HttpClient4.5简单使用

转自：https://www.cnblogs.com/codingexperience/p/5319850.html

一、HttpClient简介

    HttpClient是一个客户端的HTTP通信实现库，它不是一个浏览器。关于HTTP协议，可以搜索相关的资料。它设计的目的是发送与接收HTTP报文。它不会执行嵌入在页面中JavaScript代码，所以当需要抓取通过AJAX技术获取实际内容的页面时需要使用WebClient等其他开源库。HttpClient最新版已经到第5版，但已经稳定的应该是4.5.2版本，官方网址：http://hc.apache.org/。

二、HttpClient简单使用

    HttpClient的主要用途是接收HTTP响应的内容，下面介绍HttpClient的简单使用，抓取博客园的首页。至于HttpClient4.5的常用API可以参考这篇文章：http://liangbizhi.github.io/httpclient-4-3-x-chapter-1/。

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package com.httpclient.demo;   import java.io.IOException; import java.nio.charset.Charset; import java.util.regex.Matcher; import java.util.regex.Pattern;   import org.apache.http.HttpEntity; import org.apache.http.HttpStatus; import org.apache.http.client.ClientProtocolException; import org.apache.http.client.methods.CloseableHttpResponse; import org.apache.http.client.methods.HttpGet; import org.apache.http.entity.ContentType; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import org.apache.http.util.EntityUtils;   public class SimpleHttpClient {    // 使用HttpClient获取博客园首页    public static void main(String[] args) throws ClientProtocolException, IOException {      String targetUrl = "http://www.cnblogs.com/" ;            // 1.建立HttpClient对象      CloseableHttpClient client = HttpClients.createDefault();        // 2.建立Get请求      HttpGet get = new HttpGet(targetUrl);        // 3.发送Get请求      CloseableHttpResponse res = client.execute(get);        // 4.处理请求结果      if (res.getStatusLine().getStatusCode() == HttpStatus.SC_OK) {        HttpEntity entity = res.getEntity();        ContentType contentType = ContentType.getOrDefault(entity);        Charset charset = contentType.getCharset();        String mimeType = contentType.getMimeType();        // 获取字节数组        byte [] content = EntityUtils.toByteArray(entity);        if (charset == null ) {          // 默认编码转成字符串          String temp = new String(content);          String regEx = "(?=<meta).*?(?<=charset=[\\'|\\\"]?)([[a-z]|[A-Z]|[0-9]|-]*)" ;          Pattern p = Pattern.compile(regEx, Pattern.CASE_INSENSITIVE);          Matcher m = p.matcher(temp);          if (m.find() && m.groupCount() == 1 ) {            charset = Charset.forName(m.group( 1 ));          } else {            charset = Charset.forName( "ISO-8859-1" );          }        }        System.out.println( new String(content, charset));      }      }   }

　　

三、HttpClient模拟登陆

     HTTP协议本来是无状态的，但为了保持会话的状态，使用Cookie保存Session信息，当向服务器发送请求时会附加一些会话信息，从而能区分不同会话的状态。用户登陆过程，其实简单而言，就是首先验证用户名与密码，然后服务器生成会话信息保存到本地，最后用户凭借会话信息能够访问类似用户信息等需登陆的网页。

    HttpClient4.5通过CookieStore保存用户的会话信息，还提供HttpClientContext保存用户连接的信息。下面是一个使用HttpClient模拟知乎登陆的简单案例。

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package com.httpclient.demo;   import java.io.IOException; import java.util.LinkedList; import java.util.List;   import org.apache.http.Consts; import org.apache.http.NameValuePair; import org.apache.http.client.CookieStore; import org.apache.http.client.config.CookieSpecs; import org.apache.http.client.config.RequestConfig; 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.cookie.Cookie; import org.apache.http.impl.client.BasicCookieStore; import org.apache.http.impl.client.CloseableHttpClient; import org.apache.http.impl.client.HttpClients; import org.apache.http.message.BasicNameValuePair; import org.apache.http.util.EntityUtils;   /**   * 模拟登陆知乎   */ public class ZhiHuTest {      public static void main(String[] args) throws java.text.ParseException {      String name = "username" ;      String password = "password"            // 全局请求设置      RequestConfig globalConfig = RequestConfig.custom().setCookieSpec(CookieSpecs.STANDARD).build();      // 创建cookie store的本地实例      CookieStore cookieStore = new BasicCookieStore();      // 创建HttpClient上下文      HttpClientContext context = HttpClientContext.create();      context.setCookieStore(cookieStore);        // 创建一个HttpClient      CloseableHttpClient httpClient = HttpClients.custom().setDefaultRequestConfig(globalConfig)          .setDefaultCookieStore(cookieStore).build();        CloseableHttpResponse res = null ;        // 创建本地的HTTP内容      try {        try {          // 创建一个get请求用来获取必要的Cookie，如_xsrf信息          HttpGet get = new HttpGet( "http://www.zhihu.com/" );            res = httpClient.execute(get, context);          // 获取常用Cookie,包括_xsrf信息          System.out.println( "访问知乎首页后的获取的常规Cookie:===============" );          for (Cookie c : cookieStore.getCookies()) {            System.out.println(c.getName() + ": " + c.getValue());          }          res.close();            // 构造post数据          List<NameValuePair> valuePairs = new LinkedList<NameValuePair>();          valuePairs.add( new BasicNameValuePair( "email" , name));          valuePairs.add( new BasicNameValuePair( "password" , password));          valuePairs.add( new BasicNameValuePair( "remember_me" , "true" ));          UrlEncodedFormEntity entity = new UrlEncodedFormEntity(valuePairs, Consts.UTF_8);          entity.setContentType( "application/x-www-form-urlencoded" );            // 创建一个post请求          HttpPost post = new HttpPost( "https://www.zhihu.com/login/email" );          // 注入post数据          post.setEntity(entity);          res = httpClient.execute(post, context);            // 打印响应信息，查看是否登陆是否成功          System.out.println( "打印响应信息===========" );          HttpClientUtils.printResponse(res);          res.close();            System.out.println( "登陆成功后,新的Cookie:===============" );          for (Cookie c : context.getCookieStore().getCookies()) {            System.out.println(c.getName() + ": " + c.getValue());          }            // 构造一个新的get请求，用来测试登录是否成功          HttpGet newGet = new HttpGet( "http://www.zhihu.com/question/following" );          res = httpClient.execute(newGet, context);          String content = EntityUtils.toString(res.getEntity());          System.out.println( "登陆成功后访问的页面===============" );          System.out.println(content);          res.close();          } finally {          httpClient.close();        }      } catch (IOException e) {        e.printStackTrace();      }    } }

转载于:https://www.cnblogs.com/sharpest/p/7832135.html