JNI instance 1

1. Write a Java program that contains a native function.

 

package cn.vicky.jni;/** * * @author Vicky.H */public class HelloWorld {    // 1.need a native method    public native void sayHello();    }

2. Compile the Java program.

[Root @ localhost SRC] # tree
.
'-- CN
'-- Vicky
'-- JNI
'-- Helloworld. Java

3 directories, 1 file
[Root @ localhost SRC] # javac cN/Vicky/JNI/helloworld. Java
[Root @ localhost SRC] # tree
.
'-- CN
'-- Vicky
'-- JNI
| -- Helloworld. Class
'-- Helloworld. Java

3 directories, 2 files
[Root @ localhost SRC] # javah CN. Vicky. JNI. helloworld
[Root @ localhost SRC] # tree
.
| -- CN
| '-- Vicky
| '-- JNI
| -- Helloworld. Class
| '-- Helloworld. Java
'-- Cn_vicky_jni_helloworld.h

3 directories, 3 files

If the preceding operations are performed, a corresponding C/C ++ header file is generated.

 

3. Write a C/C ++ dynamic file library.

The dynamic file library in. So format is still written using netbeans + centos. The project directory is as follows:

Cn_vicky_jni_helloworld.h is the header file generated by the javah command. JNI. h and jni_md.h are:

[Root @ localhost SRC] # cd/usr/Java/default/include/
[Root @ localhost include] # tree
.
| -- Classfile_constants.h
| -- Jawt. h
| -- Jdwptransport. h
| -- JNI. h
| -- Jvmti. h
'-- Linux
| -- Jawt_md.h
'-- Jni_md.h

1 directory, 7 files

Copy the corresponding file.

Compile the header file: cn_vicky_jni_helloworld_impl.cpp

#include "cn_vicky_jni_HelloWorld.h"#include <iostream>using namespace std;JNIEXPORT void JNICALL Java_cn_vicky_jni_HelloWorld_sayHello (JNIEnv *env, jobject obj){    cout << "hello world" << endl;}

Is a simple program that outputs "Hello World. Generate a program: Obtain the dynamic link library of libjni_01_cpp.so. To only use this dynamic link library, we need to copy it to the/usr/lib file.

 

4. Java calls libjni_01_cpp.so

Continue to write the helloworld. Java program

package cn.vicky.jni;/** * * @author Vicky.H */public class HelloWorld {    // 1.need a native method    public native void sayHello();        public static void main(String[] args) {        System.loadLibrary("jni_01_cpp");        new HelloWorld().sayHello();    }}

 

[Vicky @ localhost SRC] $ javac cN/Vicky/JNI/helloworld. Java
[Vicky @ localhost SRC] $ tree
.
| -- CN
| '-- Vicky
| '-- JNI
| -- Helloworld. Class
| '-- Helloworld. Java
'-- Cn_vicky_jni_helloworld.h

3 directories, 3 files
[Vicky @ localhost SRC] $ Java CN. Vicky. JNI. helloworld
Hello World

Program Execution, complete. Delete the dynamic link library used for testing:

[Root @ localhost SRC] # rm/usr/lib/libjni_01_cpp.so
RM: Do you want to delete the common file "/usr/lib/libjni_01_cpp.so "? Y

 

Certificate ------------------------------------------------------------------------------------------------------------------------------------------------------------------------

 

The above is used by JNI in Linux. For Windows, it is basically the same. When the jni_01_cpp.dll file is generated, we need to address the directory where jni_01_cpp.dll is located, baby to the path in windows. For example:

Then run the helloworld program.