（二）模拟浏览器抓取网页

第一节：设置请求头消息 User-Agent 模拟浏览器

HttpClient设置请求头消息User-Agent模拟浏览器

用前面的代码：

 1 package com.javaxk.httpclient.chap02;
 2 
 3 import org.apache.http.HttpEntity;
 4 import org.apache.http.client.methods.CloseableHttpResponse;
 5 import org.apache.http.client.methods.HttpGet;
 6 import org.apache.http.impl.client.CloseableHttpClient;
 7 import org.apache.http.impl.client.HttpClients;
 8 import org.apache.http.util.EntityUtils;
 9 
10 public class Demo1 {
11     
12     public static void main(String[] args)throws Exception {
13         CloseableHttpClient httpClient=HttpClients.createDefault(); // 创建httpClient实例
14         HttpGet httpGet=new HttpGet("http://www.tuicool.com/"); // 创建httpget实例
15         CloseableHttpResponse response=httpClient.execute(httpGet); // 执行http get请求
16         HttpEntity entity=response.getEntity(); // 获取返回实体
17         System.out.println("网页内容："+EntityUtils.toString(entity, "utf-8")); // 获取网页内容
18         response.close(); // response关闭
19         httpClient.close(); // httpClient关闭
20     }
21 
22 }

返回内容：

网页内容：<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
</head>
<body>
<p>系统检测亲不是真人行为，因系统资源限制，我们只能拒绝你的请求。如果你有疑问，可以通过微博 http://weibo.com/tuicool2012/ 联系我们。</p>
</body>
</html>

我们模拟下浏览器设置下User-Agent头消息：

加下 httpGet.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0"); // 设置请求头消息User-Agent

 1 package com.javaxk.httpclient.chap02;
 2 
 3 import org.apache.http.HttpEntity;
 4 import org.apache.http.client.methods.CloseableHttpResponse;
 5 import org.apache.http.client.methods.HttpGet;
 6 import org.apache.http.impl.client.CloseableHttpClient;
 7 import org.apache.http.impl.client.HttpClients;
 8 import org.apache.http.util.EntityUtils;
 9 
10 public class Demo1 {
11     
12     public static void main(String[] args)throws Exception {
13         CloseableHttpClient httpClient=HttpClients.createDefault(); // 创建httpClient实例
14         HttpGet httpGet=new HttpGet("http://www.tuicool.com/"); // 创建httpget实例
15         httpGet.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0");    // 设置请求头消息User-Agent
16         CloseableHttpResponse response=httpClient.execute(httpGet); // 执行http get请求
17         HttpEntity entity=response.getEntity(); // 获取返回实体
18         System.out.println("网页内容："+EntityUtils.toString(entity, "utf-8")); // 获取网页内容
19         response.close(); // response关闭
20         httpClient.close(); // httpClient关闭
21     }
22 
23 }

运行：

当然通过火狐firebug，我们还可以看到其他请求头消息：

都是可以通过setHeader方法设置key value；来得到模拟浏览器请求；

第二节：获取响应内容类型 Content-Type

HttpClient获取响应内容类型Content-Type

响应的网页内容都有类型也就是Content-Type

通过火狐firebug，我们看响应头信息：

当然我们可以通过HttpClient接口来获取；

HttpEntity的getContentType().getValue() 就能获取到响应类型；

 1 package com.javaxk.httpclient.chap02;
 2 
 3 import org.apache.http.HttpEntity;
 4 import org.apache.http.client.methods.CloseableHttpResponse;
 5 import org.apache.http.client.methods.HttpGet;
 6 import org.apache.http.impl.client.CloseableHttpClient;
 7 import org.apache.http.impl.client.HttpClients;
 8 import org.apache.http.util.EntityUtils;
 9 
10 public class Demo2 {
11     
12     public static void main(String[] args) throws Exception{
13         CloseableHttpClient httpClient=HttpClients.createDefault(); // 创建httpClient实例
14         HttpGet httpGet=new HttpGet("http://www.javaxk.com"); // 创建httpget实例
15         //HttpGet httpGet=new HttpGet("http://central.maven.org/maven2/HTTPClient/HTTPClient/0.3-3/HTTPClient-0.3-3.jar"); // 创建httpget实例
16         httpGet.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0"); // 设置请求头消息User-Agent
17         CloseableHttpResponse response=httpClient.execute(httpGet); // 执行http get请求
18         HttpEntity entity=response.getEntity(); // 获取返回实体
19         System.out.println("Content-Type:"+entity.getContentType().getValue());
20         //System.out.println("网页内容："+EntityUtils.toString(entity, "utf-8")); // 获取网页内容
21         response.close(); // response关闭
22         httpClient.close(); // httpClient关闭
23     }
24 
25 }

运行输出：

Content-Type:text/html; charset=utf-8

一般网页是text/html当然有些是带编码的，

比如请求www.tuicool.com：输出：

Content-Type:text/html; charset=utf-8

假如请求js文件，比如 http://www.javaxk.com/include/dedeajax2.js

运行输出：

Content-Type:application/javascript

假如请求的是文件，比如 http://central.maven.org/maven2/HTTPClient/HTTPClient/0.3-3/HTTPClient-0.3-3.jar

运行输出：

Content-Type:application/java-archive

当然Content-Type还有一堆，那这东西对于我们爬虫有啥用的，我们再爬取网页的时候，可以通过

Content-Type来提取我们需要爬取的网页或者是爬取的时候，需要过滤掉的一些网页；

第三节：获取响应状态 Status

200 正常
403 拒绝
500 服务器报错
400 未找到页面

HttpClient获取响应状态Status

我们HttpClient向服务器请求时，

正常情况执行成功返回200状态码，

不一定每次都会请求成功，

比如这个请求地址不存在返回404

服务器内部报错返回500

有些服务器有防采集，假如你频繁的采集数据，则返回403 拒绝你请求。

当然我们是有办法的后面会讲到用代理IP。

这个获取状态码，我们可以用 CloseableHttpResponse对象的getStatusLine().getStatusCode()

 1 package com.javaxk.httpclient.chap02;
 2 
 3 import org.apache.http.HttpEntity;
 4 import org.apache.http.client.methods.CloseableHttpResponse;
 5 import org.apache.http.client.methods.HttpGet;
 6 import org.apache.http.impl.client.CloseableHttpClient;
 7 import org.apache.http.impl.client.HttpClients;
 8 import org.apache.http.util.EntityUtils;
 9 
10 public class Demo2 {
11     
12     public static void main(String[] args) throws Exception{
13         CloseableHttpClient httpClient=HttpClients.createDefault(); // 创建httpClient实例
14         HttpGet httpGet=new HttpGet("http://www.javaxk.com"); // 创建httpget实例
15         httpGet.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0"); // 设置请求头消息User-Agent
16         CloseableHttpResponse response=httpClient.execute(httpGet); // 执行http get请求
17         System.out.println("Status:"+response.getStatusLine().getStatusCode());
18         HttpEntity entity=response.getEntity(); // 获取返回实体
19         System.out.println("Content-Type:"+entity.getContentType().getValue());
20         //System.out.println("网页内容："+EntityUtils.toString(entity, "utf-8")); // 获取网页内容
21         response.close(); // response关闭
22         httpClient.close(); // httpClient关闭
23     }
24 
25 }

运行输出：

Status:200

Content-Type:text/html;charset=UTF-8

假如换个页面 http://www.javaxk.com/a.jsp

因为不存在，

所以返回 404

 1 package com.javaxk.httpclient.chap02;
 2 
 3 import org.apache.http.HttpEntity;
 4 import org.apache.http.client.methods.CloseableHttpResponse;
 5 import org.apache.http.client.methods.HttpGet;
 6 import org.apache.http.impl.client.CloseableHttpClient;
 7 import org.apache.http.impl.client.HttpClients;
 8 import org.apache.http.util.EntityUtils;
 9 
10 public class Demo2 {
11     
12     public static void main(String[] args) throws Exception{
13         CloseableHttpClient httpClient=HttpClients.createDefault(); // 创建httpClient实例
14         HttpGet httpGet=new HttpGet("http://www.javaxk.com/a.jsp"); // 创建httpget实例
15         httpGet.setHeader("User-Agent", "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:50.0) Gecko/20100101 Firefox/50.0"); // 设置请求头消息User-Agent
16         CloseableHttpResponse response=httpClient.execute(httpGet); // 执行http get请求
17         System.out.println("Status:"+response.getStatusLine().getStatusCode());
18         HttpEntity entity=response.getEntity(); // 获取返回实体
19         System.out.println("Content-Type:"+entity.getContentType().getValue());
20         //System.out.println("网页内容："+EntityUtils.toString(entity, "utf-8")); // 获取网页内容
21         response.close(); // response关闭
22         httpClient.close(); // httpClient关闭
23     }
24 
25 }

运行输出：

Status:404
Content-Type:text/html