目标

1、 Java通过JNI调用C++动态链接库Demo实现全过程,Add decoupling,
包括一个DllA dynamic link library calls the contents of another dynamic link library

2、Implement a pass parameter,and get the return valueJNI项目版本

1、创建C++环境 – 目标功能

1.1 选择Dll模板

1.2 创建第一个dll项目

1.3 新建一个头文件 WindowHidUsb.h 和一个WindowHidUsb.cpp

1.4 修改visual studio dll类型

项目-》属性-》配置管理器-》Win32 改为x64

2、创建一个Java环境

2.1 创建类

package com.mtk.ups.agent.api.usb;

/** * Created with IntelliJ IDEA. * 测试JNI * @author 广大菜鸟 * @since 2022/7/13 22:08 * E-mail: [email protected] */
public class MtkUsbJNI {
    

    /** * 使用dll返回设备数量 * @return 设备数量 */

    native int scanDevice();

}

2.2 用JNI将C++The code header files are born inJavaunder the project source folder

javah -jni -encoding utf-8 com.mtk.ups.agent.api.usb.MtkUsbJNI

3、创建c++环境 – bridge function

创建MtkHidUsbBridge项目

3.1 导入JNI生成.h文件

3.2 创建MtkHidUsbBridge.cpp文件

3.3 关联JNIThe directory corresponding to the generated header file and othersJNI头文件目录,添加到jdk下面

右键 ->属性

Useless words above,则配置所有：右键工程 根目录(https://so.csdn.net/so/search?q=根目录&spm=1001.2101.3001.7020)→ 属性 → 最上面修改为“所有配置”、“所有平台”

添加头文件目录：右键工程根目录→ 属性 → C/C++ → 常规 → 附加包含目录,添加include目录.

运行MtkHidUsbBridge.cpp,生成dll.将dll加入idea环境依赖：project structure -> Librarys -> +号

（后面生成dllall in this way）

4、Test the bridge withjava

MtkUsbJNI.java

package com.mtk.ups.agent.api.usb;

/** * Created with IntelliJ IDEA. * 测试JNI * @author 广大菜鸟 * @since 2022/7/13 22:08 * E-mail: [email protected] */
class MtkUsbJNI {
    

    /** * 使用dll返回设备数量 * @return 设备数量 */

    native int scanDevice();

}

构造MtkUsb单例调用MtkUsbJNI的native方法

package com.mtk.ups.agent.api.usb;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/13 23:53 * E-mail: [email protected] */
public class MtkUsb {
    

    private static final MtkUsb mtkUsb = new MtkUsb();

    private static final MtkUsbJNI mtkUsbJni = new MtkUsbJNI();

    private MtkUsb(){
    }

    public static MtkUsb getInstance(){
    
        return mtkUsb;
    }

    public int scanDevice(){
    
        return mtkUsbJni.scanDevice();
    }
}

构造测试类

package com.mtk.ups.agent.api;

import com.mtk.ups.agent.api.usb.MtkUsb;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/13 23:51 * E-mail: [email protected] */
public class MtkHidUsbTest {
    
    public static void main(String[] args) {
    
        System.loadLibrary("MtkHidUsbBridge");
        System.out.println("Device count = "+ MtkUsb.getInstance().scanDevice());
    }
}

5、修改目标dlland bridgedll,实现解耦

5.1 在目标c++项目内

pch.h

// pch.h: 这是预编译标头文件.
// 下方列出的文件仅编译一次,提高了将来生成的生成性能.
// 这还将影响 IntelliSense 性能,包括代码完成和许多代码浏览功能.
// 但是,如果此处列出的文件中的任何一个在生成之间有更新,它们全部都将被重新编译.
// 请勿在此处添加要频繁更新的文件,这将使得性能优势无效.

#ifndef PCH_H
#define PCH_H

// 添加要在此处预编译的标头
#include "framework.h"
#define API_DLL __declspec(dllexport)

#endif //PCH_H

WindowHidUsb.h

#pragma once
#include "pch.h"
API_DLL int scanDevice();

WindowHidUsb.cpp

#include"WindowHidUsb.h"
#include "pch.h"
API_DLL int scanDevice() {
	return 2;
}

重新生成项目,将Release的.dll文件拷贝到java的src目录下

5.2 在Java项目内,增加dll导入语句

package com.mtk.ups.agent.api;

import com.mtk.ups.agent.api.usb.MtkUsb;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/13 23:51 * E-mail: [email protected] */
public class MtkHidUsbTest {
    
    public static void main(String[] args) {
    
        System.loadLibrary("MtkHidUsb");
        System.loadLibrary("MtkHidUsbBridge");
        System.out.println("Device count = "+ MtkUsb.getInstance().scanDevice());
    }
}

5.3 桥梁项目

5.3.1 Copy the target project'sWindowHidUsb.hfile to the bridge project,并修改内容

#pragma once
#include "pch.h"

#if defined(WIN32)
	#if defined(Release)
		#pragma comment(lib, "C:/Users/Lenovo/Desktop/JNIDemo/MtkHidUsb/x64/Release/MtkHidUsb.lib")
		#pragma message("Automatically linking debug with MtkHidUsb.lib")
	#else
		#pragma comment(lib, "C:/Users/Lenovo/Desktop/JNIDemo/MtkHidUsb/x64/Debug/MtkHidUsb.lib")
		#pragma message("Automatically linking debug with MtkHidUsb.lib")
	#endif
#endif

int scanDevice();

5.3.2 修改 WindowHidUsbBridge.cpp

#include "pch.h"
#include "com_mtk_ups_agent_api_usb_MtkUsbJNI.h"
#include "WindowHidUsb.h"

JNIEXPORT jint JNICALL Java_com_mtk_ups_agent_api_usb_MtkUsbJNI_scanDevice
(JNIEnv*, jobject) {
	//Get it from the underlying library
	return scanDevice();
}

5.3.3 生成新的WindowHidUsbBridge.dll文件,拷贝到java环境,加入依赖

6.进阶–传值

6.1 创建java项目

消息结构体

package com.demo.bean;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/14 23:12 * E-mail: [email protected] */
public class ApiResult {
    
    private int result;
    private String description;

    public int getResult() {
    
        return result;
    }

    public void setResult(int result) {
    
        this.result = result;
    }

    public String getDescription() {
    
        return description;
    }

    public void setDescription(String description) {
    
        this.description = description;
    }
}

Native类

package com.demo.api;

import com.demo.bean.ApiResult;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/14 23:14 * E-mail: [email protected] */
public class NativeApiJni {
    

    native ApiResult getApiResult(int index);

}

编写单例模式 NativeApi

package com.demo.api;

import com.demo.bean.ApiResult;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/14 23:17 * E-mail: [email protected] */
public class NativeApi {
    
    private final NativeApiJni jni = new NativeApiJni();

    private static final NativeApi api = new NativeApi();

    private NativeApi(){
    }

    public static NativeApi getInstance(){
    
        return api;
    }

    public ApiResult getApiResult(int index){
    
        return jni.getApiResult(index);
    }
}

编写测试类

Test.java

package com.demo;


import com.demo.api.NativeApi;
import com.demo.bean.ApiResult;

/** * Created with IntelliJ IDEA. * * @author 广大菜鸟 * @since 2022/7/14 23:16 * E-mail: [email protected] */
public class Test {
    
    public static void main(String[] args) {
    
        System.loadLibrary("ApiNativeDll");

        ApiResult result = NativeApi.getInstance().getApiResult(0);
        System.out.println(result);

        result = NativeApi.getInstance().getApiResult(1);
        System.out.println(result);
    }
}

6.2 创建C++dll项目

ApiNativeDll.cpp

#include"pch.h"
#include"com_demo_api_NativeApiJni.h"
#include"ApiNativeDll.h" // 为空

JNIEXPORT jobject JNICALL Java_com_demo_api_NativeApiJni_getApiResult(JNIEnv* env, jobject, jint jIndex) {
	//获取Java实例
	jclass objectC1ass = env->FindClass("com/demo/bean/ApiResult");
	//Get member variable a constructor
	jmethodID objectC1assInitID = env->GetMethodID(objectC1ass, "<init>", "()V");
	//创建Java对象
	jobject objectNewApiResult = env->NewObject(objectC1ass, objectC1assInitID);
	//获取属性
	jfieldID resultField = env->GetFieldID(objectC1ass, "result", "I");
	jfieldID descriptionField = env->GetFieldID(objectC1ass, "description", "Ljava/lang/String;");
		
	env->SetIntField(objectNewApiResult, resultField, jIndex);
	env->SetObjectField(objectNewApiResult, descriptionField, env->NewStringUTF(jIndex > 0 ? "Failure" : "Success"));
	//或者 调用方法： (*env)->CallVoidMethod(env, obj, mid, depth);
	return objectNewApiResult;
}

The rest of the operations are the same as before,结果是

7.参考学习资料

1. 搭建基本jni项目
   https://www.bilibili.com/video/BV1gq4y1x7Ae
2. 传对象
   https://www.bilibili.com/video/BV1444y1G76L
3. java和c++Corresponding type signature
   https://blog.csdn.net/u013718730/article/details/118067145

补充资料：
Javaeach type and method in ,Both correspond to a unique string,This is the signature

对象类型 An example of a signature is as follows