apache HttpClient 学习系列--2 之HttpContext
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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
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