关于用 AFN请求报错问题

有时候用Java后台接口调试。
使用AFN的时候
直接用 AFHTTPSessionManager 死活请求不进去，请的时候会报 Code=3840 ，请求报出的错误 errorError Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set.
这时候就用
AFHTTPRequestOperationManager *manager = [AFHTTPRequestOperationManager manager]; manager.responseSerializer.acceptableContentTypes = [NSSet setWithObject:@"text/plain"]; //申明返回的结果是json类型 manager.responseSerializer = [AFJSONResponseSerializer serializer]; //申明请求的数据是json类型 manager.requestSerializer=[AFJSONRequestSerializer serializer]; [manager POST:url parameters:params success:^(AFHTTPRequestOperation *operation, id responseObject) { } failure:^(AFHTTPRequestOperation *operation, NSError *error) { }];