Swig: pass byte array in Java to C

I am trying to create Java implementation for passing byte [] to C using Swig.

Swig:

%include "typemaps.i"
%apply(char *STRING, int LENGTH) { (char *buff, int len) }; 
%inline {
   typedef struct {
        char*         buff;        
        int           len;  
  } workit_t;
}

In my generated java class (workit_t.java), the parameter buff is a String, instead of a byte [].

Java:

public void setBuff(String value){
 ... 
}

What am I doing wrong in my swig definition?

When I write a simple swig definition with no struct, I get the desired type of parameter.

Swig:

%include "typemaps.i"
%apply(char *STRING, int LENGTH) { (char *buff1, int *len1) };

Java:

public static void Mathit(byte[] buff1, byte[] buff2) {
...
}