概况：

这部分比较简单，一共有以下几个类：

• AFHTTPResponseSerializer
• AFJSONResponseSerializer : AFHTTPResponseSerializer
• AFXMLParseResponseSerializer : AFHTTPResponseSerializer
• AFXMLDocumentResponseSerializer : AFHTTPResponseSerializer
• AFPropertyListResponseSerializer : AFHTTPResponseSerializer
• AFImageResponseSerializer : AFHTTPResponseSerializer
• AFCompoundResponseSerializer : AFHTTPResponseSerializer

AFHTTPResponseSerializer

这个类主要是验证response合法性，是否是有效的response

validateResponse:data:error:

- (BOOL)validateResponse:(NSHTTPURLResponse *)response
                    data:(NSData *)data
                   error:(NSError * __autoreleasing *)error
 
{
    BOOL responseIsValid = YES;
    NSError *validationError = nil;
    if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {
//acceptableContentTypes里存储了当前serializer支持的content-type，
//可以在不同的子类init方法中指定。有时候，通过charlse去mock请求的response，
//没有通过rewrite功能重写content-type(默认是text/plain)为application/
//json就会被afnetworking显示请求失败，not accept content-type 错误。
        if (self.acceptableContentTypes && ![self.acceptableContentTypes 
            containsObject:[response MIMEType]]) {
 
            if ([data length] > 0 && [response URL]) {
 
                NSMutableDictionary *mutableUserInfo = [@{
 
                                                          NSLocalizedDescriptio
                                                          nKey: [NSString 
                                                          stringWithFormat:NSLo
                                                        calizedStringFromTable(
                                                            @"Request failed:
                                                        unacceptable 
                                                          content-type: %@", @"
                                                          AFNetworking", nil), 
                                                          [response MIMEType]],
 
                                                          NSURLErrorFailingURLE
                                                          rrorKey:[response URL
                                                          ],
 
                                                          AFNetworkingOperation
                                                          FailingURLResponseErr
                                                          orKey: response,
 
                                                        } mutableCopy];
 
                if (data) {
 
                    mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
 
                }
 
                validationError = AFErrorWithUnderlyingError([NSError 
                    errorWithDomain:AFURLResponseSerializationErrorDomain code:
                    NSURLErrorCannotDecodeContentData userInfo:mutableUserInfo]
                    , validationError);
 
            }
 
            responseIsValid = NO;
        }
//acceptableStatusCodes存储了当前serializer支持的返回码，里面的值是在
//AFHTTPResponseSerializer基类
调用init方法中指定的。
        if (self.acceptableStatusCodes && ![self.acceptableStatusCodes 
            containsIndex:(NSUInteger)response.statusCode] && [response URL]) {
 
            NSMutableDictionary *mutableUserInfo = [@{
 
                                               NSLocalizedDescriptionKey: [
                                               NSString stringWithFormat:
                                               NSLocalizedStringFromTable(@"
                                               Request failed: %@ (%ld)", @"
                                               AFNetworking", nil), [
                                               NSHTTPURLResponse 
                                               localizedStringForStatusCode:
                                               response.statusCode], (long)
                                               response.statusCode],
 
                                               NSURLErrorFailingURLErrorKey:[
                                               response URL],
 
                                               AFNetworkingOperationFailingURLR
                                               esponseErrorKey: response,
 
                                       } mutableCopy];
            if (data) {
 
                mutableUserInfo[
                AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
 
            }
 
            validationError = AFErrorWithUnderlyingError([NSError 
                errorWithDomain:AFURLResponseSerializationErrorDomain code:
                NSURLErrorBadServerResponse userInfo:mutableUserInfo], 
                validationError);                
            responseIsValid = NO;
        }
    }
    if (error && !responseIsValid) {
 
        *error = validationError;
 
    }
    return responseIsValid;
}

AFHTTPResponseSerializer

//只做了response的验证逻辑，具体的反序列化在各个子类中实现。
//所有的serializer都要实现这个方法,在网络请求成功返回数据之后，AFNetworking就会调用serializer这个方法来反序列化。
- (id)responseObjectForResponse:(NSURLResponse *)response
                           data:(NSData *)data
                          error:(NSError *__autoreleasing *)error
{
    [self validateResponse:(NSHTTPURLResponse *)response data:data error:error];
    return data;
}

AFJSONResponseSerializer

responseObjectForResponse:data:error

- (id)responseObjectForResponse:(NSURLResponse *)response
                           data:(NSData *)data
                          error:(NSError *__autoreleasing *)error
{
 
    if (![self validateResponse:(NSHTTPURLResponse *)response data:data error:
    error]) {
 
        if (!error || AFErrorOrUnderlyingErrorHasCodeInDomain(*error, 
            NSURLErrorCannotDecodeContentData, 
            AFURLResponseSerializationErrorDomain)) {                
 
            return nil;
 
        }
 
    }
 
    // Workaround for behavior of Rails to return a single space for `head 
    //:ok` (a workaround for a bug in Safari), which is not interpreted as 
    //valid input by NSJSONSerialization.
 
    // See https://github.com/rails/rails/issues/1742
 
    NSStringEncoding stringEncoding = self.stringEncoding;
 
    if (response.textEncodingName) {
 
        CFStringEncoding encoding = CFStringConvertIANACharSetNameToEncoding((
            CFStringRef)response.textEncodingName);
 
        if (encoding != kCFStringEncodingInvalidId) {
            stringEncoding = CFStringConvertEncodingToNSStringEncoding(encoding);
        }
    }
 
    id responseObject = nil;
 
    NSError *serializationError = nil;
 
    @autoreleasepool {
 
        NSString *responseString = [[NSString alloc] initWithData:data encoding
        :stringEncoding];
 
        if (responseString && ![responseString isEqualToString:@" "]) {
 
            // Workaround for a bug in NSJSONSerialization when Unicode 
            //character escape codes are used instead of the actual character
 
            // See http://stackoverflow.com/a/12843465/157142
 
            data = [responseString dataUsingEncoding:NSUTF8StringEncoding];
 
            if (data) {
 
                if ([data length] > 0) {
                    responseObject = [NSJSONSerialization JSONObjectWithData:
                    data options:self.readingOptions error:&serializationError];
                } else {
                    return nil;
                }
 
            } else {
 
                NSDictionary *userInfo = @{
 
                                           NSLocalizedDescriptionKey: 
                                           NSLocalizedStringFromTable(@"Data 
                                           failed decoding as a UTF-8 string", 
                                           @"AFNetworking", nil),
 
                                           NSLocalizedFailureReasonErrorKey: [
                                           NSString stringWithFormat:
                                           NSLocalizedStringFromTable(@"Could 
                                           not decode string: %@", @"
                                           AFNetworking", nil), responseString]
 
                                           };
                serializationError = [NSError errorWithDomain:
                AFURLResponseSerializationErrorDomain code:
                NSURLErrorCannotDecodeContentData userInfo:userInfo];
            }
        }
    }
//1.removesKeysWithNullValues表示当返回的数据dictionary的value为NSNULL的情况的时候，是
//否移除对应键值对。不处理会导致前端crash，如果不设置这个属性，默认是false
//2.self.readingOptions可以根据需求用来设置最后反序列化出字典是否未可变类型(
//NSJSONReadingMutableContainers)，默认是不可变类型
    if (self.removesKeysWithNullValues && responseObject) {
        responseObject = AFJSONObjectByRemovingKeysWithNullValues(
            responseObject, self.readingOptions);
    }
    if (error) {
        *error = AFErrorWithUnderlyingError(serializationError, *error);
    }
    return responseObject;
} 

AFCompoundResponseSerializer

responseObjectForResponse:data:error:

//这个类主要是可以合并多中Serializer的功能，存储在self.responseSerializers集合中。
- (id)responseObjectForResponse:(NSURLResponse *)response
                           data:(NSData *)data
                          error:(NSError *__autoreleasing *)error
 
{
//这里没有调用validateResponse方法，因为这个类处理的不是某一个具体的response类型
    for (id <AFURLResponseSerialization> serializer in self.responseSerializers) {
        if (![serializer isKindOfClass:[AFHTTPResponseSerializer class]]) {
            continue;
        }
 
        NSError *serializerError = nil;
        id responseObject = [serializer responseObjectForResponse:response data:data error:&serializerError];
        if (responseObject) {
            if (error) {
                *error = AFErrorWithUnderlyingError(serializerError, *error);
            }
 
            return responseObject;
        }
 
    }
    return [super responseObjectForResponse:response data:data error:error];
}