• C#中HttpWebRequest、WebClient、HttpClient的使用详解


    转自:https://spidersharp.com/?p=838

    C#中HttpWebRequest、WebClient、HttpClient的使用详解

    HttpWebRequest:

    命名空间: System.Net,这是.NET创建者最初开发用于使用HTTP请求的标准类。使用HttpWebRequest可以让开发者控制请求/响应流程的各个方面,如 timeouts, cookies, headers, protocols。另一个好处是HttpWebRequest类不会阻塞UI线程。例如,当您从响应很慢的API服务器下载大文件时,您的应用程序的UI不会停止响应。HttpWebRequest通常和WebResponse一起使用,一个发送请求,一个获取数据。HttpWebRquest更为底层一些,能够对整个访问过程有个直观的认识,但同时也更加复杂一些。

    //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:

    命名空间System.Net,WebClient是一种更高级别的抽象,是HttpWebRequest为了简化最常见任务而创建的,使用过程中你会发现他缺少基本的header,timeoust的设置,不过这些可以通过继承httpwebrequest来实现。相对来说,WebClient比WebRequest更加简单,它相当于封装了request和response方法,不过需要说明的是,Webclient和WebRequest继承的是不同类,两者在继承上没有任何关系。使用WebClient可能比HttpWebRequest直接使用更慢(大约几毫秒),但却更为简单,减少了很多细节,代码量也比较少。

    public class WebClientHelper
    {
    public static string DownloadString(string url)
    {
    WebClient wc = new WebClient();
    //wc.BaseAddress = url; //设置根目录
    wc.Encoding = Encoding.UTF8; //设置按照何种编码访问,如果不加此行,获取到的字符串中文将是乱码
    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); //新建一个读取流,用指定的编码读取,此处是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); //下载文件
    }
     
    public static void DownloadData(string url, string filename)
    {
    WebClient wc = new WebClient();
    byte [] bytes = wc.DownloadData(url); //下载到字节数组
    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("下载中。。。");
    }
    private static void DownCompletedEventHandler(object sender, AsyncCompletedEventArgs e)
    {
    Console.WriteLine(sender.ToString()); //触发事件的对象
    Console.WriteLine(e.UserState);
    Console.WriteLine(e.Cancelled);
    Console.WriteLine("异步下载完成!");
    }
     
    public static void DownloadFileAsync2(string url, string filename)
    {
    WebClient wc = new WebClient();
    wc.DownloadFileCompleted += (sender, e) =>
    {
    Console.WriteLine("下载完成!");
    Console.WriteLine(sender.ToString());
    Console.WriteLine(e.UserState);
    Console.WriteLine(e.Cancelled);
    };
    wc.DownloadFileAsync(new Uri(url), filename);
    Console.WriteLine("下载中。。。");
    }
    }

    HttpClient:

    HttpClient是.NET4.5引入的一个HTTP客户端库,其命名空间为 System.Net.Http ,.NET 4.5之前我们可能使用WebClient和HttpWebRequest来达到相同目的。HttpClient利用了最新的面向任务模式,使得处理异步请求非常容易。它适合用于多次请求操作,一般设置好默认头部后,可以进行重复多次的请求,基本上用一个实例可以提交任何的HTTP请求。HttpClient有预热机制,第一次进行访问时比较慢,所以不应该用到HttpClient就new一个出来,应该使用单例或其他方式获取HttpClient的实例

    单例模式:

    单例模式(Singleton Pattern)这种类型的设计模式属于创建型模式,它提供了一种创建对象的最佳方式。

    这种模式涉及到一个单一的类,该类负责创建自己的对象,同时确保只有单个对象被创建。这个类提供了一种访问其唯一的对象的方式,可以直接访问,不需要实例化该类的对象。

    单例创建步骤:1、定义静态私有对象;2、定义私有构造函数;3、提供公共获取对象方法;

    单例模式一般分为两种实现模式:懒汉模式、饿汉模式(以下为Java代码实现)

    懒汉模式:  默认不会实例化,什么时候用什么时候new

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

    这种方式是最基本的实现方式,这种实现最大的问题就是不支持多线程。因为没有加锁 synchronized,所以严格意义上它并不算单例模式。
    这种方式 lazy loading 很明显,不要求线程安全,在多线程不能正常工作。

    饿汉模式:类初始化时,会立即加载该对象,线程天生安全,调用效率高

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

    双检锁/双重校验锁(DCL,即 double-checked locking):这种方式采用双锁机制,安全且在多线程情况下能保持高性能

    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异步请求方法 */
    {
    try
    {
    HttpContent content = new StringContent( strJson );
    content.Headers.ContentType = new System.Net.Http.Headers.MediaTypeHeaderValue( "application/json" );
    /* 由HttpClient发出异步Post请求 */
    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同步请求方法 */
    {
    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发出Post请求
    */
    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有预热机制,第一次请求比较慢;可以通过初始化前发送一次head请求解决:

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

    三者区别列表:

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  • 原文地址:https://www.cnblogs.com/changbaishan/p/13897086.html
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