How to use JNI

JNI allows us to invoke the functionality of the local library in Java code.

Let's take a look at the JNI simple way to use

1. Creating a Java-side interface

1  Public classJniiterface {2 3     //Import the final generated DLL file4     Static {5System.loadlibrary ("Jnidemo");6     }7 8     //declaring an interface implemented in a DLL file9      Public native intMyMethod ();Ten      One      Public native intAddintXinty); A}

2. Generate the header file for the C corresponding to the interface

The Jniiterface class created above, the path to the Jniiterface. class file: \jnidemo\bin\base\jniiterface. class

Execute command under the Bin directory in the project directory: Javah-classpath. -jni base. Jniiterface

The base_jniiterface.h file is then generated in the \jnidemo\bin\ directory

3. Writing an implementation of an interface using Visual Studio

To create a C project, proceed as follows:

The first step:

　　　　　　

Step Two:

　　　　　　

Part III:

　　　　　　

Import the required header files

The header file generated by the second step above, and the jni.h under the Include directory under the JDK root directory, and

The Jni_md.h file under the Win32 directory of the include is copied to the header file directory under the project directory

Create a feature implementation file

Right-click on the source file in the project directory and tap Add-"class

　　　　　　

and write the following code:

1#include"base_jniiterface.h"2#include"jni.h"3#include <stdio.h>4 5 jniexport jint jnicall java_base_jniiterface_mymethod6(JNIENV *, Jobject) {7printf"successfully implement JNI test demo");8       return 0;9 }Ten  One jniexport jint jnicall java_base_jniiterface_add A(JNIENV *, Jobject, jint A, jint b) { -       returnA +b; -}

4. Generating DLL files

Right-click on the solution in the project catalog, select Properties, and make the project as shown

　　　　　　

After compiling the project, it will become a DLL file under the release directory of the project directory.

　　　　　　

5. Configuring the DLL file to Java engineering

First put the DLL file in the Java Project root directory under the Lib directory

Then follow the steps below to add the DLL file as a native library into the project

　　　　　　　　

Edit the native library location as shown, then select the folder where the native library is located in the popup screen:

　　　　　　　　

6. Write test class to verify if JNI is successfully applied

1  Public classHellojni {2 3      Public Static voidMain (string[] args) {4Jniiterface HW =Newjniiterface ();5         intt = Hw.add (3, 7);6         ints =HW. MyMethod ();7 System.out.println (t);8 System.out.println (s);9     }Ten}

The test results after the run are as follows:

Ten 0 success ?? Jni?? DEMO

The most basic steps for using JNI are documented above.

Further exploration is needed on how to use the functionality of a third-party DLL file that has already been written, such as a system DLL file.

Reference article: http://www.runoob.com/w3cnote/jni-getting-started-tutorials.html

How to use JNI