Native DLL functions from Java code

Here is a tiny note on how to invoke native exported DLL functions from Java code in Windows.

According to the Wiki: "Java Native Access (JNA) provides Java programs easy access to native shared libraries without using the Java Native Interface. JNA's design aims to provide native access in a natural way with a minimum of effort. Noboilerplate or generated glue code is required."

I wrote a DLL in FASM to make it more fun.

Lib.asm

1:  format PE GUI 4.0 DLL  
2:  entry DllEntryPoint  
3:    
4:  include 'win32ax.INC'  
5:    
6:  section ".data" data readable writable  
7:  f1_msg db "This is Function 1",0  
8:  f2_msg db "This is Function 2",0  
9:    
10:  section '.text' code readable executable  
11:    
12:  proc DllEntryPoint hinstDLL,fdwReason,lpvReserved  
13:    mov eax,TRUE  
14:    ret  
15:  endp  
16:    
17:  ; VOID Func1  
18:  proc Func1  
19:    invoke MessageBox, 0, addr f1_msg, 0, 0  
20:    ret  
21:  endp  
22:    
23:  ; VOID Func2  
24:  proc Func2  
25:    invoke MessageBox, 0, addr f2_msg, 0, 0  
26:    ret  
27:  endp  
28:    
29:  section '.idata' import data readable writeable  
30:    library user,'USER32.DLL'  
31:    
32:    import user, MessageBox,'MessageBoxA'  
33:    
34:  section '.edata' export data readable  
35:    export 'LIB.DLL', \  
36:      Func1,'Func1', \  
37:      Func2,'Func2'  
38:    
39:  section '.reloc' fixups data readable discardable  
40:    

Load.java

1:  import com.sun.jna.Library;  
2:  import com.sun.jna.Native;  
3:  import com.sun.jna.Platform;  
4:    
5:  public class Load {  
6:    
7:    public interface TestLib extends Library {  
8:      TestLib INSTANCE = (TestLib)  
9:      Native.loadLibrary("Lib",TestLib.class);  
10:    
11:      void Func1();  
12:      void Func2();  
13:    }  
14:    
15:    public static void main(String[] args) {  
16:      System.out.println("Start");  
17:      TestLib.INSTANCE.Func1();  
18:      TestLib.INSTANCE.Func2();  
19:      System.out.println("Done");  
20:    }  
21:  }  

Download JNA and make sure that it is in your CLASSPATH environment variable.
Now, it's time to compile and run.

1:  fasm Lib.asm  
2:  javac Load.java  
3:  jar cvfe Load.jar Load *.class  
4:  java -jar Load.jar  

That's it. Pretty simple.