How to call a method in DLL in a Java program

Question

I am trying to call a method in a DLL using JNA. So far have loaded the DLL using

Runtime.getRuntime().load("myworkspace/test.dll"); 

This dll contaings a method that I need to access. How can I execute the method present in DLL in my Java file. Do I create an object or something of the DLL and then get the method name after the dot operator.

Answer 1

From the source:

package jnahelloworldtest;  import com.sun.jna.Library; import com.sun.jna.Native; import com.sun.jna.NativeLong; import com.sun.jna.Platform; import com.sun.jna.*;  /** Simple example of native library declaration and usage. */ public class Main {     public interface simpleDLL extends Library {         simpleDLL INSTANCE = (simpleDLL) Native.loadLibrary(             (Platform.isWindows() ? "simpleDLL" : "simpleDLLLinuxPort"), simpleDLL.class);         // it's possible to check the platform on which program runs, for example purposes we assume that there's a linux port of the library (it's not attached to the downloadable project)         byte giveVoidPtrGetChar(Pointer param); // char giveVoidPtrGetChar(void* param);         int giveVoidPtrGetInt(Pointer param);   //int giveVoidPtrGetInt(void* param);         int giveIntGetInt(int a);               // int giveIntGetInt(int a);         void simpleCall();                      // void simpleCall();     }      public static void main(String[] args) {          simpleDLL sdll = simpleDLL.INSTANCE;          sdll.simpleCall();  // call of void function          int a = 3;         int result1 = sdll.giveIntGetInt(a);  // calling function with int parameter&result         System.out.println("giveIntGetInt("+a+"): " + result1);          String testStr = "ToBeOrNotToBe";         Memory mTest = new Memory(testStr.length()+1);  // '+1' remember about extra byte for \0 character!         mTest.setString(0, testStr);         String testReturn = mTest.getString(0); // you can see that String got properly stored in Memory object         System.out.println("String in Memory:"+testReturn);          Memory intMem = new Memory(4);  // allocating space         intMem.setInt(0, 666); // setting allocated memory to an integer         Pointer intPointer = intMem.getPointer(0);          int int1 = sdll.giveVoidPtrGetInt(Pointer.NULL); // passing null, getting default result         System.out.println("giveVoidPtrGetInt(null):" + int1);          int int2 = sdll.giveVoidPtrGetInt(intMem); // passing int stored in Memory object, getting it back        //int int2 = sdll.giveVoidPtrGetInt(intPointer);  causes JVM crash, use memory object directly!         System.out.println("giveVoidPtrGetInt(666):" + int2);          byte char1 = sdll.giveVoidPtrGetChar(Pointer.NULL);  // passing null, getting default result         byte char2 = sdll.giveVoidPtrGetChar(mTest);        // passing string stored in Memory object, getting first letter          System.out.println("giveVoidPtrGetChar(null):" + (char)char1);         System.out.println("giveVoidPtrGetChar('ToBeOrNotToBe'):" + (char)char2);      } }