myDir/jdk/include/linux -fPIC -c HelloNative.c  
gcc -shared -o HelloNative.so HelloNative.o  
java *java

Here is the result of the build

HelloNative.c  
HelloNative.h  
     HelloNative.o  
   HelloNativeTest.class  
HelloNative.class  
HelloNative.java  
HelloNative.so  
HelloNativeTest.java

Then I did

setenv LD_LIBRARY_PATH /myDir/myExample:${LD_LIBRARY_PATH}  
java HelloNativeTest

I got the following error

Exception in thread "main" java.lang.UnsatisfiedLinkError: no HelloNative in java.library.path  
        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1734)  
        at java.lang.Runtime.loadLibrary0(Runtime.java:823)  
        at java.lang.System.loadLibrary(System.java:1028)  
        at HelloNative.<clinit>(HelloNative.java:9)  
        at HelloNativeTest.main(HelloNativeTest.java:8)

I checked the LD_LIBRARY_PATH and the HelloClassTest and HelloNative.so, they were all there. I tried to specify the -CLASSPATH also, but that did not seem to matter. Does anyone have any ideas ?

First of all, you shouldn't have the C files have the same name as the Java files. There's — Rafe Kettler
– Rafe Kettler, Commented Oct 7, 2010 at 15:05
The files were from a tutorial package. I did not modify or rename them. I assume they work as is. I could try to modify and rename them. Are you sure that is the problem ? — tadpole
– tadpole, Commented Oct 7, 2010 at 15:13
It might be a good idea to tell people where they can download the sample from so they might try it. Also have you modified anything at all from the sample ? — Romain Hippeau
– Romain Hippeau, Commented Oct 7, 2010 at 21:47

Andy Thomas · Accepted Answer · 2010-10-07 19:07:15Z

1

Do the following, where X="HelloNative".

Give the library a filename following a system-dependent standard. On Linux, name your library libX.so.
Set the java.library.path System property to the directory containing your library.
Call System.loadLibrary("X") where "X" is the cross-platform part of the library name above.

You named your library HelloNative.so; change it to libHelloNative.so.

From http://download.oracle.com/javase/6/docs/technotes/guides/jni/spec/design.html#wp679:

The argument to System.loadLibrary is a library name chosen arbitrarily by the programmer. The system follows a standard, but platform-specific, approach to convert the library name to a native library name. For example, a Solaris system converts the name pkg_Cls to libpkg_Cls.so, while a Win32 system converts the same pkg_Cls name to pkg_Cls.dll.

If you use OSGi in the future, there's an alternative to setting java.library.path.

answered Oct 7, 2010 at 19:07

Andy Thomas

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1 Comment

tadpole Over a year ago

Yes, thank you Andy. Changing the HelloNative.so to libHelloNative.so did the trick.

dogbane · Accepted Answer · 2010-10-07 15:11:11Z

0

You can also try by setting the java.library.path:

java -Djava.library.path=/myDir/myExample HelloNativeTest

answered Oct 7, 2010 at 15:11

dogbane

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1 Comment

tadpole Over a year ago

That option did not make any difference.

Jonathan · Accepted Answer · 2010-10-07 18:47:08Z

0

Did you do a System.loadLibrary() from Java?

answered Oct 7, 2010 at 18:47

Jonathan

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2 Comments

tadpole Over a year ago

Like I said this is straight from Sun Java tutorial package. I assume they know what they are doing. I did check and they did have class HelloNative { public static native void greeting(); static { System.loadLibrary("HelloNative"); } }

Jonathan Over a year ago

Libraries on Linux are expected to begin with "lib". Try renaming to libHelloNative.so?

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