Loading Objective-C Libraries From Java

To load Objective-C dynamic libraries into Java applications, use the NSRuntime class. If the libraries are contained within a bundle, using the NSBundle class may be more appropriate.

NSRuntime’s principal method, loadLibrary, takes a String argument identifying the dynamic library to load. The string can be either the absolute path to the library or just the library name. If just the library name is given, either with or without the standard prefix lib or suffix .dylib, NSRuntime searches through a list of directories until it finds the library. For example, to load a library named libMyCode.dylib located at /usr/lib, all of the following works:

NSRuntime.loadLibrary("/usr/lib/libMyCode.dylib");

// Or, if /usr/lib is in the search paths

NSRuntime.loadLibrary("MyCode");

NSRuntime.loadLibrary("libMyCode.dylib");

After loading the library, the library is initialized by calling the function basenameInitialization where basename is the library’s name with the prefix and suffix stripped off. For example, when creating a library named libMyCode.dylib, create a function named MyCodeInitialization to initialize the library when it gets loaded. The function takes no arguments.

If the library is not found or if the library lacks an initialization function, the application exits with an UnsatisfiedLinkError error.

The NSRuntime class manages a list of directories that are searched when you attempt to load a library without providing its absolute path. Initially, the search path includes /usr/lib/java and /usr/local/lib/java. You can add paths to the list by using the method addPathToLibrarySearchPaths. This method takes a single String argument containing the absolute path of the directory to add to the search list. For example, to add /usr/lib to the list, do the following:

NSRuntime.addPathToLibraryPaths("/usr/lib");

To obtain the current list of search paths, invoke librarySearchPaths.