C++调用java记录

//http://public0821.iteye.com/blog/423941

//http://blog.csdn.net/chinabinlang/article/details/42527337

#include <QCoreApplication>

#include "jni.h"

#include <string>

#include <stdio.h>

#include <iostream>

#include <QLibrary>

#include <QDir>

using namespace std;

char* jstringTostring(JNIEnv* env, jstring jstr);

jstring stoJstring(JNIEnv* env, const char* pat);

//定义一个函数指针，下面用来指向JVM中的JNI_CreateJavaVM函数

typedef jint (*PFunCreateJavaVM)(JavaVM **, void **, void *);

int main(int argc, char *argv[])

{

QCoreApplication a(argc, argv);

int res;

JavaVMInitArgs vm_args;

JavaVMOption options[4];

JavaVM *jvm;

JNIEnv *env;

/*设置初始化参数*/

//disable JIT，这是JNI文档中的解释，具体意义不是很清楚 ，能取哪些值也不清楚。

//从JNI文档里给的示例代码中搬过来的

options[0].optionString = "-Djava.compiler=NONE";           /* disable JIT */

//设置classpath，如果程序用到了第三方的JAR包，也可以在这里面包含进来

options[1].optionString = "-Djava.class.path=.;E:\\";       /* user classes */

//

options[2].optionString = "-Djava.library.path=.;E:\\test\\lib";     /* set native library path */

//设置显示消息的类型，取值有gc、class和jni，如果一次取多个的话值之间用逗号格开，如-verbose:gc,class

//该参数可以用来观察C++调用JAVA的过程，设置该参数后，程序会在标准输出设备上打印调用的相关信息

options[3].optionString = "-verbose:jni";                   /* print JNI-related messages */

//设置版本号，版本号有JNI_VERSION_1_1，JNI_VERSION_1_2和JNI_VERSION_1_4

//选择一个根你安装的JRE版本最近的版本号即可，不过你的JRE版本一定要等于或者高于指定的版本号

vm_args.version = JNI_VERSION_1_8;

vm_args.options = options;

vm_args.nOptions = 4;

//该参数指定是否忽略非标准的参数，如果填JNI_FLASE，当遇到非标准参数时，JNI_CreateJavaVM会返回JNI_ERR

vm_args.ignoreUnrecognized = JNI_TRUE;

//加载JVM.DLL动态库

QLibrary mylib("D:\\Java\\jdk1.8.0_45\\jre\\bin\\client\\jvm");

if (false == mylib.load())

{

cout << "jvm.dll Load Failed!" << endl;

return 0;

}

else

{

cout << "jvm.dll Load OK!" <<endl;

}

//取得里面的JNI_CreateJavaVM函数指针

PFunCreateJavaVM funCreateJavaVM = (PFunCreateJavaVM)mylib.resolve("JNI_CreateJavaVM");

if (!funCreateJavaVM)

{

cout << "Link to Function JNI_CreateJavaVM Failed!" << endl;

}

else

{

cout << "Link to Function JNI_CreateJavaVM OK!" << endl;

}

//调用JNI_CreateJavaVM创建虚拟机

res = (*funCreateJavaVM)(&jvm, (void**)&env, &vm_args);

if (res < 0)

{

return -1;

}

//查找test.Demo类，返回JAVA类的CLASS对象

jclass cls = env->FindClass("test/Demo");

//根据类的CLASS对象获取该类的实例

jobject obj = env->AllocObject(cls);

//获取类中的方法，最后一个参数是方法的签名，通过javap -s -p 文件名可以获得

jmethodID mid = env->GetMethodID(cls, "append","(Ljava/lang/String;I)Ljava/lang/String;");

//构造参数并调用对象的方法

jstring arg = stoJstring(env, "test_lihailong_");

jstring msg = (jstring) env->CallObjectMethod(obj, mid, arg, 12);

char *output = jstringTostring(env, msg);

cout<< output;

//销毁虚拟机并释放动态库

jvm->DestroyJavaVM();

mylib.unload();

free(output);

return a.exec();

}

char* jstringTostring(JNIEnv* env, jstring jstr)

{

char* rtn = NULL;

jclass clsstring = env->FindClass("java/lang/String");

jstring strencode = env->NewStringUTF("utf-8");

jmethodID mid = env->GetMethodID(clsstring, "getBytes", "(Ljava/lang/String;)[B");

jbyteArray barr= (jbyteArray)env->CallObjectMethod(jstr, mid, strencode);

jsize alen = env->GetArrayLength(barr);

jbyte* ba = env->GetByteArrayElements(barr, JNI_FALSE);

if (alen > 0)

{

rtn = (char*)malloc(alen + 1);

memcpy(rtn, ba, alen);

rtn[alen] = 0;

}

env->ReleaseByteArrayElements(barr, ba, 0);

return rtn;

}

jstring stoJstring(JNIEnv* env, const char* pat)

{

jclass strClass = env->FindClass("Ljava/lang/String;");

jmethodID ctorID = env->GetMethodID(strClass, "<init>", "([BLjava/lang/String;)V");

jbyteArray bytes = env->NewByteArray(strlen(pat));

env->SetByteArrayRegion(bytes, 0, strlen(pat), (jbyte*)pat);

jstring encoding = env->NewStringUTF("utf-8");

return (jstring)env->NewObject(strClass, ctorID, bytes, encoding);

}