Provide a method for overriding how a given function is invoked. An instance of this interface may be provided to Native#load(String, Class, java.util.Map) as an entry in the options map with key Library#OPTION_INVOCATION_MAPPER.

This is useful for implementing inlined functions, or functions which are actually C preprocessor macros. Given a native library and JNA interface method, the mapper may provide a handler which implements the desired functionality (which may or may not actually make use of a native method).

For example, the GNU C library remaps the stat function into a call to _xstat with a slight rearrangement of arguments. A mapper for the GNU C library might look like the following:

new InvocationMapper() {
    public InvocationHandler getInvocationHandler(NativeLibrary lib, Method m) {
        if (m.getName().equals("stat")) {
            final Function f = lib.getFunction("_xstat");
            return new InvocationHandler() {
                public Object invoke(Object proxy, Method method, Object[] args) {
                    Object[] newArgs = new Object[args.length+1];
                    System.arraycopy(args, 0, newArgs, 1, args.length);
                    newArgs[0] = Integer.valueOf(3); // _xstat version
                    return f.invoke(newArgs);
                }
            };
        }
        return null;
    }
}

Another situation is where a header provides a function-like macro or inline function definition.

// Original C code (macro and inline variations)
#define allocblock(x) malloc(x * 1024)
static inline void* allocblock(size_t x) { return malloc(x * 1024); }

// Invocation mapping
new InvocationMapper() {
    public InvocationHandler getInvocationHandler(NativeLibrary lib, Method m) {
        if (m.getName().equals("allocblock")) {
            final Function f = lib.getFunction("malloc");
            return new InvocationHandler() {
                public Object invoke(Object proxy, Method method, Object[] args) {
                    args[0] = ((Integer)args[0]).intValue() * 1024;
                    return f.invoke(newArgs);
                }
            };
        }
        return null;
    }
}