How To Call Native (DLL) Code From Java Using JNI (222092)

SUMMARY

• Make sure that you are using a version of Microsoft's SDK for Java that supports JNI. JNI support was added in December of 1998 to SDK version 3.1 and above. For more information, visit the Java lawsuit information center.
• Make sure that the environment variable, CLASSPATH, contains a reference to "[WINDIR]\Java\Classes\Classes.zip" and "C:" (assuming that C: is your development drive).
• Make sure that your "[SDK-Java]\Bin" directory is included in your path (for JavaH, JVC, and JView).
• Make sure that Visual C++ is properly set up for command-line use. See your Visual C++ documentation for details.
• Write your Java code:

  public class TestJNI {
     public native void greetings();
  
     static {
        System.loadLibrary("greet");
     }
  
     public static void main(String args[]) {
        new TestJNI().greetings();
     }
  }
  					

• Compile the Java file:

  jvc TestJNI.java
  					

• Run JavaH on the generated class file:

  javah -jni TestJNI
  					

• Write the C/C++ code based on the generated header file:

  #include "TestJNI.h"
  #include <stdio.h>
  
  JNIEXPORT void JNICALL Java_TestJNI_greetings(JNIEnv *env,jobject jobj) {
     printf("Hello from Visual C++!");
  }
  					

• Compile the C/C++ code:

  cl greet.cpp -Ic:\sdk-java.31\include -Fegreet.dll -MD -LD
  					

• Test the application:

  jview TestJNI