Java calls the so file generated by C/C ++ in linux

Java calls the so file generated by C/C ++ in linux
1.
CplusUtil. java is a tool class in java web engineering.
The content is as follows:
CplusUtil. java

package cn.undoner.utils;/** * Created by ${undoner<a data-cke-saved-href="mailto:[email protected]" href="mailto:[email protected]"></a>} on 16-2-25. */public class CplusUtil {    public native void sayHello();    static{        System.out.println(System.getProperty("java.library.path"));        System.load("/usr/lib/jvm/java/jre/lib/amd64/server/MyJni.so");    }    public static void main(String[] args){        CplusUtil h = new CplusUtil();        h.sayHello();    }}

2.
You can use the IDE tool (Eclipse, intellij, javac, and so on) to compile the entire project and generate the corresponding class file.
The path of this article is:
/Project name/target/classes/cn/undoner/utils/CplusUtil. class


3. Generate the. h header file for the c function to be called by utils.
Note: When the package name is available, remember to include the package name path when generating the. h header file.
Javah-classpath classes-jni cn. undoner. utils. CplusUtil


File generated: cn_undoner_utils_CplusUtil.h
The content is as follows:

/* DO NOT EDIT THIS FILE - it is machine generated */#include 
 
  /* Header for class cn_undoner_utils_CplusUtil */#ifndef _Included_cn_undoner_utils_CplusUtil#define _Included_cn_undoner_utils_CplusUtil#ifdef __cplusplusextern "C" {#endif/* * Class:     cn_undoner_utils_CplusUtil * Method:    sayHello * Signature: ()V */JNIEXPORT void JNICALL Java_cn_undoner_utils_CplusUtil_sayHello  (JNIEnv *, jobject);#ifdef __cplusplus}#endif#endif
 

4. Compile c Functions
File: MyJni. c
The content is as follows:

#include <jni.h>#include "cn_undoner_utils_CplusUtil.h"#include <stdio.h>JNIEXPORT void JNICALL Java_cn_undoner_utils_CplusUtil_sayHello(JNIEnv *env,jobject obj){    printf("Hello JNI");    return;}</stdio.h></jni.h>

5.
Compile the. c file into. o, and then convert it into a. so or. dll file.
Gcc-fPIC-D_REENTRANT-I/usr/lib/jvm/java/include/linux-c MyJni. c
Generate file: MyJni. o

6.
Compile the. o file into a. so file.
Gcc-shared MyJni. o-o MyJni. so
Generate file: MyJni. so

7.
The path of MyJni. so in this article is:

/Usr/lib/jvm/java/jre/lib/amd64/server/MyJni. so

8.
Execute CplusUtil. class
Run CplusUtil in ide or run the following java command:
Java cn. undoner. utils. CplusUtil

9.
Result:
/Usr/lib/jvm/java/jre/lib/amd64/server:/usr/lib/jvm/java/jre/lib/amd64: /usr/lib/jvm/java/jre /.. /lib/amd64:/home/vobile/java_tool/idea-IU-141.178.9/bin:/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib: /usr/lib
Hello JNI

Note: System. getProperty ("java. library. path") outputs the following information:
/Usr/lib/jvm/java/jre/lib/amd64/server:/usr/lib/jvm/java/jre/lib/amd64: /usr/lib/jvm/java/jre /.. /lib/amd64:/home/vobile/java_tool/idea-IU-141.178.9/bin:/usr/java/packages/lib/amd64:/usr/lib64:/lib64:/lib: /usr/lib