JNI开发极简教程-白红宇

JNI（Java Native Interface）

Java调用C/C++，C/C++调用Java的一套API

前言:

学习JNI需要C/C++的相关知识,而且需要研究JNI手册.

想学习的同学,请follow我的学习笔记

1:在eclipse中编写native方法

public class Java2cpp {        static {     System.loadLibrary("Project4");    }     public native int DLL_ADD(int a,int b);//加public native int DLL_SUB(int a,int b);//减public native int DLL_MUL(int a,int b);//乘public native int DLL_DIV(int a,int b);//除    public static void main(String args[]){            int sum = 0;        Java2cpp test = new Java2cpp();    sum = test.DLL_ADD(2, 4);    System.out.println("Java call cpp dll result:" + sum);      }        }}

2.javah命令，生成.h头文件

第一步：javac Java2cpp.java　　生成java2cpp.class

第二步：javah Java2cpp　　生成Java2cpp.h头文件，内容如下：

cmd操作

//生成的C++头文件Java2cpp.h/* DO NOT EDIT THIS FILE - it is machine generated */#include "jni.h"/* Header for class Java2cpp */#ifndef _Included_Java2cpp#define _Included_Java2cpp#ifdef __cplusplusextern "C" {#endif/* * Class:     Java2cpp * Method:    DLL_ADD * Signature: (II)I */JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1ADD  (JNIEnv *, jobject, jint, jint);/* * Class:     Java2cpp * Method:    DLL_SUB * Signature: (II)I */JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1SUB  (JNIEnv *, jobject, jint, jint);/* * Class:     Java2cpp * Method:    DLL_MUL * Signature: (II)I */JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1MUL  (JNIEnv *, jobject, jint, jint);/* * Class:     Java2cpp * Method:    DLL_DIV * Signature: (II)I */JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1DIV  (JNIEnv *, jobject, jint, jint);#ifdef __cplusplus}#endif#endif

3.复制.h头文件,jni.h和jni_md.h到CPP工程中

用visual studio新建空C++项目,引入头文件Java2cpp.h,这边因为没有jni.h和jni_md.h,我们也要导入(jni.h和jni_md.h在jdk的lib中),

项目结构

4.实现.h头文件中声明的函数

编写头文件Java2cpp.h的实现即testdll.cpp.部分代码如下.

#include "Java2cpp.h"/** Class:     Java2cpp* Method:    DLL_ADD* Signature: (II)I*/JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1ADD(JNIEnv *env, jobject obj, jint a, jint b){    int var = 0;    var = a + b;    return var;}/** Class:     Java2cpp* Method:    DLL_SUB* Signature: (II)I*/JNIEXPORT jint JNICALL Java_Java2cpp_DLL_1SUB(JNIEnv *env, jobject obj, jint a, jint b){    int var = 0;    var = a-b;    return var;}

5.生成dll文件

配置文件,右键上3图项目结构选择属性

这里写图片描述

生成解决方案即可

6.配置dll文件所在目录到环境变量

将dll文件所在目录配置到Path中,例如我把dll放在 D:\DllTools ,

则需要将 D:\DllTools; 添加到path的最前面.

7.重启Eclipse

重启查看结果

public class Java2cpp {        static {     System.loadLibrary("Project4");    }     public native int DLL_ADD(int a,int b);//加public native int DLL_SUB(int a,int b);//减public native int DLL_MUL(int a,int b);//乘public native int DLL_DIV(int a,int b);//除    public static void main(String args[]){            int sum = 0;        Java2cpp test = new Java2cpp();    sum = test.DLL_ADD(2, 4);    System.out.println("Java call cpp dll result:" + sum);      }    }

//console 显示的结果Java call cpp dll result:6