Package com.sun.jna

Interface InvocationMapper

  • public interface InvocationMapper
    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;
     }
 }
    Author:
    twall

    • Method Detail

      • getInvocationHandler

        InvocationHandler getInvocationHandler​(NativeLibrary lib,
                                       Method m)
        Return an InvocationHandler responsible for handling the invocation of the given method, or null if the default handling should be used. Note that the result of a call to this method with a given library and method may be cached.
        Parameters:
        lib - Target library
        m - Original JNA interface method that was invoked.