java 我可以知道调用 JNI C 方法的类的名称吗？
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Can I know the name of the class that calls a JNI C method?
提问by Y.E.P
Is there any way I can know the name of the class that called a method in JNI C code ? I can obtain a reference to the class using the following statement :
有什么办法可以知道在 JNI C 代码中调用方法的类的名称吗？我可以使用以下语句获取对类的引用：
jclass cls = (*env)->GetObjectClass(env,obj);
But is there any way I can know the name of the class ? .
但是有什么办法可以知道班级的名称吗？.
回答by maba
This code will give you the calling class name:
此代码将为您提供调用类名称：
jclass cls = env->GetObjectClass(obj);
// First get the class object
jmethodID mid = env->GetMethodID(cls, "getClass", "()Ljava/lang/Class;");
jobject clsObj = env->CallObjectMethod(obj, mid);
// Now get the class object's class descriptor
cls = env->GetObjectClass(clsObj);
// Find the getName() method on the class object
mid = env->GetMethodID(cls, "getName", "()Ljava/lang/String;");
// Call the getName() to get a jstring object back
jstring strObj = (jstring)env->CallObjectMethod(clsObj, mid);
// Now get the c string from the java jstring object
const char* str = env->GetStringUTFChars(strObj, NULL);
// Print the class name
printf("\nCalling class is: %s\n", str);
// Release the memory pinned char array
env->ReleaseStringUTFChars(strObj, str);
Note that I haven't taken any actions to check for errors. This is just a small code snippet describing how it could be done.
请注意，我没有采取任何措施来检查错误。这只是一个描述如何完成的小代码片段。
Alternatively you could do this instead of using the GetStringUTFChars/ReleaseStringUTFChars:
或者，您可以这样做而不是使用GetStringUTFChars/ReleaseStringUTFChars：
// Make sure that the buffer is large enough
char str[128];
jint strlen = env->GetStringUTFLength(strObj);
env->GetStringUTFRegion(strObj, 0, strlen, str);
printf("\nCalling class is: %s\n", str);
No need to release since the string is copied to local buffer.
由于字符串已复制到本地缓冲区，因此无需释放。
回答by Alexander Haroldo da Rocha
In my case, I haven't had the object to get the class. Instead, I wanted to get the name of a given class, based on its signature.
就我而言，我没有对象来获取课程。相反，我想根据其签名获取给定类的名称。
So, this worked for me. I hope it can help:
所以，这对我有用。我希望它可以帮助：
// Find the class by its JNI signature
jclass cls = env->FindClass(expectedType);
// Get the class object's class descriptor
jclass clsClazz = env->GetObjectClass(cls);
// Find the getSimpleName() method in the class object
jmethodID methodId = env->GetMethodID(clsClazz, "getSimpleName", "()Ljava/lang/String;");
jstring className = (jstring) env->CallObjectMethod(cls, methodId);
// And finally, don't forget to release the JNI objects after usage!!!!
env->DeleteLocalRef(clsClazz);
env->DeleteLocalRef(cls);
回答by user207421
Just invoke getName()on the jclass, also via JNI.
只需调用getName()上jclass，也可以通过JNI。
