是否可以在“using”语句中为Web请求嵌入“try / catch”？我的代码是否正确？那是我的要求是：
>想要使用“using”语句来确保在任何情况下都为HttpWebResponse释放资源
>但是如果有异常重新获取HttpWebResponse和“response =(HttpWebResponse)request.GetResponse();”仍然想做一些自定义的东西.特别是.
我的源代码：
var result = new HttpHeaderInfo();
HttpWebRequest request = null;
HttpWebResponse response = null;
using (response)
{
try
{
request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "HEAD";
request.KeepAlive = false;
request.Timeout = Properties.Settings.Default.WebTimeoutDefault;
response = (HttpWebResponse)request.GetResponse();
result.LastModified = response.LastModified;
result.ContentType = response.ContentType;
result.StatusCode = response.StatusCode;
result.ContentLength = response.ContentLength;
}
catch (Exception ex)
{
if (ex is InvalidOperationException ||
ex is ProtocolViolationException ||
ex is WebException)
{
result.HttpError = ex;
result.LastModified = System.DateTime.MinValue;
result.ContentType = null;
}
else { throw; }
}
}
谢谢
解决方法
没关系,但有点多余;在一般意义上,您可以轻松地删除using块,在catch之后添加finally块,并在那里显式调用dispose,这将减少代码中的嵌套.
在更具体的意义上,让我感到困惑的是,在进入using块之前,实际上并没有分配响应,并且显式变量声明在此上下文中是不必要的并且令人困惑.我会把它重写为：
HttpHeaderInfo result;
try
{
var request = (HttpWebRequest)WebRequest.Create(uri);
request.Method = "HEAD";
request.KeepAlive = false;
request.Timeout = Properties.Settings.Default.WebTimeoutDefault;
using (HttpWebResponse response = (HttpWebResponse)request.GetResponse())
{
result = new HttpHeaderInfo();
result.LastModified = response.LastModified;
result.ContentType = response.ContentType;
result.StatusCode = response.StatusCode;
result.ContentLength = response.ContentLength;
}
}
catch (WebException ex)
{
// etc.
}
这比原始形式更清晰.另请注意,我正在捕获WebException,而不是通用的System.Exception.您应该捕获特定的异常类型,而不是捕获一般异常,然后检查它们的类型.