【Java爬虫】006-URLConnection与HttpURLConnection（网页内容获取）

曾经终败给现在 2023-10-05 09:08 16阅读 0赞

### 最后更新：2020年8月31日11:42:00 ###

# 一、概述 #

URLConnection是java.net包中的一个抽象类，其主要用于实现应用程序与URL之间的通信；

HttpURLConnection继承自URLConnection，也是抽象类；

在网络爬虫中，可以使用URLConnection或HttpURLConnection请求URL获取流数据，通过对流数据的操作，获取具体的实体内容；

# 二、实例化 #

## 1、说明 ##

URLConnection与HttpURLConnection都是抽象类，无法直接创建实例化对象，但可以通过java.net包URL类中的openConnection()方法创建URLConnection与HttpURLConnection实例；

## 2、代码示例 ##

package com.zb.book.connection;
    
    import java.io.IOException;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.net.URLConnection;
    
    public class Main {
        public static void main(String[] args) throws IOException {
            URL url = new URL("http://www.baidu.com/");
            URLConnection urlConnection = url.openConnection();
            HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
        }
    }

# 三、通过GET请求获取响应体html #

package com.zb.book.connection;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.nio.charset.StandardCharsets;
    
    public class Main {
        public static void main(String[] args) throws IOException {
            //创建URL
            URL url = new URL("http://www.baidu.com/");
            //创建连接
            HttpURLConnection connection = (HttpURLConnection)url.openConnection();
            //允许input
            connection.setDoInput(true);
            //设置请求方法是GET
            connection.setRequestMethod("GET");
            //进行连接操作
            connection.connect();
            //如果响应码等于200
            if(HttpURLConnection.HTTP_OK == connection.getResponseCode()){
                //创建BufferedReader输入流来读取URL的响应，并设置编码
                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8));
                //读取内容
                String readLine;
                StringBuilder response = new StringBuilder();
                while (null != (readLine = bufferedReader.readLine())){
                    response.append(readLine);
                }
                bufferedReader.close();
                System.out.println(response.toString());
            }
        }
    }

# 四、模拟提交表单（POST请求） #

package com.zb.book.connection;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.nio.charset.StandardCharsets;
    
    //模拟提交表单（POST请求）
    public class PostSubmitForm {
        public static void main(String[] args) throws IOException {
            //初始化提交表单的参数
            String wen = "EH629625211CS";
            String action = "ajax";
            //初始化URL
            URL url = new URL("http:www.***.com/ems.php");
            //创建连接
            HttpURLConnection connection = (HttpURLConnection)url.openConnection();
            //允许Output
            connection.setDoOutput(true);
            connection.setRequestMethod("POST");
            //拼接请求参数
            byte[] bytes = ("wen" + "=" + wen + "&" + "action" + "=" + action).getBytes();
            //在连接中添加参数
            connection.getOutputStream().write(bytes);
            //定义BufferedReader输入流来读取URL的响应，这里设置编码
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(connection.getInputStream(), StandardCharsets.UTF_8));
            String line;
            StringBuilder html= new StringBuilder();
            while ((line = bufferedReader.readLine()) != null){
                html.append(line);
            }
            System.out.println(html.toString());
            bufferedReader.close();
        }
    }

# 五、设置头消息 #

package com.zb.book.connection;
    
    import java.io.IOException;
    import java.net.URL;
    import java.net.URLConnection;
    
    //设置头信息
    public class SetHeader {
        public static void main(String[] args) throws IOException {
            //初始化URL
            URL url = new URL("http://www.***.com.cn/b.asp");
            URLConnection connection = url.openConnection();
            //HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            //添加请求头信息
            connection.setRequestProperty("Accept", "text/html");
            connection.setRequestProperty("Accept-Language","zh-CN,zh;q=0.5");
            connection.setRequestProperty("Host","www.***.com.cn");
            connection.setRequestProperty("Cache-Control","max-age=0");
            connection.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36");
            connection.connect();
            //其后进行其他操作即可
        }
    }

# 六、连接超时设置 #

## 1、概述 ##

使用URLConnection或HttpURLConnection时，可以设置两种超时时间，分别是连接超时时间（ConnectTimeout）和读取超时时间（ReadTimeout）；

## 2、代码演示 ##

package com.zb.book.connection;
    
    import java.io.IOException;
    import java.net.URL;
    import java.net.URLConnection;
    
    //设置超时时间
    public class SetTimeout {
        public static void main(String[] args) throws IOException {
            //初始化URL
            URL url = new URL("http://www.***.com.cn/b.asp");
            URLConnection connection = url.openConnection();
            //HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
            //设置超时时间
            connection.setConnectTimeout(10000);//连接超时
            connection.setReadTimeout(10000);//读取超时
            //后续可进行其他操作
        }
    }

# 七、代理服务器的使用 #

package com.zb.book.connection;
    
    import java.io.IOException;
    import java.net.InetSocketAddress;
    import java.net.Proxy;
    import java.net.URL;
    import java.net.URLConnection;
    
    //代理服务器的设置
    public class SetProxy {
        public static void main(String[] args) throws IOException {
            //创建代理对象
            Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("171.97.67.160", 3128));
            //初始化URL
            URL url = new URL("http://www.***.com.cn/b.asp");
            //创建连接对象并设置代理
            URLConnection connection = url.openConnection(proxy);
            //建立连接
            connection.connect();
        }
    }

# 八、HTTPS请求认证 #

package com.crawler;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    import java.net.HttpURLConnection;
    import java.net.URL;
    import java.security.cert.X509Certificate;
    import javax.net.ssl.HttpsURLConnection;
    import javax.net.ssl.SSLContext;
    import javax.net.ssl.SSLSocketFactory;
    import javax.net.ssl.TrustManager;
    import javax.net.ssl.X509TrustManager;
    public class URLConnectionSSL {
    	public static void main(String[] args) throws IOException {
    		initUnSecureTSL();
    		//使用URLConnection请求数据
    		URL url = new URL("https://cn.kompass.com/a/hospitality-tourism-hotel-and-catering-industries/78/");
    		HttpURLConnection conn = (HttpURLConnection) url.openConnection();
    				int statusCode = conn.getResponseCode(); //获取响应状态码
    		String responseBody = null;
    		//如果响应状态码为200
    		if (HttpURLConnection.HTTP_OK == statusCode) {  
    			// 定义BufferedReader输入流来读取URL的响应 ,这里设置编码
    			BufferedReader bufferedReader = new BufferedReader(
    					new InputStreamReader(conn.getInputStream(), "utf-8"));  
    			//读取内容
    			String readLine = null;
    			StringBuffer response = new StringBuffer();
    			while (null != (readLine = bufferedReader.readLine())) {
    				response.append(readLine);
    			}
    
    			bufferedReader.close();
    			responseBody = response.toString();
    		}
    		System.out.println(responseBody);
    	}
    	private static void initUnSecureTSL()  {
    		// 创建信任管理器(不验证证书)
    		final TrustManager[] trustAllCerts = new TrustManager[]{new X509TrustManager() {
    			//检查客户端证书
    			public void checkClientTrusted(final X509Certificate[] chain, final String authType) {
    				//do nothing 接受任意客户端证书
    			}
    			//检查服务器端证书
    			public void checkServerTrusted(final X509Certificate[] chain, final String authType) {
    				//do nothing  接受任意服务器端证书
    			}
    			//返回受信任的X509证书
    			public X509Certificate[] getAcceptedIssuers() {
    				return null; //或者return new X509Certificate[0];
    			}
    		}};
    		try {
    			// 创建SSLContext对象,并使用指定的信任管理器初始化
    			SSLContext sslContext = SSLContext.getInstance("SSL");
    			sslContext.init(null, trustAllCerts, new java.security.SecureRandom());
    			// 基于信任管理器创建套接字工厂 (ssl socket factory)
    			SSLSocketFactory sslSocketFactory = sslContext.getSocketFactory();
    			//为HttpsURLConnection配置套接字工厂SSLSocketFactory
    			HttpsURLConnection.setDefaultSSLSocketFactory(sslSocketFactory);
    			//正常访问Https协议网站
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    }