C#爬虫基础之HttpClient获取HTTP请求与响应

一、概述

Net4.5以上的提供基本类，用于发送 HTTP 请求和接收来自通过 URI 确认的资源的 HTTP 响应。

HttpClient是一个高级 API，用于包装其运行的每个平台上可用的较低级别功能。

// HttpClient is intended to be instantiated once per application, rather than per-use. See Remarks.
static readonly HttpClient client = new HttpClient();

static async Task Main()
{
  // Call asynchronous network methods in a try/catch block to handle exceptions.
  try
  {
     HttpResponseMessage response = await client.GetAsync("http://www.contoso.com/");
     response.EnsureSuccessStatusCode();
     string responseBody = await response.Content.ReadAsStringAsync();
     // Above three lines can be replaced with new helper method below
     // string responseBody = await client.GetStringAsync(uri);

     Console.WriteLine(responseBody);
  }
  catch(HttpRequestException e)
  {
     Console.WriteLine("\nException Caught!");
     Console.WriteLine("Message :{0} ",e.Message);
  }
}

二、HttpClient的使用

1.使用HttpClient调用Oauth的授权接口获取access_token

1）OAuth使用的密码式

2）获取到access_token后才进行下一步

2.带着access_token调用接口

1）hearder上添加bearer方式的access_token

2）调用接口确保成功获取到返回的结果

try
{
    string host = ConfigurationManager.AppSettings["api_host"];
    string username = ConfigurationManager.AppSettings["api_username"];
    string password = ConfigurationManager.AppSettings["api_password"];

    HttpClient httpClient = new HttpClient();

    // 设置请求头信息
    httpClient.DefaultRequestHeaders.Add("Host", host);
    httpClient.DefaultRequestHeaders.Add("Method", "Post");
    httpClient.DefaultRequestHeaders.Add("KeepAlive", "false");   // HTTP KeepAlive设为false，防止HTTP连接保持
    httpClient.DefaultRequestHeaders.Add("UserAgent","Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.11 (KHTML, like Gecko) Chrome/23.0.1271.95 Safari/537.11");

    //获取token
    var tokenResponse = httpClient.PostAsync("http://" + host + "/token", new FormUrlEncodedContent(new Dictionary<string, string> {
                {"grant_type","password"},
                {"username", username},
                {"password", password}
            }));
    tokenResponse.Wait();
    tokenResponse.Result.EnsureSuccessStatusCode();
    var tokenRes = tokenResponse.Result.Content.ReadAsStringAsync();
    tokenRes.Wait();
    var token = Newtonsoft.Json.Linq.JObject.Parse(tokenRes.Result);
    var access_token = token["access_token"].ToString();

    // 调用接口发起POST请求
    var authenticationHeaderValue = new AuthenticationHeaderValue("bearer", access_token);
    httpClient.DefaultRequestHeaders.Authorization = authenticationHeaderValue;
var content = new StringContent(parameter);
    content.Headers.ContentType = new MediaTypeHeaderValue("application/json");
    var response = httpClient.PostAsync("http://" + host + "/" + api_address, content);

    response.Wait();
    response.Result.EnsureSuccessStatusCode();
    var res = response.Result.Content.ReadAsStringAsync();
    res.Wait();return Newtonsoft.Json.JsonConvert.DeserializeObject(res.Result);
}
catch (Exception ex)
{

    return ResultEx.Init(ex.Message);
}

HttpClient 获取图片并保存到本机

class Program
{
    static void Main()
    {
        //图片路径：https://img.infinitynewtab.com/wallpaper/1.jpg
        string imgSourceURL = "https://img.infinitynewtab.com/wallpaper/";
        DownloadImags(imgSourceURL).Wait();
    }
    private static async Task DownloadImags(string url)
    {
        var client = new HttpClient();
        System.IO.FileStream fs;
        int a = 1;
        //文件名：序号+.jpg。可指定范围，以下是获取100.jpg~500.jpg.
        for (int i = 100; i <= 500; i++)
        {
            var uri = new Uri(Uri.EscapeUriString(url+i.ToString()+".jpg"));
            byte[] urlContents = await client.GetByteArrayAsync(uri);
            fs = new System.IO.FileStream(AppDomain.CurrentDomain.BaseDirectory + "\\images\\"+ i.ToString() + ".jpg",System.IO.FileMode.CreateNew);
            fs.Write(urlContents, 0, urlContents.Length);
            Console.WriteLine(a++);
        }
    }
}

以下为封装的类库

using Newtonsoft.Json;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Net;
using System.Net.Http;
using System.Net.Http.Headers;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;

public class HttpClientHelpClass
{
    ///
    /// get请求
    ///
    ///
    ///
    public static string GetResponse(string url, out string statusCode)
    {
        if (url.StartsWith("https"))
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        var httpClient = new HttpClient();
        httpClient.DefaultRequestHeaders.Accept.Add(      new MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = httpClient.GetAsync(url).Result;
        statusCode = response.StatusCode.ToString();
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }
        return null;
    }

    public static string RestfulGet(string url)
    {
        HttpWebRequest request = WebRequest.Create(url) as HttpWebRequest;
        // Get response
        using (HttpWebResponse response = request.GetResponse() as HttpWebResponse)
        {
            // Get the response stream
            StreamReader reader = new StreamReader(response.GetResponseStream());
            // Console application output
            return reader.ReadToEnd();
        }
    }

    public static T GetResponse(string url)
       where T : class, new()
    {
        if (url.StartsWith("https"))
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

       var httpClient = new HttpClient();
        httpClient.DefaultRequestHeaders.Accept.Add(   new MediaTypeWithQualityHeaderValue("application/json"));
        HttpResponseMessage response = httpClient.GetAsync(url).Result;

        T result = default(T);

        if (response.IsSuccessStatusCode)
        {
            Task<string> t = response.Content.ReadAsStringAsync();
            string s = t.Result;

            result = JsonConvert.DeserializeObject(s);
        }
        return result;
    }

    ///
    /// post请求
    ///
    ///
    /// post数据
    ///
    public static string PostResponse(string url, string postData, out string statusCode)
    {
        if (url.StartsWith("https"))
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        HttpContent httpContent = new StringContent(postData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        httpContent.Headers.ContentType.CharSet = "utf-8";

        HttpClient httpClient = new HttpClient();
        //httpClient..setParameter(HttpMethodParams.HTTP_CONTENT_CHARSET, "utf-8");

        HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;

        statusCode = response.StatusCode.ToString();
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }

        return null;
    }

    ///
    /// 发起post请求
    ///
    ///
    /// url
    /// post数据
    ///
    public static T PostResponse(string url, string postData)
        where T : class, new()
    {
        if (url.StartsWith("https"))
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        HttpContent httpContent = new StringContent(postData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        HttpClient httpClient = new HttpClient();

        T result = default(T);

        HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;

        if (response.IsSuccessStatusCode)
        {
            Task<string> t = response.Content.ReadAsStringAsync();
            string s = t.Result;

            result = JsonConvert.DeserializeObject(s);
        }
        return result;
    }

    ///
    /// 反序列化Xml
    ///
    ///
    ///
    ///
    public static T XmlDeserialize(string xmlString)
        where T : class, new()
    {
        try
        {
            XmlSerializer ser = new XmlSerializer(typeof(T));
            using (StringReader reader = new StringReader(xmlString))
            {
                return (T)ser.Deserialize(reader);
            }
        }
        catch (Exception ex)
        {
            throw new Exception("XmlDeserialize发生异常：xmlString:" + xmlString + "异常信息：" + ex.Message);
        }

    }

    public static string PostResponse(string url, string postData, string token, string appId, string serviceURL, out string statusCode)
    {
        if (url.StartsWith("https"))
            System.Net.ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        HttpContent httpContent = new StringContent(postData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/json");
        httpContent.Headers.ContentType.CharSet = "utf-8";

        httpContent.Headers.Add("token", token);
        httpContent.Headers.Add("appId", appId);
        httpContent.Headers.Add("serviceURL", serviceURL);

        HttpClient httpClient = new HttpClient();
        //httpClient..setParameter(HttpMethodParams.HTTP_CONTENT_CHARSET, "utf-8");

        HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;

        statusCode = response.StatusCode.ToString();
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }

        return null;
    }

    ///
    /// 修改API
    ///
    ///
    ///
    ///
    public static string KongPatchResponse(string url, string postData)
    {
        var httpWebRequest = (HttpWebRequest)WebRequest.Create(url);
        httpWebRequest.ContentType = "application/x-www-form-urlencoded";
        httpWebRequest.Method = "PATCH";

        byte[] btBodys = Encoding.UTF8.GetBytes(postData);
        httpWebRequest.ContentLength = btBodys.Length;
        httpWebRequest.GetRequestStream().Write(btBodys, 0, btBodys.Length);

        HttpWebResponse httpWebResponse = (HttpWebResponse)httpWebRequest.GetResponse();
        var streamReader = new StreamReader(httpWebResponse.GetResponseStream());
        string responseContent = streamReader.ReadToEnd();

        httpWebResponse.Close();
        streamReader.Close();
        httpWebRequest.Abort();
        httpWebResponse.Close();

        return responseContent;
    }

    ///
    /// 创建API
    ///
    ///
    ///
    ///
    public static string KongAddResponse(string url, string postData)
    {
        if (url.StartsWith("https"))
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;
        HttpContent httpContent = new StringContent(postData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded") { CharSet = "utf-8" };
        var httpClient = new HttpClient();
        HttpResponseMessage response = httpClient.PostAsync(url, httpContent).Result;
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }
        return null;
    }

    ///
    /// 删除API
    ///
    ///
    ///
    public static bool KongDeleteResponse(string url)
    {
        if (url.StartsWith("https"))
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        var httpClient = new HttpClient();
        HttpResponseMessage response = httpClient.DeleteAsync(url).Result;
        return response.IsSuccessStatusCode;
    }

    ///
    /// 修改或者更改API    
    ///
    ///
    ///
    ///
    public static string KongPutResponse(string url, string postData)
    {
        if (url.StartsWith("https"))
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

        HttpContent httpContent = new StringContent(postData);
        httpContent.Headers.ContentType = new MediaTypeHeaderValue("application/x-www-form-urlencoded") { CharSet = "utf-8" };

        var httpClient = new HttpClient();
        HttpResponseMessage response = httpClient.PutAsync(url, httpContent).Result;
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }
        return null;
    }

    ///
    /// 检索API
    ///
    ///
    ///
    public static string KongSerchResponse(string url)
    {
        if (url.StartsWith("https"))
            ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls;

       var httpClient = new HttpClient();
        HttpResponseMessage response = httpClient.GetAsync(url).Result;
        if (response.IsSuccessStatusCode)
        {
            string result = response.Content.ReadAsStringAsync().Result;
            return result;
        }
        return null;
    }
}

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