apache HttpClient 学习系列--2 之HttpContext

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。