C++给Java写程序

Posted 2021-12-09 江州益彤

创建一个Java项目，编码选择utf8

编译Java文件生成.h文件


将.h文件拷贝到C++项目中

实现方法

编译生成解决方案，并复制路径E:\\VS2017\\edoyun\\x64\\Release

运行输入结果

进阶：实现手动注册一个实现的方法


完整代码如下：

package eDoYun;

public class NativeClass {
	public native int nativeAdd(int a, int b);

	public native double nativefAdd(double a, double b);

	public static void main(String[] args) {
		System.loadLibrary("edoyun");// 要生成的C++模块

		NativeClass a = new NativeClass();

		a.nativeAdd(10, 20);

		a.nativefAdd(1.234, 2.345);
	}
}

// dllmain.cpp : 定义 DLL 应用程序的入口点。
#include "pch.h"
#include"eDoYun_NativeClass.h"

BOOL APIENTRY DllMain( HMODULE hModule,
                       DWORD  ul_reason_for_call,
                       LPVOID lpReserved
                     )
{
    switch (ul_reason_for_call)
    {
    case DLL_PROCESS_ATTACH:
    case DLL_THREAD_ATTACH:
    case DLL_THREAD_DETACH:
    case DLL_PROCESS_DETACH:
        break;
    }
    return TRUE;
}

//实现方式1：通过命名规则绑定
JNIEXPORT jint JNICALL Java_eDoYun_NativeClass_nativeAdd
(JNIEnv *, jobject, jint a, jint b) {
	//打印日志和a,b的值
	printf("%s(%d):%s a=%d b=%d\\r\\n", __FILE__, __LINE__, __FUNCTION__, a, b);
	return a + b;
}

//实现方式2：手动注册方法绑定
JNIEXPORT jdouble JNICALL nativefAdd
(JNIEnv *, jobject, jdouble a, jdouble b) {
	//打印日志和a,b的值
	printf("%s(%d):%s a=%f b=%f\\r\\n", __FILE__, __LINE__, __FUNCTION__, a, b);
	return a + b;
}


JNIEXPORT jint JNICALL 
JNI_OnLoad(JavaVM* vm, void* reserved) {
	jint result = -1;
	JNIEnv* env = NULL;
	if (vm->GetEnv((void**)&env, JNI_VERSION_1_1) != JNI_OK) {
		printf("%s(%d):%s\\r\\n", __FILE__, __LINE__, __FUNCTION__);
	}
	jclass clz = env->FindClass("eDoYun/NativeClass");
	if (clz == NULL) {
		printf("%s(%d):%s\\r\\n", __FILE__, __LINE__, __FUNCTION__);
		return -1;
	}

	JNINativeMethod methods[] = {
		{(char*)"nativefAdd",(char*)"(DD)D",(void*)&nativefAdd}//"(DD)D"两个参数都是double返回值也是double
	};

	//注册
	result = env->RegisterNatives(clz, methods, sizeof(methods) / sizeof(JNINativeMethod));
	if (result != 0) {
		printf("%s(%d):%s\\r\\n", __FILE__, __LINE__, __FUNCTION__);
		return -1;
	}

	return JNI_VERSION_1_1;
}