c++调用JAVA

/*
开发环境准备，如在VC6.0中
将目录C:\JDK\include和C:\JDK\include\win32加入到开发环境的Include Files目录中，同时将C:\JDK\lib目录添加到开发环境的Library Files目录中。
*/


//Sample.cpp

#include "windows.h" 
#include "jni.h" 
#include <string> 
#include <iostream> 
using namespace std; 

jstring NewJString(JNIEnv *env, LPCTSTR str); 
string  JStringToCString (JNIEnv *env, jstring str); 

int main() 
{ 
//定义一个函数指针，指身JVM中的JNI_CreateJavaVM函数
typedef jint (WINAPI *PFunCreateJavaVM)(JavaVM **, void **, void *); 

int res; 
JavaVMInitArgs vm_args; 
JavaVMOption options[3]; 
JavaVM *jvm; 
JNIEnv *env; 

/*设置初始化参数*/ 
options[0].optionString = "-Djava.compiler=NONE"; 
//设置Jar classpath,包含自己写好的备调用的java class
options[1].optionString = "-Djava.class.path=.;c:\\"; 
//设置显示消息的类型，debug信息
options[2].optionString = "-verbose:NONE"; 

//设置JRE版本号，低于或等于自己安装的JRE版本
vm_args.version = JNI_VERSION_1_4; 
vm_args.nOptions = 3; 
vm_args.options = options; 
/*该参数指定是否忽略非标准的参数，如果填JNI_FALSE，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
HINSTANCE hInstance = ::LoadLibrary("D:\\Java\\jdk1.6.0_06\\jre\\bin\\client\\jvm.dll"); 
if (hInstance == NULL) 
{ 
return false; 
} 
//取得里面的JNI_CreateJavaVM函数指针
PFunCreateJavaVM funCreateJavaVM = (PFunCreateJavaVM)::GetProcAddress(hInstance, "JNI_CreateJavaVM"); 
//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
const char szTest[] = "Jayce"; 
jstring arg = NewJString(env, szTest); 
jstring msg = (jstring) env->CallObjectMethod(obj, mid, arg, 12); 
cout<<JStringToCString(env, msg); 

//销毁虚拟机并释放动态库
jvm->DestroyJavaVM(); 
::FreeLibrary(hInstance); 
return 0; 
} 

string  JStringToCString (JNIEnv *env, jstring str)// (jstring str, LPTSTR desc, int desc_len) 
{ 
if(str==NULL) 
{ 
return ""; 
} 
//VC中wchar_t用来存储宽字节字符(UNICODE)的数据类型
int len = env->GetStringLength(str); 
wchar_t *w_buffer = new wchar_t[len+1]; 
char *c_buffer = new char[2*len+1]; 
ZeroMemory(w_buffer,(len+1)*sizeof(wchar_t)); 
//使用GetStringChars而不是GetStringUTFChars 
const jchar * jcharString = env->GetStringChars(str, 0); 
wcscpy(w_buffer,jcharString);    
env->ReleaseStringChars(str,jcharString); 
ZeroMemory(c_buffer,(2*len+1)*sizeof(char)); 
len = WideCharToMultiByte(CP_ACP,0,w_buffer,len,c_buffer,2*len,NULL,NULL); 
string cstr = c_buffer; 
delete[] w_buffer; 
delete[] c_buffer; 

return cstr; 
} 

jstring NewJString(JNIEnv *env, LPCTSTR str) 
{ 
if(!env || !str) 
{ 
return 0; 
} 
int slen = strlen(str); 
jchar* buffer = new jchar[slen]; 
int len = MultiByteToWideChar(CP_ACP,0,str,strlen(str),buffer,slen); 
if(len>0 && len < slen) 
{ 
buffer[len]=0; 
} 
jstring js = env->NewString(buffer,len); 
delete [] buffer; 
return js; 
}


//java文件，在C盘建目录test,在test下建Demo.java  ，以下是代码,在test下编译生成Demo.class

package test; 

public class Demo  
{ 

public static int COUNT = 8; 

private String msg; 
private int[] counts; 

public Demo()  
{ 
this("qqqqq"); 
} 

public Demo(String msg)  
{ 
this.msg = msg; 
this.counts = null; 
} 
public String getMessage() 
{ 
return msg; 
} 

public static String getHelloWorld() 
{ 
return "Hello world!"; 
} 


public String append(String str, int i) 
{ 
return str + i; 
} 

public int[] getCounts() 
{ 
return counts; 
} 

public void setCounts(int[] counts) 
{ 
this.counts = counts; 
} 

public void throwExcp()throws IllegalAccessException 
{ 
throw new IllegalAccessException("exception occur."); 
} 
}