JNI coding

src:
http://blogforopensource.blogspot.tw/2012/08/jni-sample-java-code.html



notes:
15'5/5 :
- javah is used for JNI header
- pay attention to the c compile. It may need extra compiler like VC++




contents:

AUG

22

JNI sample Java Code

Blogging after a long time..


JNI - Java Native Interface.


Java interface to non­Java code.
It is Java's link to the "outside world"

•  Native methods are compiled into a dynamic link
  library (.dll, .so, etc.)
•  OS loads and links the library into the process
  that is running the Java Virtual Machine
•  Part of the Java Developer Kit(JDK),
  serves as a glue between Java side and
  native side of an application
• Allows Java code that runs inside a Java Virtual
  Machine (JVM) to inter operate with applications and
  libraries written in other programming languages,
  such as C, C++, and assembly

JNI w.r.t Operating System :

JNI Sequence:

If you are really interested in JNI,

You can find a Sample Code from here.

http://code.google.com/p/onlineexaminationsysteminjava/downloads/detail?name=samplejnicode.zip&can=2&q=

Reference:

http://patriot.net/~tvalesky/jninative.html

Posted 22nd August 2012 by Srikrishnan's Blog for open source

Labels: JNI sample Java Code

  

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Native Method example using JNI

Trivial JNI example

1. Declare your native methods in an otherwise normal Java class.

   public class nativetest
   {
    public native String sayHello(String s);
    public static void main(String[] argv)
    {
     String retval = null;
     nativetest nt = new nativetest();
     retval = nt.sayHello("Beavis");
     System.out.println("Invocation returned " + retval);
    }
   }
   

2. javac nativetest.java
   Standard Java compile
3. javah -jni nativetest
   Generates .h files. Here is the code.

   /* DO NOT EDIT THIS FILE - it is machine generated */
   #include 
   /* Header for class nativetest */
   
   #ifndef _Included_nativetest
   #define _Included_nativetest
   #ifdef __cplusplus
   extern "C" {
   #endif
   /*
    * Class:     nativetest
    * Method:    sayHello
    * Signature: (Ljava/lang/String;)Ljava/lang/String;
    */
   JNIEXPORT jstring JNICALL Java_nativetest_sayHello
     (JNIEnv *, jobject, jstring);
   
   #ifdef __cplusplus
   }
   #endif
   #endif
   

4. Write your native code, using the .h file generated above Copy the function prototype from the .h file and paste it in.

   #include "nativetest.h" /*double quotes tells it to search current directory*/
   
   JNIEXPORT jstring JNICALL Java_nativetest_sayHello
     (JNIEnv *env, jobject thisobject, jstring js)
   
   {
    return js;
   }
   

5. Compile

   cl -c /Ic:\jdk1.1.6\include /Ic:\jdk1.1.6\include\win32 nativetest.c 
   link /libpath=c:\jdk1.1.6\lib nativetest.obj /dll
   

   The above uses Microsoft Visual C++ command-line tools.
6. Modify your Java class to load the library.

   public class nativetest
   {
    static {
     System.loadLibrary("nativetest");
    }
    public native String sayHello(String s);
    public static void main(String[] argv)
    {
     String retval = null;
     nativetest nt = new nativetest();
     retval = nt.sayHello("Beavis");
     System.out.println("Invocation returned " + retval);
    }
   }
   

7. run the example

   C:\jni\hello>java nativetest
   Invocation returned Beavis
   

8. 
   

notes: