JAVA calls c++ dynamic link library through JNA

JAVA calls c++ dynamic link library through JNA

1. C++ dynamic link library compilation

(1) Operating principle of dynamic link library

(2) Compile command

• gcc -fPIC -i $JAVA_HOME/include -i $JAVA_HOME/include/linux -shared -o lib(name).so (dynamic link library name).c

  	gcc -fPIC -I $JAVA_HOME/include -I $JAVA_HOME/include/linux -shared -o libhello.so hello.c
  

• PIC makes the code segment of the .so file into a real sense of sharing, and it is impossible to build a shared library without the -fPIC option on some architectures.

  
  

2. Java side

(1) Import dependencies

  <dependencies>
        <!-- https://mvnrepository.com/artifact/net.java.dev.jna/jna -->
        <dependency>
            <groupId>net.java.dev.jna</groupId>
            <artifactId>jna</artifactId>
            <version>5.11.0</version>
        </dependency>
    </dependencies>

(2) Code implementation

• Define interface integration Library
• Use Native.load to load the dynamic link library
• Define the functions that need to be used in the interface

package com.ljn.Jna;

import com.sun.jna.Library;
import com.sun.jna.Native;

/**
 * 运行环境是linux,需要打包生成jar文件放到linux环境运行
 */
class HelloJNA {
    
    

    /**
     * 定义一个接口，默认的是继承Library ，如果动态链接库里的函数是以stdcall方式输出的，那么就继承StdCallLibrary
     * 这个接口对应一个动态链接(SO)文件
     */
    public interface LibraryAdd extends Library {
    
    
        // 这里使用绝对路径加载动态链接库
        LibraryAdd LIBRARY_ADD = Native.load("/home/ljn/program/cpp/libhello.so", LibraryAdd.class);

        /**
         * 接口中只需要定义你要用到的函数或者公共变量，不需要的可以不定义
         * 映射libadd.so里面的函数，注意类型要匹配
         */
        int add(int a, int b);
    }

    public static void main(String[] args) {
    
    
        // 调用so映射的接口函数
        int add = LibraryAdd.LIBRARY_ADD.add(10, 15);
        System.out.println("相加结果：" + add);
    }
}

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(3) Packaged as a jar package

3. Integrated operation

• Put the generated dynamic link library in the /home/ljn/program/cpp directory in linux
• Upload the packaged jar package in the /home/ljn/program/cpp directory in linux
  
• Run: java -jar