Scala/Java JNA check sharedobject availability

Question

I'm writing a Scala program which uses a C++ shared object, loaded through JNA, to call some custom file reading functions which we have written in C++ and would prefer not to maintain a Java/Scala copy of as well. The program only needs to be Linux compatible.

My question is, what's the appropriate way to check is the shared object is available programatically? If the user has forgotten to add the shared object to their LD_LIBRARY_PATH, the GUI will crash when they try and use some functionality from it. I'd like to do a check at launch time to ensure that the shared object is available - I can attempt to do a read and then catch any errors, but that requires a file to read from and just doesn't feel like the right way to do it.

Any ideas? Many thanks.

Answer 1

If you're loading via JNA, then you can rely on JNA to throw an UnsatisfiedLinkError if it can't find the library or can't load it due to missing dependencies.

System.loadLibrary and System.load depend on java.library.path, which is more or lesss initialized from LD_LIBRARY_PATH and not quite the same thing as JNA's jna.library.path (JNA can be dynamically directed via that variable to search more locations).

Answer 2

If you're relying on people having an external library in their path (instead of using the JNA JAR wrapping features), you can simply check using System.loadLibrary:

~ $ cat x.c
int answer() { return 42; }
~ $ gcc -shared -fPIC -o libx.so x.c
~ $ scala
Welcome to Scala version 2.9.2 (Java HotSpot(TM) 64-Bit Server VM, Java 1.6.0_21).
Type in expressions to have them evaluated.
Type :help for more information.

scala> System.loadLibrary("x")

scala> System.loadLibrary("y")
java.lang.UnsatisfiedLinkError: no y in java.library.path
        at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1734)
        at java.lang.Runtime.loadLibrary0(Runtime.java:823)
[...]