jstring, char* 变换函数

// jstring To char*
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;
}

// char* To jstring
jstring stringTojstring(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); 
}