使用JNI进行Java与C/C++语言混合编程

逃离我推掉我的手 2023-06-27 03:47 27阅读 0赞

C++调java

编写Java代码并编译

这段代码非常简单, 有个静态方法和成员方法, 一个public的成员变量

public class Sample2 {
        public String name;
    
        public static String sayHello(String name) {
            return "Hello, " + name + "!";
        }
    
        public String sayHello() {
            return "Hello, " + name + "!";
        }
    }

由于没有定义构造函数, 所以会有一个默认的构造函数.

运行下面的命令编译

javap -s -private Sample2

得到结果：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1bGVpZG5m_size_16_color_FFFFFF_t_70][]

编写C++代码

#include <iostream>
    #include <JavaVM/jni.h>
    #include <string.h>
    #include <stdio.h>
    #include <unistd.h>
    
    
    // 环境变量PATH在windows下和linux下的分割符定义
    #ifdef _WIN32
    #define PATH_SEPARATOR ';'
    #else
    #define PATH_SEPARATOR ':'
    #endif
    using namespace std;
    int main(int argc, const char * argv[]) {
      
        JavaVMOption options[1];
        JNIEnv *env= NULL;
        JavaVM *jvm= NULL;
        JavaVMInitArgs vm_args;
        
        
        jfieldID fid;
        jobject obj;
        
        options[0].optionString = "-Djava.class.path=/Users/yulei/work/C++/C++ Point/c++-java混编";
        memset(&vm_args, 0, sizeof(vm_args));
        vm_args.version = JNI_VERSION_1_4;
        vm_args.nOptions = 1;
        vm_args.options = options;
    
        // 启动虚拟机
        long status = JNI_CreateJavaVM(&jvm, (void**)&env, &vm_args);
        
        if (status != JNI_ERR)
        {
            // 先获得class对象
            jclass cls = env->FindClass("WinFile");
            if ( cls == 0 ) {
                std::cout << "No such class WinFile !" << std::endl;
                jvm->DestroyJavaVM();
                return 1;
            }
            
            if (cls != 0)
            {
                
    //            // 获取方法ID, 通过方法名和签名, 调用静态方法
                jmethodID mid = env->GetStaticMethodID( cls, "sayHello", "(Ljava/lang/String;)Ljava/lang/String;" );
                if ( mid == 0 ) {
                    std::cout << "No such class Method sayHello !" << std::endl;
                    jvm->DestroyJavaVM();
                }
                if (mid != 0)
                {
                    const char* name = "World";
                    jstring arg = (env)->NewStringUTF( name);
                    jstring result = (jstring)(env)->CallStaticObjectMethod( cls, mid, arg);
                    const char* str = (env)->GetStringUTFChars( result, 0);
                    printf("Result of sayHello: %s\n", str);
                    (env)->ReleaseStringUTFChars( result, 0);
                }
    
                /*** 新建一个对象 ***/
                // 调用默认构造函数
                //obj = (*env)->AllocObjdect(env, cls);
    
                // 调用指定的构造函数, 构造函数的名字叫做<init>
                mid = (env)->GetMethodID( cls, "<init>", "()V");
                obj = (env)->NewObject( cls, mid);
                if (obj == 0)
                {
                    printf("Create object failed!\n");
                }
                /*** 新建一个对象 ***/
    
                // 获取属性ID, 通过属性名和签名
                fid = (env)->GetFieldID( cls, "name", "Ljava/lang/String;");
                if (fid != 0)
                {
                    const char* name = "icejoywoo";
                    jstring arg = (env)->NewStringUTF( name);
                    (env)->SetObjectField( obj, fid, arg); // 修改属性
                }
    
                // 调用成员方法
                mid = (env)->GetMethodID( cls, "sayHello", "()Ljava/lang/String;");
                if (mid != 0)
                {
                    jstring result = (jstring)(env)->CallObjectMethod( obj, mid);
                    const char* str = (env)->GetStringUTFChars( result, 0);
                    printf("Result of sayHello: %s\n", str);
                    (env)->ReleaseStringUTFChars( result, 0);
                }
            }
            
            (jvm)->DestroyJavaVM();
            return 0;
        }
        else
        {
            printf("JVM Created failed!\n");
            return -1;
        }
        return 0;
    }

编译运行：

![20200108123010158.png][]

这就是通过JNI实现的C++和java的混编完成了，注意FindClass的java对象路径否则找不到

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1bGVpZG5m_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200102235809622.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3l1bGVpZG5m,size_16,color_FFFFFF,t_70
[20200108123010158.png]: https://img-blog.csdnimg.cn/20200108123010158.png