有关C# httpresponse 404 page not found error 的处理方案

需求分析：本人最近做一个项目，项目中需要从新闻的索引页（就是上面有很多链接的那种网页），获取新闻正文页源码，并将新闻正文页源码保存到本地数据库中。
但是由于网络稳定性的原因，总会出现 404 page not found 类型的error。（但是网页是确确实实存在的）。而且这种错误，往往是在程序运行一段时间后出现的，觉得很不可思议。我在网络上查这种问题的解决方案时，发现没有一种管用的。本人现在已经成功解决该问题，遂将自己的解决方案写下来和大家分享与探讨。
解决方案核心：一旦出现这种错误，程序中就递归调用下载函数本身。代码说明如下：

public static string GetDataFromUrl(string url, int nRetryTimes)
{
if (nRetryTimes == 0)
return string.Empty;

string result = string.Empty;
try
{
result=GetDataFromUrl(url);
}
catch (System.Exception exc)
{
if(exc.Message.IndexOf("404")!=-1)
{
result=GetDataFromUrl(url,nRetryTimes-1);
}
}
return result;
}
其中nRetryTimes 代表出现这种错误后，函数递归调用自己的次数，也可以理解为递归终止的条件。GetDataFromUrl(string url)函数代码如下：

public static string GetDataFromUrl(string url)
{
string str = string.Empty;
HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
//设置http头
request.AllowAutoRedirect = true;
request.AllowWriteStreamBuffering = true;
request.Referer = "";
request.Timeout = 10000000;
request.UserAgent = "";
;
request.KeepAlive = false;//to avoid the error of time out
HttpWebResponse response = null;
response = (HttpWebResponse)request.GetResponse();

//根据http应答的http头来判断编码
string characterSet = response.CharacterSet;
Encoding encode;
if (characterSet != "")
{
if (characterSet == "ISO-8859-1")
{
characterSet = "gb2312";
}
encode = Encoding.GetEncoding(characterSet);
}
else
{
encode = Encoding.Default;
}

//声明一个内存流来保存http应答流
Stream receiveStream = response.GetResponseStream();
MemoryStream mStream = new MemoryStream();

byte[] bf = new byte[255];
int count = receiveStream.Read(bf, 0, 255);
while (count > 0)
{
mStream.Write(bf, 0, count);
count = receiveStream.Read(bf, 0, 255);
}
receiveStream.Close();

mStream.Seek(0, SeekOrigin.Begin);

//从内存流里读取字符串
StreamReader reader = new StreamReader(mStream, encode);
char[] buffer = new char[1024];
count = reader.Read(buffer, 0, 1024);
while (count > 0)
{
str += new String(buffer, 0, count);
count = reader.Read(buffer, 0, 1024);
}

//从解析出的字符串里判断charset，如果和http应答的编码不一直
//那么以页面声明的为准，再次从内存流里重新读取文本
Regex reg =
new Regex(@"<meta[\s\S]+?charset=(.*?)""[\s\S]+?>",
RegexOptions.Multiline | RegexOptions.IgnoreCase);
MatchCollection mc = reg.Matches(str);
if (mc.Count > 0)
{
string tempCharSet = mc[0].Result("$1");
if (string.Compare(tempCharSet, characterSet, true) != 0)
{
encode = Encoding.GetEncoding(tempCharSet);
str = string.Empty;
mStream.Seek(0, SeekOrigin.Begin);
reader = new StreamReader(mStream, encode);
buffer = new char[255];
count = reader.Read(buffer, 0, 255);
while (count > 0)
{
str += new String(buffer, 0, count);
count = reader.Read(buffer, 0, 255);
}
}
}
reader.Close();
mStream.Close();
if (response != null)
response.Close();

return str;

}

值得说明的是：尽管采用了此方法，当你查看数据库的时候，你还是会发现有些正文源码没有下载下来。拿我的数据表单来说：我的数据库表单的各个属性如下 ArticlePageId,--数据表的主键。ArticlePageTitle--新闻标题，ArticlePageUrl,--新闻正文页URL，ArticlePageSource--新闻正文页源码，也就是从ArticlePageUrl下载的源码。如果ArticlePageSource字段为空，则表明，下载失败。于是，我又加了一个打补丁的模块。代码如下：

把补丁的模块代码
public static void PatchingUp(string desTable)
{
string conStr = "server=(local);database=ArticleCollection;uid=sa;pwd=123456";
string des = desTable;
string select = string.Format("SELECT ArticlePageId,ArticlePageSource,ArticlePageUrl from {0}", des);
SqlConnection connection = new SqlConnection(conStr);
SqlDataAdapter adapter = new SqlDataAdapter(select, connection);
SqlCommandBuilder builder = new SqlCommandBuilder(adapter);
DataTable table = new DataTable();
adapter.Fill(table);
bool isModified = false;
for (int i = 0; i < table.Rows.Count; i++)
{
if (table.Rows[i]["ArticlePageSource"].ToString() == null || table.Rows[i]["ArticlePageSource"].ToString() == "")
{
Console.WriteLine("在原数据库第{0}行插入失败", i+1);
string url = table.Rows[i]["ArticlePageUrl"].ToString().Trim();
table.Rows[i]["ArticlePageSource"] = ClawlerAssist.GetDataFromUrl(url, 5);

Console.WriteLine("在原数据库第{0}行更新成功", i+1);
if (!isModified)
{
isModified = true;
}

}
}
if (isModified)
{
adapter.Update(table);
}

}

PS：我是新手，这也是我第一次选择首页发帖和大家分享我的一点收获和见解。如有不对的地方还请各位前辈指证。以免误认子弟。