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 Summary

Modifier and Type	Method and Description
java.lang.reflect.InvocationHandler	getInvocationHandler(NativeLibrary lib, java.lang.reflect.Method m) Return an InvocationHandler responsible for handling the invocation of the given method, or null if the default handling should be used.

Method Detail

getInvocationHandler

java.lang.reflect.InvocationHandler getInvocationHandler(NativeLibrary lib,
                                                         java.lang.reflect.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.