You can refer to JNI tutorial on sun web site.
Fitsr load library.
Then call  the required method.
Take acre the the dll  must be in path OR keep it in Win32 folder of system

public class Test {
    // Load the dll that exports functions callable from java
    static {System.loadLibrary("TestImp");}

 // Imported function declarations
  public native void print(String msg);

public void Test() {
     }
 public static void main (String ar[]){


 Test t = new Test();
 // Printf example
 t.print("->Testing JNI - Hello from java  to  c++\n");

 }
}