web api返回格式小结：

1.默认是返回xml格式数据，如果需要返回json格式，需要在Global.asax中加入：

GlobalConfiguration.Configuration.Formatters.XmlFormatter.SupportedMediaTypes.Clear();

2.当以string数据类型返回时，默认是加双引号，如果需要将双引号去掉，需要将string类型转换并以HttpResponseMessage类型返回，

string result = "***";

HttpResponseMessage result_return = new HttpResponseMessage();

result_return = new HttpResponseMessage { Content = new StringContent(result, Encoding.GetEncoding("UTF-8"), "text/plain") };

以json格式返回：

Result_return = new HttpResponseMessage { Content = new StringContent(result, Encoding.GetEncoding("UTF-8"), "application/json") };