【Java爬虫】005-HttpClient学习笔记（补充：网页内容获取相关）

怼烎@ 2023-10-05 09:06 44阅读 0赞

### 最后更新时间：2020年8月31日11:42:37 ###

# 一、创建HttpClient实例的6种方法 #

package com.zb.crawler.httpclient;
    
    import org.apache.http.client.HttpClient;
    import org.apache.http.impl.client.DefaultHttpClient;
    import org.apache.http.impl.client.HttpClientBuilder;
    import org.apache.http.impl.client.HttpClients;
    
    public class Main {
        public static void main(String[] args) {
            //6种实例化HttpClient的方式
            //第一种方法已过时，不建议使用
            HttpClient httpClient1 = new DefaultHttpClient();
            HttpClient httpClient2 = HttpClients.custom().build();
            HttpClient httpClient3 = HttpClientBuilder.create().build();
            HttpClient httpClient4 = HttpClients.createDefault();
            HttpClient httpClient5 = HttpClients.createSystem();
            HttpClient httpClient6 = HttpClients.createMinimal();
        }
    }

# 二、设置头消息 #

## 1、方式一：一个一个设置 ##

package com.zb.book.httpclient;
    
    import org.apache.http.HttpEntity;
    import org.apache.http.HttpResponse;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.util.EntityUtils;
    
    import java.io.IOException;
    
    public class SetHeaderOne {
        public static void main(String[] args) throws IOException {
            //初始化httpClient
            HttpClient httpClient = HttpClients.custom().build();
            //创建get请求
            HttpGet httpGet = new HttpGet("http://www.baidu.com/");
            //请求头配置
            httpGet.setHeader("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng.*/*;q=0.8");
            httpGet.setHeader("Accept-Encoding","gzip,deflate");
            httpGet.setHeader("Accept-Language","zh-CN,zh;q=0.9");
            httpGet.setHeader("Cache-Control","max-age=0");
            httpGet.setHeader("Host","http://www.baidu.com/");
            httpGet.setHeader("User-Agent","Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36");
            //发出Get请求
            HttpResponse response = httpClient.execute(httpGet);
            //获取响应状态码
            int statusCode = response.getStatusLine().getStatusCode();
            if(statusCode==200) {
                //获取网页内容流
                HttpEntity entity = response.getEntity();
                //转换为字符串形式，需要设置编码
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
                //关闭内容流
                EntityUtils.consume(entity);
            }
        }
    }

## 2、方式二：封装到list集合统一设置 ##

package com.zb.book.httpclient;
    
    import org.apache.http.Header;
    import org.apache.http.HttpEntity;
    import org.apache.http.HttpHeaders;
    import org.apache.http.HttpResponse;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.message.BasicHeader;
    import org.apache.http.util.EntityUtils;
    
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.List;
    
    public class SetHeaderList {
        public static void main(String[] args) throws IOException {
            //通过集合封装头信息
            List<Header> headerList = new ArrayList<>();
            headerList.add(new BasicHeader(HttpHeaders.ACCEPT,"text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng.*/*;q=0.8"));
            headerList.add(new BasicHeader(HttpHeaders.ACCEPT_ENCODING,"gzip,deflate"));
            headerList.add(new BasicHeader(HttpHeaders.ACCEPT_LANGUAGE,"zh-CN,zh;q=0.9"));
            headerList.add(new BasicHeader(HttpHeaders.CACHE_CONTROL,"max-age=0"));
            headerList.add(new BasicHeader(HttpHeaders.HOST,"http://www.baidu.com/"));
            headerList.add(new BasicHeader(HttpHeaders.USER_AGENT,"Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/78.0.3904.108 Safari/537.36"));
            //初始化httpClient
            HttpClient httpClient = HttpClients.custom().setDefaultHeaders(headerList).build();
            //创建get请求
            HttpGet httpGet = new HttpGet("http://www.baidu.com/");
            //发出Get请求
            HttpResponse response = httpClient.execute(httpGet);
            //获取响应状态码
            int statusCode = response.getStatusLine().getStatusCode();
            if(statusCode==200) {
                //获取网页内容流
                HttpEntity entity = response.getEntity();
                //转换为字符串形式，需要设置编码
                String content = EntityUtils.toString(response.getEntity(), "UTF-8");
                System.out.println(content);
                //关闭内容流
                EntityUtils.consume(entity);
            }
        }
    }

## 3、其他方式 ##

非常简单，可参考前两种方式实现；

# 三、POST提交表单 #

package com.zb.book.httpclient;
    
    import org.apache.http.NameValuePair;
    import org.apache.http.client.entity.UrlEncodedFormEntity;
    import org.apache.http.client.methods.HttpPost;
    import org.apache.http.message.BasicNameValuePair;
    
    import java.io.UnsupportedEncodingException;
    import java.util.ArrayList;
    import java.util.List;
    
    //Post提交表单
    public class PostSubmitForm {
        public static void main(String[] args) throws UnsupportedEncodingException {
            //使用list集合存储欲传递参数
            List<NameValuePair> nvps = new ArrayList<>();
            nvps.add(new BasicNameValuePair("param1","value1"));
            nvps.add(new BasicNameValuePair("param2","value2"));
            //创建UrlEncodedFormEntity对象
            UrlEncodedFormEntity entity = new UrlEncodedFormEntity(nvps, "UTF-8");
            //创建HttpPost
            HttpPost httpPost = new HttpPost("http://xxx.xxx.xxx");
            httpPost.setEntity(entity);
            //执行该请求即可实现提交表单
        }
    }

# 四、超时设置 #

## 1、概述 ##

使用HttpClient可设置三种超时时间：RequestTimeout（获取连接超时时间）、ConnectTimeout（建立连接超时时间）、SocketTimeout（获取数据超时时间）。配置这三种超时时间，需要用到HttpClient的RequestConfig类中的方法custom()，该方法返回值为实例化的内部类Builder（配置器），其功能是配置先关请求的字段，还可以设置代理（proxy）、Cookie规范（cookieSpec）、是否允许HTTP相关认证等；

## 2、代码演示 ##

package com.zb.book.httpclient;
    
    import org.apache.http.client.config.RequestConfig;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    
    //设置超时时间
    public class SetTimeout {
        public static void main(String[] args) {
            //创建RequestConfig配置，全部设置为10秒
            RequestConfig requestConfig = RequestConfig.custom()
                    .setSocketTimeout(10000)//SocketTimeout（获取数据超时时间）
                    .setConnectTimeout(10000)//ConnectTimeout（建立连接超时时间）
                    .setConnectionRequestTimeout(1000)//RequestTimeout（获取连接超时时间）
                    .build();
            //配置到httpclient
            CloseableHttpClient httpClient = HttpClients.custom().setDefaultRequestConfig(requestConfig).build();
            //后面进行正常的请求及相关处理即可
            //另外可用请求方法设置配置，其他写法当做适当改变
            //httpGet.setConfig(requestConfig);
        }
    }

# 五、代理服务器的设置 #

package com.zb.book.httpclient;
    
    import org.apache.http.HttpHost;
    import org.apache.http.client.config.RequestConfig;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    
    //设置代理服务器
    public class SetProxy {
        public static void main(String[] args) {
            //创建RequestConfig配置，全部设置为10秒
            RequestConfig requestConfig = RequestConfig.custom()
                    .setProxy(new HttpHost("171.221.239.11",808,null))
                    .build();
            //配置到httpclient
            CloseableHttpClient httpClient = HttpClients.custom().setDefaultRequestConfig(requestConfig).build();
            //后面进行正常的请求及相关处理即可
            //另外可用请求方法设置配置，其他写法当做适当改变
            //httpGet.setConfig(requestConfig);
        }
    }

# 六、文件下载 #

## 1、概述 ##

下载HTML、图片、PDF和压缩包等文件时，一种方法是使用HttpEntity类将响应实体转化为字节数组，再利用输出流的方式写入指定文件。另一种方法是**使用HttpEntity类中的writeTo(OutputStream)方法**，直接将响应实体写入指定的输出流中，**这种方法简单切常用**，代码演示如下。

## 2、代码演示 ##

package com.zb.book.httpclient;
    
    import org.apache.http.HttpEntity;
    import org.apache.http.client.methods.CloseableHttpResponse;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.util.EntityUtils;
    
    import java.io.FileOutputStream;
    import java.io.IOException;
    
    //下载文件
    public class DownloadFile {
        public static void main(String[] args) throws IOException {
            //创建HttpClient对象
            CloseableHttpClient httpClient = HttpClients.custom().build();
            //创建HttpGet对象
            HttpGet httpGet = new HttpGet("https://www.baidu.com/img/PCtm_d9c8750bed0b3c7d089fa7d55720d6cf.png");
            //获取结果
            CloseableHttpResponse response = httpClient.execute(httpGet);
            HttpEntity httpEntity = response.getEntity();
            //写出
            httpEntity.writeTo(new FileOutputStream("C:\\Users\\ZiBo\\Desktop\\1.png"));
            //消耗实体
            EntityUtils.consume(httpEntity);
        }
    }

# 七、HTTPS请求认证 #

## 1、概述 ##

与jsoup类似，具体做法见代码演示；

## 2、代码演示 ##

### SSLClient类： ###

package com.httpclient.ssl;
    
    import java.security.KeyManagementException;
    import java.security.NoSuchAlgorithmException;
    import java.security.cert.X509Certificate;
    import java.util.Arrays;
    import javax.net.ssl.SSLContext;
    import javax.net.ssl.X509TrustManager;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.config.AuthSchemes;
    import org.apache.http.client.config.CookieSpecs;
    import org.apache.http.client.config.RequestConfig;
    import org.apache.http.config.Registry;
    import org.apache.http.config.RegistryBuilder;
    import org.apache.http.conn.socket.ConnectionSocketFactory;
    import org.apache.http.conn.socket.PlainConnectionSocketFactory;
    import org.apache.http.conn.ssl.NoopHostnameVerifier;
    import org.apache.http.conn.ssl.SSLConnectionSocketFactory;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
    public class SSLClient {
    	/**
    	 * 基于SSL配置httpClient
    	 * @param  SSLProtocolVersion(SSL, SSLv3, TLS, TLSv1, TLSv1.1, TLSv1.2)
    	 * @return httpClient
    	 */
    	public HttpClient initSSLClient(String SSLProtocolVersion){
    		RequestConfig defaultConfig = null;  
    		PoolingHttpClientConnectionManager pcm = null;
    		try {
    			X509TrustManager xtm = new SSL509TrustManager(); //创建信任管理
    			//创建SSLContext对象,，并使用指定的信任管理器初始化
    			SSLContext context = SSLContext.getInstance(SSLProtocolVersion);
    			context.init(null, new X509TrustManager[]{xtm}, null);
    			//从SSLContext对象中得到SSLConnectionSocketFactory对象
    			SSLConnectionSocketFactory sslConnectionSocketFactory = new SSLConnectionSocketFactory(context, NoopHostnameVerifier.INSTANCE);
    			/*从SSLContext对象中得到SSLConnectionSocketFactory对象
    			*NoopHostnameVerifier.INSTANCE表示接受接受任何有效的和符合目标主机的SSL会话
    			*/
    			Registry<ConnectionSocketFactory> sfr = RegistryBuilder.<ConnectionSocketFactory>create()
    					.register("http", PlainConnectionSocketFactory.INSTANCE)
    					.register("https", sslConnectionSocketFactory).build();
    			//基于配置创建连接池
    			pcm = new PoolingHttpClientConnectionManager(sfr);
    		}catch(NoSuchAlgorithmException | KeyManagementException e){
    			e.printStackTrace();
    		}
    		//设置全局请求配置,包括Cookie规范,HTTP认证,超时
    		defaultConfig = RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD_STRICT)
    				.setExpectContinueEnabled(true)
    				.setTargetPreferredAuthSchemes(Arrays.asList(AuthSchemes.NTLM, AuthSchemes.DIGEST))
    				.setProxyPreferredAuthSchemes(Arrays.asList(AuthSchemes.BASIC))
    				.setConnectionRequestTimeout(30*1000)
                    .setConnectTimeout(30*1000)
                    .setSocketTimeout(30*1000)
                    .build();
    		//初始化httpclient
    		HttpClient httpClient = HttpClients.custom().setConnectionManager(pcm).setDefaultRequestConfig(defaultConfig)
    				.build();
    		return httpClient;
    	}
    	//实现X509TrustManager接口
    	private static class SSL509TrustManager implements X509TrustManager {
    		//检查客户端证书
    		public void checkClientTrusted(X509Certificate[] x509Certificates, String s) {
    			//do nothing 接受任意客户端证书
    		}
    		//检查服务器端证书  
    		public void checkServerTrusted(X509Certificate[] x509Certificates, String s)  {
    			//do nothing  接受任意服务端证书
    		}
    		//返回受信任的X509证书
    		public X509Certificate[] getAcceptedIssuers() {
    			return new X509Certificate[0];
    		}
    	};
    }

### test类： ###

package com.httpclient.ssl;
    
    import java.io.IOException;
    
    import org.apache.http.HttpResponse;
    import org.apache.http.HttpStatus;
    import org.apache.http.ParseException;
    import org.apache.http.client.HttpClient;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.util.EntityUtils;
    public class Test {
    	public static void main(String[] args) throws ParseException, IOException {
    		String url = "https://cn.kompass.com/a/hospitality-tourism-hotel-and-catering-industries/78/";
    		SSLClient sslClient = new SSLClient();   //实例化
    		HttpClient httpClientSSL = sslClient.initSSLClient("TLS");
    		HttpGet httpGet = new HttpGet(url);
    		//获取结果
    		HttpResponse httpResponse = null;
    		try {
    			httpResponse = httpClientSSL.execute(httpGet);
    		} catch (IOException e) {
    			e.printStackTrace();
    		}
    		if(httpResponse .getStatusLine().getStatusCode() == HttpStatus.SC_OK){ //状态码200表示响应成功
    			//获取实体内容
    			String entity = EntityUtils.toString (httpResponse.getEntity(),"UTF-8");
    			//输出实体内容
    			System.out.println(entity);
    			EntityUtils.consume(httpResponse.getEntity());       //消耗实体
    		}else {
    			//关闭HttpEntity的流实体
    			EntityUtils.consume(httpResponse.getEntity());        //消耗实体
    		}
    	}
    }

# 八、请求重试 #

## 1、概述 ##

使用HtpClient请求URL时，有时会出现请求异常的情况。针对一些非致命的异常，可以通过请求重试解决。HttpClient提供了默认重试策略DefalutHttpRequestRetryHandler。DefalutHttpRequestRetryHandler类实现了HttpRequestRetryHandler接口，重写了retryRequest(方法。由源码可以发现DefalutHttpRequestRetryHandler类定义的默认重试次数为3次；幂等方法(如GET和HEAD是幂等的)可以重试：如果网页请求失败，可以重试。另外，针对4种异常不进行重试，这四种异常分别是InterruptedIOException (线程中断异常)、UnknownHostException (未知的Host异常)、ConnectException (连接异常,如连接拒绝异常)和SSLException ( HTTPS请求认证异常)。

## 2、代码演示 ##

package com.zb.book.httpclient;
    
    import org.apache.http.impl.client.DefaultHttpRequestRetryHandler;
    import org.apache.http.impl.client.HttpClients;
    
    //设置请求重试
    public class SetRequestRetry {
        public static void main(String[] args) {
            //第一种：默认重试3次
            HttpClients.custom()
                    .setRetryHandler(new DefaultHttpRequestRetryHandler())
                    .build();
            //第二种：自定义重试5次
            HttpClients.custom()
                    .setRetryHandler(new DefaultHttpRequestRetryHandler(5,true))
                    .build();
        }
    }

## 3、补充说明 ##

值得注意的是，在进行数据爬取时经常遇到的两种超时时间: ConnectTimeout(建立连接的超时时间)和SocketTimeout(获取数据的超时时间)，这两种超时时间对应的异常( ConnectTimeoutException与SocketTimeoutException )都继承自InterruptedIOException类，即属于线程中断异常，不会进行重试。

# 九、多线程执行请求演示代码摘录 #

（可参考原始学习笔记的连接池）

package com.httpclient.thread;
    import java.io.FileNotFoundException;
    import java.io.FileOutputStream;
    import java.io.IOException;
    import java.io.OutputStream;
    import java.nio.charset.CodingErrorAction;
    import java.util.Arrays;
    import java.util.concurrent.ExecutorService;
    import java.util.concurrent.Executors;
    import org.apache.http.Consts;
    import org.apache.http.client.ClientProtocolException;
    import org.apache.http.client.config.AuthSchemes;
    import org.apache.http.client.config.CookieSpecs;
    import org.apache.http.client.config.RequestConfig;
    import org.apache.http.client.methods.CloseableHttpResponse;
    import org.apache.http.client.methods.HttpGet;
    import org.apache.http.client.protocol.HttpClientContext;
    import org.apache.http.config.ConnectionConfig;
    import org.apache.http.config.SocketConfig;
    import org.apache.http.impl.client.CloseableHttpClient;
    import org.apache.http.impl.client.HttpClients;
    import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
    import org.apache.http.protocol.HttpContext;
    import org.apache.http.util.EntityUtils;
    public class Test {
    	public static void main(String[] args) throws FileNotFoundException {
    		//添加连接参数
    		ConnectionConfig connectionConfig = ConnectionConfig.custom()
    				.setMalformedInputAction(CodingErrorAction.IGNORE)
    				.setUnmappableInputAction(CodingErrorAction.IGNORE)
    				.setCharset(Consts.UTF_8)
    				.build();
    		//添加socket参数
    		SocketConfig socketConfig = SocketConfig.custom()
    				.setTcpNoDelay(true)
    				.build();
    		//配置连接池管理器
    		PoolingHttpClientConnectionManager pcm = new PoolingHttpClientConnectionManager();
    		// 设置最大连接数
    		pcm.setMaxTotal(100);
    		// 设置每个连接的路由数
    		pcm.setDefaultMaxPerRoute(10);
    		//设置连接信息
    		pcm.setDefaultConnectionConfig(connectionConfig);
    		//设置socket信息
    		pcm.setDefaultSocketConfig(socketConfig);
    		//设置全局请求配置,包括Cookie规范,HTTP认证,超时
    		RequestConfig defaultConfig = RequestConfig.custom()
    				.setCookieSpec(CookieSpecs.STANDARD_STRICT)
    				.setExpectContinueEnabled(true)
    				.setTargetPreferredAuthSchemes(Arrays
    						.asList(AuthSchemes.NTLM, AuthSchemes.DIGEST))
    				.setProxyPreferredAuthSchemes(Arrays.asList(AuthSchemes.BASIC))
    				.setConnectionRequestTimeout(30*1000)
    				.setConnectTimeout(30*1000)
    				.setSocketTimeout(30*1000)
    				.build();
    		CloseableHttpClient httpClient = HttpClients.custom()
    				.setConnectionManager(pcm)
    				.setDefaultRequestConfig(defaultConfig)
    				.build();
    		// 请求的URL
    		String[] urlArr = {
    				"https://hbr.org/podcasts",
    				"https://hbr.org/magazine",
    				"https://hbr.org/most-popular",
    				"https://hbr.org/big-ideas",
    				"https://hbr.org/reading-lists"
    		};
    		//创建固定大小的线程池
    		ExecutorService exec = Executors.newFixedThreadPool(3);
    		for(int i = 0; i< urlArr.length;i++){
    			String filename = urlArr[i].split("org/")[1]; //HTML需要输出的文件名
    			//创建HTML文件输出目录
    			OutputStream out = new FileOutputStream("file/" + filename);
    			HttpGet httpget = new HttpGet(urlArr[i]);
    			//启动线程执行请求
    			exec.execute(new DownHtmlFileThread(httpClient, httpget, out));
    		}
    		//关闭线程
    		exec.shutdown();
    	}
    	static class DownHtmlFileThread extends Thread {
    		private final CloseableHttpClient httpClient;
    		private final HttpContext context;
    		private final HttpGet httpget;
    		private final OutputStream out;
    		//输入的参数
    		public DownHtmlFileThread(CloseableHttpClient httpClient, 
    				HttpGet httpget, OutputStream out) {
    			this.httpClient = httpClient;
    			this.context = HttpClientContext.create();
    			this.httpget = httpget;
    			this.out = out;
    		}
    		@Override
    		public void run() {
    			System.out.println(Thread.currentThread().getName() + 
    					"线程请求的URL为:" + httpget.getURI());
    			try {
    				CloseableHttpResponse response = httpClient.execute(
    						httpget, context);  //执行请求
    				try {
    					//HTML文件写入文档
    					out.write(EntityUtils.toString(response.getEntity(),"gbk")
    							.getBytes());
    					out.close();
    					//消耗实体
    					EntityUtils.consume(response.getEntity());
    				} finally{
    					response.close(); //关闭响应
    				}
    			} catch (ClientProtocolException ex) {
    				ex.printStackTrace(); // 处理 protocol错误
    			} catch (IOException ex) {
    				ex.printStackTrace(); // 处理I/O错误
    			}
    		}
    	}
    }