一. 前言
前端调用有Form表单提交，ajax提交，ajax一般是用Jquery的简化写法，在这里不再过多介绍； 后端调用大约有这些：WebCient、WebRequest、Httpclient、WebapiClient，重点探讨Get和Post请求，Put和Delete请求用较少。
下面排着介绍Get和Post的基本写法，最后再封装一下，便于调用。
PS：其中Post请求有两种，分别是： "application/x-www-form-urlencoded"表单提交的方式 和 "application/json" Json格式提交的方式。
(1). Post的表单提交的格式为："userName=admin&pwd=123456"。
(2). Post的Json的提交格式为：将实体(类)转换成json字符串。
下面先编写几个服务器端的接口方法，便于调用。
1 //Get http://localhost:2131/api/Forth/CheckLogin?userName=admin&pwd=123456
2 [HttpGet]
3 public string CheckLogin(string userName, string pwd)
4 {
5 if (userName == "admin" && pwd == "123456")
6 {
7 return "ok";
8 }
9 else
10 {
11 return "error";
12 }
13 }
14
15
16 //Post http://localhost:2131/api/Forth/Register
17 [HttpPost]
18 public string Register([FromBody]LoginModel model)
19 {
20 if (model.userName == "admin" && model.pwd == "123456")
21 {
22 return "ok";
23 }
24 else
25 {
26 return "error";
27 }
28 }
29
30 //Post http://localhost:2131/api/Forth/Register2
31 [HttpPost]
32 public string Register2([FromBody]dynamic model)
33 {
34 if (model.userName == "admin" && model.pwd == "123456")
35 {
36 return "ok";
37 }
38 else
39 {
40 return "error";
41 }
42 }
为了方便下面的测试，给上述三个地址进行命名描述和序列化方法的初始化
二. WebClient
1. Get请求
1 WebClient wc = new WebClient(); 2 string url = url1; 3 wc.Encoding = Encoding.UTF8; 4 string result = wc.DownloadString(url); 5 Console.WriteLine(result); 6 Console.ReadKey();
2. Post的表单提交方式（url2能访问，url3报500错误）
1 WebClient wc = new WebClient();
2 string url = url3;
3 wc.Encoding = Encoding.UTF8;
4 //也可以向表头中添加一些其他东西
5 wc.Headers.Add("Content-Type", "application/x-www-form-urlencoded");
6 string result = wc.UploadString(url, "userName=admin&pwd=123456");
7 Console.WriteLine(result);
8 Console.ReadKey();
3. Post的JSON提交格式(url2和url3都能正常访问)
1 var user = new
2 {
3 userName = "admin",
4 pwd = "123456"
5 };
6 WebClient wc = new WebClient();
7 string url = url3;
8 wc.Encoding = Encoding.UTF8;
9 wc.Headers.Add("Content-Type", "application/json");
10 string result = wc.UploadString(url, jss.Serialize(user));
11 Console.WriteLine(result);
12 Console.ReadKey();
三. WebRequest
1. Get请求
1 HttpWebRequest request = (HttpWebRequest)WebRequest.Create(url1);
2 request.Timeout = 30 * 1000;
3 request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.118 Safari/537.36";
4 request.ContentType = "application/x-www-form-urlencoded; charset=UTF-8";
5 string result = "";
6 using (var res = request.GetResponse() as HttpWebResponse)
7 {
8 if (res.StatusCode == HttpStatusCode.OK)
9 {
10 StreamReader reader = new StreamReader(res.GetResponseStream(), Encoding.UTF8);
11 result = reader.ReadToEnd();
12 }
13 }
14 Console.WriteLine(result);
15 Console.ReadKey();
2. Post的表单提交方式（url2能访问，url3报500错误）
1 var postData = "userName=admin&pwd=123456";
2 var request = HttpWebRequest.Create(url2) as HttpWebRequest;
3 request.Timeout = 30 * 1000;//设置30s的超时
4 request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.118 Safari/537.36";
5 request.ContentType = "application/x-www-form-urlencoded";
6 request.Method = "POST";
7 byte[] data = Encoding.UTF8.GetBytes(postData);
8 request.ContentLength = data.Length;
9 Stream postStream = request.GetRequestStream();
10 postStream.Write(data, 0, data.Length);
11 postStream.Close();
12 string result = "";
13 using (var res = request.GetResponse() as HttpWebResponse)
14 {
15 if (res.StatusCode == HttpStatusCode.OK)
16 {
17 StreamReader reader = new StreamReader(res.GetResponseStream(), Encoding.UTF8);
18 result = reader.ReadToEnd();
19 }
20 }
21 Console.WriteLine(result);
22 Console.ReadKey();
3. Post的JSON提交格式(url2和url3都能正常访问)
1 var user = new
2 {
3 userName = "admin",
4 pwd = "123456"
5 };
6 var postData = jss.Serialize(user);
7 var request = HttpWebRequest.Create(url2) as HttpWebRequest;
8 request.Timeout = 30 * 1000; //设置30s的超时
9 request.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.118 Safari/537.36";
10 request.ContentType = "application/json";
11 request.Method = "POST";
12 byte[] data = Encoding.UTF8.GetBytes(postData);
13 request.ContentLength = data.Length;
14 Stream postStream = request.GetRequestStream();
15 postStream.Write(data, 0, data.Length);
16 postStream.Close();
17 string result = "";
18 using (var res = request.GetResponse() as HttpWebResponse)
19 {
20 if (res.StatusCode == HttpStatusCode.OK)
21 {
22 StreamReader reader = new StreamReader(res.GetResponseStream(), Encoding.UTF8);
23 result = reader.ReadToEnd();
24 }
25 }
26 Console.WriteLine(result);
27 Console.ReadKey();
四. HttpClient
1. Get请求
1 var handler = new HttpClientHandler();
2 using (var http = new HttpClient(handler))
3 {
4 var response = http.GetAsync(url1).Result;
5 //获取Http的状态值
6 //Console.WriteLine(response.StatusCode);
7 string result = response.Content.ReadAsStringAsync().Result;
8 Console.WriteLine(result);
9 Console.ReadKey();
10 }
2. Post的表单提交方式（url2能访问，url3报500错误）
1 var handler = new HttpClientHandler();
2 using (var http = new HttpClient(handler))
3 {
4 var content = new StringContent("userName=admin&pwd=123456", Encoding.UTF8, "application/x-www-form-urlencoded");
5 var response = http.PostAsync(url2, content).Result;
6 //获取Http的状态值
7 //Console.WriteLine(response.StatusCode);
8 string result = response.Content.ReadAsStringAsync().Result;
9 Console.WriteLine(result);
10 Console.ReadKey();
11 }
3. Post的JSON提交格式(url2和url3都能正常访问)
1 var user = new
2 {
3 userName = "admin",
4 pwd = "123456"
5 };
6 var handler = new HttpClientHandler();
7 using (var http = new HttpClient(handler))
8 {
9 var content = new StringContent(jss.Serialize(user), Encoding.UTF8, "application/json");
10 var response = http.PostAsync(url3, content).Result;
11 //获取Http的状态值
12 //Console.WriteLine(response.StatusCode);
13 string result = response.Content.ReadAsStringAsync().Result;
14 Console.WriteLine(result);
15 Console.ReadKey();
16 }
注：以上代码均是官方的给出的标准写法，但存在很严重的问题，当请求量大的时候，会存在不能释放的问题，解决方案见下面。
解决方案：
将HttpClient做成单例的，不用Using，全局只有一个，来解决tcp连接不能释放的问题。
1 /// <summary>
2 /// 将HttpClient做成单例的，不用Using，全局只有一个
3 /// 来解决tcp连接不能释放的问题
4 /// </summary>
5 public class HttpClientFactory
6 {
7 private static HttpClient _httpClient = null;
8
9 /// <summary>
10 /// 静态的构造函数：只能有一个，且是无参数的
11 /// 由CLR保证，只有在程序第一次使用该类之前被调用，而且只能调用一次
12 /// 说明： keep-alive关键字可以理解为一个长链接，超时时间也可以在上面进行设置，例如10秒的超时时间，当然并发量太大，这个10秒应该会抛弃很多请求
13 /// 发送请求的代码没有了using，即这个httpclient不会被手动dispose，而是由系统控制它，当然你的程序重启时，这也就被回收了。
14 /// </summary>
15 static HttpClientFactory()
16 {
17 _httpClient = new HttpClient(new HttpClientHandler());
18 _httpClient.Timeout = new TimeSpan(0, 0, 10);
19 _httpClient.DefaultRequestHeaders.Connection.Add("keep-alive");
20 }
21
22 /// <summary>
23 /// 对外开放接口
24 /// </summary>
25 /// <returns></returns>
26 public static HttpClient GetHttpClient()
27 {
28 return _httpClient;
29 }
30 }
优化后调用进行Get和Post请求，代码如下
1 var http = HttpClientFactory.GetHttpClient();
2 //1.Get请求
3 var response1 = http.GetAsync(url1).Result;
4 var result1 = response1.Content.ReadAsStringAsync().Result;
5 Console.WriteLine($"Get请求的返回值为：{result1}");
6 //2. Post请求【application/x-www-form-urlencoded】
7 var content2 = new StringContent("userName=admin&pwd=123456", Encoding.UTF8, "application/x-www-form-urlencoded");
8 var response2 = http.PostAsync(url2, content2).Result;
9 string result2 = response2.Content.ReadAsStringAsync().Result;
10 Console.WriteLine($"Post请求【application/x-www-form-urlencoded】的返回值为：{result2}");
11 //3. Post请求 【application/json】
12 var user = new
13 {
14 userName = "admin",
15 pwd = "123456"
16 };
17 var content3 = new StringContent(jss.Serialize(user), Encoding.UTF8, "application/json");
18 var response3 = http.PostAsync(url3, content3).Result;
19 string result3 = response3.Content.ReadAsStringAsync().Result;
20 Console.WriteLine($"Post请求【application/json】的返回值为：{result3}");
21 Console.ReadKey();
五. 扩展
将WebClient、WebRequest、HttpClient三个类进行封装，其中HttpClient做成单例的，便于我们调用。
封装后的调用：
1 var user = new
2 {
3 userName = "admin",
4 pwd = "123456"
5 };
6 // WebClient的相关测试
7 {
8 Console.WriteLine("1.WebClient的相关测试");
9 var result1 = RequestWaysHelp.WcGet(url1);
10 Console.WriteLine(result1);
11 var result2 = RequestWaysHelp.WcPost1(url2, "userName=admin&pwd=123456");
12 Console.WriteLine(result2);
13 var result3 = RequestWaysHelp.WcPost2(url3, user);
14 Console.WriteLine(result3);
15 }
16 // HttpWebRequest的相关测试
17 {
18 Console.WriteLine("2.HttpWebRequest的相关测试");
19 var result1 = RequestWaysHelp.HwGet(url1);
20 Console.WriteLine(result1);
21 var result2 = RequestWaysHelp.HwPost1(url2, "userName=admin&pwd=123456");
22 Console.WriteLine(result2);
23 var result3 = RequestWaysHelp.HwPost2(url3, user);
24 Console.WriteLine(result3);
25 }
26 // HttpClient的相关测试
27 {
28 Console.WriteLine("3.HttpClient的相关测试");
29 var result1 = RequestWaysHelp.HcGet(url1);
30 Console.WriteLine(result1);
31 var result2 = RequestWaysHelp.HcPost1(url2, "userName=admin&pwd=123456");
32 Console.WriteLine(result2);
33 var result3 = RequestWaysHelp.HcPost2(url3, user);
34 Console.WriteLine(result3);
35 }