apache HttpClient 学习系列--2 之HttpContext

落日映苍穹つ 2021-06-24 14:37 318阅读 0赞

摘要: 本文主要讲解HttpContext的使用  
首先是一个Servlet用于本次试验。

package com.lu.controller;
    
    import java.io.IOException;
    import java.io.OutputStream;
    import java.io.PrintWriter;
    
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.HttpSession;
    
    @SuppressWarnings("serial")
    public class RirectServlet extends HttpServlet {
    
        public void doGet(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
            this.doPost(request, response);
        }
    
        public void doPost(HttpServletRequest request, HttpServletResponse response)
                throws ServletException, IOException {
    
            request.setCharacterEncoding("UTF-8");
            response.setContentType("text/html;charset=utf-8");
    
            OutputStream out = response.getOutputStream();
            PrintWriter pw = new PrintWriter(out);
    
            // 记录返回的内容
            String returnContent = null;
    
            HttpSession session = request.getSession();
            String user = (String) session.getAttribute("username");
    
            // 如果不为空,说明已登录
            if (user != null) {
                returnContent = "you have been logined, " + user;
            } else {
                // 为空说明未登录,设置username到session中
                String username = request.getParameter("username");
                session.setAttribute("username", username);
                returnContent = "login success";
            }
    
            try {
                pw.println(returnContent);
            } finally {
                pw.close();
                out.close();
            }
        }
    
    }

在本机中访问URI为：http://localhost:8080/spiderweb/RirectServlet  
  
  
下面看请求

package com.lu.test;
    
    import java.util.ArrayList;
    import java.util.List;
    
    import org.apache.http.HttpEntity;
    import org.apache.http.NameValuePair;
    import org.apache.http.client.entity.UrlEncodedFormEntity;
    import org.apache.http.client.methods.CloseableHttpResponse;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.client.protocol.HttpClientContext;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.message.BasicNameValuePair;
    import org.apache.http.protocol.BasicHttpContext;
    import org.apache.http.protocol.HttpContext;
    import org.apache.http.util.EntityUtils;
    
    public class HttpClientTest {
    
        private static HttpContext localContext = new BasicHttpContext();
        private static HttpClientContext context = HttpClientContext
                .adapt(localContext);
    
        public static void main(String[] args) throws Exception {
            CloseableHttpClient httpClient = HttpClients.createDefault();
    
            try {
                // 模拟表单
                List<NameValuePair> params = new ArrayList<NameValuePair>();
                params.add(new BasicNameValuePair("username", "**"));
                UrlEncodedFormEntity entity = new UrlEncodedFormEntity(params,
                        "UTF-8");
                HttpPost httpPost = new HttpPost(
                        "http://localhost:8080/spiderweb/RirectServlet");
                httpPost.setEntity(entity);
    
                // 将HttpClientContext传入execute()中
                CloseableHttpResponse response = httpClient.execute(httpPost,
                        context);
    
                try {
                    HttpEntity responseEntity = response.getEntity();
                    System.out.println(EntityUtils.toString(responseEntity));
    
                } finally {
                    response.close();
                }
            } finally {
                httpClient.close();
            }
    
            CloseableHttpClient httpClient2 = HttpClients.createDefault();
    
            try {
                HttpGet httpGet = new HttpGet(
                        "http://localhost:8080/spiderweb/RirectServlet");
    
                // 设置相同的HttpClientContext
                CloseableHttpResponse response = httpClient2.execute(httpGet,
                        context);
                try {
                    HttpEntity entity = response.getEntity();
                    System.out.println(EntityUtils.toString(entity));
                } finally {
                    response.close();
                }
            } finally {
                httpClient2.close();
            }
    
        }
    }

输出结果为：  
  
  
login success  
you have been logined, \*\*  
  
  
可能大家认为这个结果很正常。第一次登陆了，第二次肯定会输出you have been logined, \*\*。但是大家别忘了，现在不是在浏览器环境下，浏览器会帮你提取服务器传回的sessionId并在你下次请求的时候传给服务器，那么两次请求用的就是同一个session对象，那么自然的就会有上面的输出。  
  
但是现在是在自己写代码访问。我们没有获取sessionId，也没有向服务器传送sessionId，那么两次请求服务器就会为你创建两个sessionId不同的session对象。  
  
那为什么输出结果却是跟浏览器得到的结果一样呢？肯定是什么东西为我们自动完成了获取sessionId传送sessionId的功能。毫无疑问，就是context。 BasicHttpContext里有个Map<Object,Object>的对象用来记录一次请求响应的信息，当响应信息返回时，就会被set到context里，当然响应的cookie信息也就被存储在context里,包括传回的sessionId。  
  
当第二次请求的时候传入相同的context，那么请求的过程中会将context里的sessionId提取出来传给服务器，sessionId一样，自然而然的就是同一个session对象。  
那么大家明白context的作用了吗？  
按照官方教程的说法来说  
  
  
代表一个逻辑相关的会话的多个请求序列应该具有相同的HttpContext实例以确保请求之间的信息状态的自动传播  
  
  
由于初学，不对的地方还望大家指出。