How should I load native libraries for JNI to avoid an UnsatisfiedLinkError?

Question

I want to use JNI on Ubuntu 8.10, using Eclipse and gcc (the standard one with Ubuntu if there are flavours).

I can't seem to load my library despite the make file creating it successfully.

The main Java class is as follows:

class Hello {
    public native void sayHello();

    static {
        System.loadLibrary("hello.so");
    }

    public static void main(String[] args) {
        Hello h = new Hello();
        h.sayHello();
    }
}

My make file is as such;

    all : hello.so

hello.so : Hello.o
    gcc -shared -o hello.so Hello.o

Hello.o : Hello.c Hello.h
    gcc -I/usr/lib/jvm/java-6-sun/include -I/usr/lib/jvm/java-6-sun/include/linux -c Hello.c -o Hello.o

Hello.h : Hello.class
    javah -jni Hello

clean :
    -del Hello.h
    -del Hello.o

The rest of the code (Hello.c) looks like one would think.

The error I'm getting is as follows;

Exception in thread "main" java.lang.UnsatisfiedLinkError: no hello.so in java.library.path

If I use an explicit path:

System.loadLibrary("/home/gavin/Work/workspace/JNI/hello.so");

Then it works, but I'd much rather not use an explicit path if possible.

Answer 1

As per Pax you should set the library path to where ever Java should look for the library. Your library name should be libhello.so. The call to load the library should then be:

System.loadLibrary("hello");

Linux libraries are referenced by the convention libname.so and loaded based on the name. Here is a link about dynamic linking problems in Java from the SWIG documentation, although you are not using SWIG this section is still relevant.