Question

我需要从URL读取一些数据 - 但是根据字符串（ICAO） - URL有时不存在（它无效）。在这种情况下 - 我应该得到“N / A” - 但这不起作用......只有当所有三个URL都可读时 - 它才有效。

        [Invoke]
    public List<Category> getWeather(string ICAO)
    {
        try
        {
            List<Category> lstcat = new List<Category>();
            Category cat = new Category();
            string fileString;
            bool isexists = FtpDirectoryExists("ftp://tgftp.nws.noaa.gov/data/observations/metar/stations/" + ICAO);
            if (isexists == true)
            {
                WebClient request = new WebClient();
                string url = "http://weather.noaa.gov/pub/data/observations/metar/stations/" + ICAO;
                byte[] newFileData = request.DownloadData(url);
                fileString = System.Text.Encoding.UTF8.GetString(newFileData);
                cat.Cat = "METAR";
                lstcat.Add(cat);
                cat = new Category();
                cat.Cat = fileString;
                lstcat.Add(cat);
                url = "http://weather.noaa.gov/pub/data/forecasts/shorttaf/stations/" + ICAO;
                newFileData = request.DownloadData(url);

                fileString = System.Text.Encoding.UTF8.GetString(newFileData);
                cat = new Category();
                cat.Cat = "Short TAF";
                lstcat.Add(cat);
                cat = new Category();
                cat.Cat = fileString;
                lstcat.Add(cat);

                url = "http://weather.noaa.gov/pub/data/forecasts/taf/stations/" + ICAO;
                newFileData = request.DownloadData(url);

                fileString = System.Text.Encoding.UTF8.GetString(newFileData);
                cat = new Category();
                cat.Cat = "Long TAF";
                lstcat.Add(cat);
                cat = new Category();
                cat.Cat = fileString;
                lstcat.Add(cat);

            }
            else
            {
                fileString = "N/A;N/A";
            }
            return null;
        }
        catch (Exception)
        {

            throw;
        }
    }

Answer 1

创建检查远程文件是否存在的方法。向URl发出Header请求，如果状态代码为200或302，则返回true，否则为false;

HttpWebResponse response = null;
var request = (HttpWebRequest)WebRequest.Create(/* url */);
request.Method = "HEAD";


try
{
    response = (HttpWebResponse)request.GetResponse();
}
catch (WebException ex)
{
    /* A WebException will be thrown if the status of the response is not `200 OK` */
}
finally
{
    // Don't forget to close your response.
    if (response != null)
    {
        response.Close()
    }
}

Answer 2

好的，我想我明白了你想做什么。我重新编写了代码，使其符合实际需要。

现在，Category中的第一个lstcat似乎有第一个网址的描述（例如“METAR”），Category中的第二个lstcat有fileString匹配它，依此类推。这非常模糊和繁琐。相反，要使一个Category对象包含您需要了解的有关URL的所有内容：

public class Category 
{
    public string description;
    public string fileString;
    //Other fields you might use somewhere else...

    public Category(string description, string fileString /*, other fields, if any...*/)
    {
        this.description = description;
        this.fileString = fileString;
        //Initialize others...
    }
}

然后我将所有URL下载代码放入一个单独的函数中，从而消除了原始代码中的所有重复。

[Invoke]
public List<Category> getWeather(string ICAO)
{
    bool isexists = FtpDirectoryExists("ftp://tgftp.nws.noaa.gov/data/observations/metar/stations/" + ICAO);
    if (isexists)
    {
        List<Category> lstcat = new List<Category>();

        addCategoriesToList(
            lstcat,
            "http://weather.noaa.gov/pub/data/observations/metar/stations/" + ICAO,
            "METAR"
        );
        addCategoriesToList(
            lstcat,
            "http://weather.noaa.gov/pub/data/forecasts/shorttaf/stations/" + ICAO,
            "Short TAF"
        );
        addCategoriesToList(
            lstcat,
            "http://weather.noaa.gov/pub/data/forecasts/taf/stations/" + ICAO,
            "Long TAF"
        );

        return lstcat;
    }
    else
    {
        return null;
    }
}

private static void addCategoriesToList(List<Category> lstcat, string url, string description)
{
    string fileString;
    //Use "using" so that `request` always gets cleaned-up:
    using (WebClient request = new WebClient()) 
    {
        try
        {
            byte[] newFileData = request.DownloadData(url);
            fileString = System.Text.Encoding.UTF8.GetString(newFileData);
        }
        catch
        {
            fileString = "N/A";
        }
    }

    lstcat.Add(new Category(description, fileString));
}

我认为这可以更清洁，更直接的方式实现您的目标。如果确实如此，请告诉我！

尝试Catch - URL链接不存在

2 个答案: