承接上一篇的AFNetworking3.0源碼理解<一 AFURLRequestSerialization>
關(guān)于iOS端的數(shù)據(jù)解析。平時(shí)開發(fā)中用的最頻繁的當(dāng)屬json解析了，對應(yīng)的af里邊的AFJSONResponseSerializer

先看AFURLRequestSerialization（響應(yīng)數(shù)據(jù)解析的基類）

• @protocol

@protocol AFURLResponseSerialization <NSObject, NSSecureCoding, NSCopying>

/**
 The response object decoded from the data associated with a specified response.

 @param response The response to be processed.
 @param data The response data to be decoded.
 @param error The error that occurred while attempting to decode the response data.

 @return The object decoded from the specified response data.
 */
- (nullable id)responseObjectForResponse:(nullable NSURLResponse *)response
                           data:(nullable NSData *)data
                          error:(NSError * _Nullable __autoreleasing *)error NS_SWIFT_NOTHROW;

@end

這里定義了一個(gè)協(xié)議，協(xié)議中定義了一個(gè)數(shù)據(jù)解析的方法。
這個(gè)數(shù)據(jù)解析的基類通過這個(gè)協(xié)議，分別在不同的子類實(shí)現(xiàn)了不同數(shù)據(jù)類型的解析。
平常的網(wǎng)絡(luò)請求的當(dāng)中，由于業(yè)務(wù)不同，返回的數(shù)據(jù)類型也不同，一般都是直接返回?cái)?shù)據(jù)，業(yè)務(wù)人員實(shí)現(xiàn)自己的業(yè)務(wù)，但是當(dāng)業(yè)務(wù)非常復(fù)雜的時(shí)候，會(huì)導(dǎo)致數(shù)據(jù)解析和業(yè)務(wù)混亂在一起。這樣做了之后，數(shù)據(jù)和業(yè)務(wù)可以分開，寫數(shù)據(jù)的寫數(shù)據(jù)，寫業(yè)務(wù)的寫業(yè)務(wù)，當(dāng)出現(xiàn)問題時(shí)也更容易查找。

• validate響應(yīng)驗(yàn)證

- (BOOL)validateResponse:(NSHTTPURLResponse *)response
                    data:(NSData *)data
                   error:(NSError * __autoreleasing *)error
{
    BOOL responseIsValid = YES;
    NSError *validationError = nil;

    if (response && [response isKindOfClass:[NSHTTPURLResponse class]]) {
        if (self.acceptableContentTypes && ![self.acceptableContentTypes containsObject:[response MIMEType]] &&
            !([response MIMEType] == nil && [data length] == 0)) {//確認(rèn)接收類型，接收類型不符時(shí)

            if ([data length] > 0 && [response URL]) {
                NSMutableDictionary *mutableUserInfo = [@{
                                                          NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: unacceptable content-type: %@", @"AFNetworking", nil), [response MIMEType]],
                                                          NSURLErrorFailingURLErrorKey:[response URL],
                                                          AFNetworkingOperationFailingURLResponseErrorKey: response,
                                                        } mutableCopy];
                if (data) {
                    mutableUserInfo[AFNetworkingOperationFailingURLResponseDataErrorKey] = data;
                }

                validationError = AFErrorWithUnderlyingError([NSError errorWithDomain:AFURLResponseSerializationErrorDomain code:NSURLErrorCannotDecodeContentData userInfo:mutableUserInfo], validationError);
            }

            responseIsValid = NO;
        }

        if (self.acceptableStatusCodes && ![self.acceptableStatusCodes containsIndex:(NSUInteger)response.statusCode] && [response URL]) {//確認(rèn)狀態(tài)碼，狀態(tài)碼不對時(shí)
            NSMutableDictionary *mutableUserInfo = [@{
                                               NSLocalizedDescriptionKey: [NSString stringWithFormat:NSLocalizedStringFromTable(@"Request failed: %@ (%ld)", @"AFNetworking", nil), [NSHTTPURLResponse localizedStringForStatusCode:response.statusCode], (long)response.statusCode],
                                               NSURLErrorFailingURLErrorKey:[response URL],
                                               AFNetworkingOperationFailingURLResponseErrorKey: 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;
}

這一段代碼驗(yàn)證了數(shù)據(jù)響應(yīng)的接收類型和接收狀態(tài)碼，并將NSError拼接返回

JSONResponseSerializer

這個(gè)類在父類的基礎(chǔ)上增加了json解析的方法

- (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;
        }
    }

    id responseObject = nil;
    NSError *serializationError = 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
    BOOL isSpace = [data isEqualToData:[NSData dataWithBytes:" " length:1]];
    if (data.length > 0 && !isSpace) {
        responseObject = [NSJSONSerialization JSONObjectWithData:data options:self.readingOptions error:&serializationError];
    } else {
        return nil;
    }

    if (self.removesKeysWithNullValues && responseObject) {
        responseObject = AFJSONObjectByRemovingKeysWithNullValues(responseObject, self.readingOptions);
    }

    if (error) {
        *error = AFErrorWithUnderlyingError(serializationError, *error);
    }

    return responseObject;
}

移除NSNull鍵的方法

static id AFJSONObjectByRemovingKeysWithNullValues(id JSONObject, NSJSONReadingOptions readingOptions) {
    if ([JSONObject isKindOfClass:[NSArray class]]) {
        NSMutableArray *mutableArray = [NSMutableArray arrayWithCapacity:[(NSArray *)JSONObject count]];
        for (id value in (NSArray *)JSONObject) {
            [mutableArray addObject:AFJSONObjectByRemovingKeysWithNullValues(value, readingOptions)];
        }
        
        return (readingOptions & NSJSONReadingMutableContainers) ? mutableArray : [NSArray arrayWithArray:mutableArray];
    } else if ([JSONObject isKindOfClass:[NSDictionary class]]) {
        NSMutableDictionary *mutableDictionary = [NSMutableDictionary dictionaryWithDictionary:JSONObject];
        for (id <NSCopying> key in [(NSDictionary *)JSONObject allKeys]) {
            id value = (NSDictionary *)JSONObject[key];
            if (!value || [value isEqual:[NSNull null]]) {
                [mutableDictionary removeObjectForKey:key];
            } else if ([value isKindOfClass:[NSArray class]] || [value isKindOfClass:[NSDictionary class]]) {
                mutableDictionary[key] = AFJSONObjectByRemovingKeysWithNullValues(value, readingOptions);
            }
        }
        
        return (readingOptions & NSJSONReadingMutableContainers) ? mutableDictionary : [NSDictionary dictionaryWithDictionary:mutableDictionary];
    }
    
    return JSONObject;
}

數(shù)據(jù)響應(yīng)的這個(gè)類因?yàn)槲抑饕戳薺son的所以內(nèi)容不多。