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C#中HttpWebRequest、WebClient、HttpClient的使用詳解

來(lái)源:本站原創(chuàng)|時(shí)間:2020-01-10|欄目:C#教程|點(diǎn)擊: 次

HttpWebRequest:

命名空間: System.Net,這是.NET創(chuàng)建者最初開(kāi)發(fā)用于使用HTTP請(qǐng)求的標(biāo)準(zhǔn)類。使用HttpWebRequest可以讓開(kāi)發(fā)者控制請(qǐng)求/響應(yīng)流程的各個(gè)方面,如 timeouts, cookies, headers, protocols。另一個(gè)好處是HttpWebRequest類不會(huì)阻塞UI線程。例如,當(dāng)您從響應(yīng)很慢的API服務(wù)器下載大文件時(shí),您的應(yīng)用程序的UI不會(huì)停止響應(yīng)。HttpWebRequest通常和WebResponse一起使用,一個(gè)發(fā)送請(qǐng)求,一個(gè)獲取數(shù)據(jù)。HttpWebRquest更為底層一些,能夠?qū)φ麄€(gè)訪問(wèn)過(guò)程有個(gè)直觀的認(rèn)識(shí),但同時(shí)也更加復(fù)雜一些。

     //POST方法
    public static string HttpPost(string Url, string postDataStr)
    {
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url);
      request.Method = "POST";
      request.ContentType = "application/x-www-form-urlencoded";
      Encoding encoding = Encoding.UTF8;
      byte[] postData = encoding.GetBytes(postDataStr);
      request.ContentLength = postData.Length;
      Stream myRequestStream = request.GetRequestStream();
      myRequestStream.Write(postData, 0, postData.Length);
      myRequestStream.Close();
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      Stream myResponseStream = response.GetResponseStream();
      StreamReader myStreamReader = new StreamReader(myResponseStream, encoding);
      string retString = myStreamReader.ReadToEnd();
      myStreamReader.Close();
      myResponseStream.Close();

      return retString;
    }
    //GET方法
    public static string HttpGet(string Url, string postDataStr)
    {
      HttpWebRequest request = (HttpWebRequest)WebRequest.Create(Url + (postDataStr == "" ? "" : "?") + postDataStr);
      request.Method = "GET";
      request.ContentType = "text/html;charset=UTF-8";
      HttpWebResponse response = (HttpWebResponse)request.GetResponse();
      Stream myResponseStream = response.GetResponseStream();
      StreamReader myStreamReader = new StreamReader(myResponseStream, Encoding.GetEncoding("utf-8"));
      string retString = myStreamReader.ReadToEnd();
      myStreamReader.Close();
      myResponseStream.Close();
      return retString;
    }

WebClient:

命名空間System.Net,WebClient是一種更高級(jí)別的抽象,是HttpWebRequest為了簡(jiǎn)化最常見(jiàn)任務(wù)而創(chuàng)建的,使用過(guò)程中你會(huì)發(fā)現(xiàn)他缺少基本的header,timeoust的設(shè)置,不過(guò)這些可以通過(guò)繼承httpwebrequest來(lái)實(shí)現(xiàn)。相對(duì)來(lái)說(shuō),WebClient比WebRequest更加簡(jiǎn)單,它相當(dāng)于封裝了request和response方法,不過(guò)需要說(shuō)明的是,Webclient和WebRequest繼承的是不同類,兩者在繼承上沒(méi)有任何關(guān)系。使用WebClient可能比HttpWebRequest直接使用更慢(大約幾毫秒),但卻更為簡(jiǎn)單,減少了很多細(xì)節(jié),代碼量也比較少。

public class WebClientHelper
  {
    public static string DownloadString(string url)
    {
      WebClient wc = new WebClient();
      //wc.BaseAddress = url;  //設(shè)置根目錄
      wc.Encoding = Encoding.UTF8;  //設(shè)置按照何種編碼訪問(wèn),如果不加此行,獲取到的字符串中文將是亂碼
      string str = wc.DownloadString(url);
      return str;
    }
    public static string DownloadStreamString(string url)
    {
      WebClient wc = new WebClient();
      wc.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/76.0.3809.132 Safari/537.36");
      Stream objStream = wc.OpenRead(url);
      StreamReader _read = new StreamReader(objStream, Encoding.UTF8);  //新建一個(gè)讀取流,用指定的編碼讀取,此處是utf-8
      string str = _read.ReadToEnd();
      objStream.Close();
      _read.Close();
      return str;
    }

    public static void DownloadFile(string url, string filename)
    {
      WebClient wc = new WebClient();
      wc.DownloadFile(url, filename);   //下載文件
    }

    public static void DownloadData(string url, string filename)
    {
      WebClient wc = new WebClient();
      byte [] bytes = wc.DownloadData(url);  //下載到字節(jié)數(shù)組
      FileStream fs = new FileStream(filename, FileMode.Create);
      fs.Write(bytes, 0, bytes.Length); 
      fs.Flush();
      fs.Close();
    }

    public static void DownloadFileAsync(string url, string filename)
    {
      WebClient wc = new WebClient();
      wc.DownloadFileCompleted += DownCompletedEventHandler;
      wc.DownloadFileAsync(new Uri(url), filename);
      Console.WriteLine("下載中。。。");
    }
    private static void DownCompletedEventHandler(object sender, AsyncCompletedEventArgs e)
    {
      Console.WriteLine(sender.ToString());  //觸發(fā)事件的對(duì)象
      Console.WriteLine(e.UserState);
      Console.WriteLine(e.Cancelled);
      Console.WriteLine("異步下載完成!");
    }

    public static void DownloadFileAsync2(string url, string filename)
    {
      WebClient wc = new WebClient();
      wc.DownloadFileCompleted += (sender, e) =>
      {
        Console.WriteLine("下載完成!");
        Console.WriteLine(sender.ToString());
        Console.WriteLine(e.UserState);
        Console.WriteLine(e.Cancelled);
      };
      wc.DownloadFileAsync(new Uri(url), filename);
      Console.WriteLine("下載中。。。");
    }
  }

HttpClient:

HttpClient是.NET4.5引入的一個(gè)HTTP客戶端庫(kù),其命名空間為 System.Net.Http ,.NET 4.5之前我們可能使用WebClient和HttpWebRequest來(lái)達(dá)到相同目的。HttpClient利用了最新的面向任務(wù)模式,使得處理異步請(qǐng)求非常容易。它適合用于多次請(qǐng)求操作,一般設(shè)置好默認(rèn)頭部后,可以進(jìn)行重復(fù)多次的請(qǐng)求,基本上用一個(gè)實(shí)例可以提交任何的HTTP請(qǐng)求。HttpClient有預(yù)熱機(jī)制,第一次進(jìn)行訪問(wèn)時(shí)比較慢,所以不應(yīng)該用到HttpClient就new一個(gè)出來(lái),應(yīng)該使用單例或其他方式獲取HttpClient的實(shí)例

單例模式:

單例模式(Singleton Pattern)這種類型的設(shè)計(jì)模式屬于創(chuàng)建型模式,它提供了一種創(chuàng)建對(duì)象的最佳方式。

這種模式涉及到一個(gè)單一的類,該類負(fù)責(zé)創(chuàng)建自己的對(duì)象,同時(shí)確保只有單個(gè)對(duì)象被創(chuàng)建。這個(gè)類提供了一種訪問(wèn)其唯一的對(duì)象的方式,可以直接訪問(wèn),不需要實(shí)例化該類的對(duì)象。

單例創(chuàng)建步驟:1、定義靜態(tài)私有對(duì)象;2、定義私有構(gòu)造函數(shù);3、提供公共獲取對(duì)象方法;

單例模式一般分為兩種實(shí)現(xiàn)模式:懶漢模式、餓漢模式(以下為Java代碼實(shí)現(xiàn))

懶漢模式:  默認(rèn)不會(huì)實(shí)例化,什么時(shí)候用什么時(shí)候new

public class Singleton { 
  private static Singleton instance = null; 
  private Singleton (){} 
 
  public static Singleton getInstance() { 
  if (instance == null) { 
    instance = new Singleton(); 
  } 
  return instance; 
  } 
}

這種方式是最基本的實(shí)現(xiàn)方式,這種實(shí)現(xiàn)最大的問(wèn)題就是不支持多線程。因?yàn)闆](méi)有加鎖 synchronized,所以嚴(yán)格意義上它并不算單例模式。
這種方式 lazy loading 很明顯,不要求線程安全,在多線程不能正常工作。

餓漢模式:  類初始化時(shí),會(huì)立即加載該對(duì)象,線程天生安全,調(diào)用效率高

public class Singleton { 
  private static Singleton instance = new Singleton(); 
  private Singleton (){} 
  public static Singleton getInstance() { 
  return instance; 
  } 
}

雙檢鎖/雙重校驗(yàn)鎖(DCL,即 double-checked locking):這種方式采用雙鎖機(jī)制,安全且在多線程情況下能保持高性能

public class Singleton { 
  private volatile static Singleton singleton; 
  private Singleton (){} 
  public static Singleton getSingleton() { 
  if (singleton == null) { 
    synchronized (Singleton.class) { 
    if (singleton == null) { 
      singleton = new Singleton(); 
    } 
    } 
  } 
  return singleton; 
  } 
}

HttpClient:

public class HttpClientHelper
  {
    private static readonly object LockObj = new object();
    private static HttpClient client = null;
    public HttpClientHelper() {
      GetInstance();
    }
    public static HttpClient GetInstance()
    {

      if (client == null)
      {
        lock (LockObj)
        {
          if (client == null)
          {
            client = new HttpClient();
          }
        }
      }
      return client;
    }
    public async Task<string> PostAsync(string url, string strJson)//post異步請(qǐng)求方法
    {
      try
      {
        HttpContent content = new StringContent(strJson);
        content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
        //由HttpClient發(fā)出異步Post請(qǐng)求
        HttpResponseMessage res = await client.PostAsync(url, content);
        if (res.StatusCode == System.Net.HttpStatusCode.OK)
        {
          string str = res.Content.ReadAsStringAsync().Result;
          return str;
        }
        else
          return null;
      }
      catch (Exception ex)
      {
        return null;
      }
    }

    public string Post(string url, string strJson)//post同步請(qǐng)求方法
    {
      try
      {
        HttpContent content = new StringContent(strJson);
        content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue("application/json");
        //client.DefaultRequestHeaders.Connection.Add("keep-alive");
        //由HttpClient發(fā)出Post請(qǐng)求
        Task<HttpResponseMessage> res = client.PostAsync(url, content);
        if (res.Result.StatusCode == System.Net.HttpStatusCode.OK)
        {
          string str = res.Result.Content.ReadAsStringAsync().Result;
          return str;
        }
        else
          return null;
      }
      catch (Exception ex)
      {
        return null;
      }
    }

    public string Get(string url)
    {
      try
      {
        var responseString = client.GetStringAsync(url);
        return responseString.Result;
      }
      catch (Exception ex)
      {
        return null;
      }
    }

  }

HttpClient有預(yù)熱機(jī)制,第一次請(qǐng)求比較慢;可以通過(guò)初始化前發(fā)送一次head請(qǐng)求解決:

_httpClient = new HttpClient() { BaseAddress = new Uri(BASE_ADDRESS) };

    //幫HttpClient熱身
    _httpClient.SendAsync(new HttpRequestMessage {
        Method = new HttpMethod("HEAD"), 
        RequestUri = new Uri(BASE_ADDRESS + "/") })
      .Result.EnsureSuccessStatusCode();

三者區(qū)別列表:

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