This is an old problem, so I thought I'd write down my current experiences to save others, and myself, pain in future.
You write a native library libFoo.so or foo.dll or libFoo.dylib etc. for Java. And you store it in a convenient location, not a system location, because your software shouldn't meddle with that. To use it you need to call
System.loadLibrary("foo");. This will probably give you: "Exception in thread "main" java.lang.UnsatisfiedLinkError: no foo in java.library.path". Where did I go wrong?
System.loadLibrary looks in the Java library path, "java.library.path". Cool, let's set that in the program, just before we call loadLibrary. We can get some platform-independence by passing in the library path on the commandline:
String old = System.getProperty("java.library.path");
It doesn't find the library because you can't change "java.library.path" after starting the JVM. It just ignores your additional directory.
Everyone says set the environment variable LD_LIBRARY_PATH to (in my case) /usr/local/lib. This doesn't work either. On Linux and OSX at least Java ignores that variable when setting up java.library.path. In any case setting LD_LIBRARY_PATH globally for your application will screw up something else on your system. Not cool.
Third attempt. Set java.library.path on the java commandline:
Now you've changed the JVM so things could go wrong. Instead of having the system default library path where everything is, you've redefined it to a custom location. Unfortunately there's no universal way to ADD /usr/local/lib to java.library.path. So the best you can do is find the java library path on your system (by writing a Java program that outputs
System.getProperty("java.library.path")) and then add /usr/local/lib to that value and finally specify the entire string to java:
This is what I have to do on Mac OSX. Of course it's entirely platform-specific, which is stupid for a programming language that is supposed to be platform-independent. On the other hand this yucky solution is the best one on offer. Since when you've finished developing you'll be running it time and time again on the same platform it probably doesn't matter much.
Alternatively, you could just put your library in the current directory, which will work on Windows (reportedly) and Mac OSX but not Linux.