Java：HttpClient篇，HttpClient4.2在Java中的几则应用：Get、Post参数、Session（会话）保持、Proxy（代理服务器）设置，多线程设置...

新版HttpClient4.2与之前的3.x版本有了很大变化，建议从http://hc.apache.org/处以得到最新的信息。

关于HttpCore与HttpClient：HttpCore是位于HTTP传输组件的底层包，可以用来简化HTTP客户端与服务器端的开发。HttpClient是一个符合HTTP1.1版本，基于HttpCore类包的一个实现。它同时为客户端认证、HTTP状态管理、HTTP连接管理提供了可重用的客户端组件。HttpCore类包目前最新发布版本是httpcore-4.2.4；HttpClient类包的版本是httpclient-4.2.5。
了解到HttpCore包与HttpClient包的差别，在程序中就应该大致知道一些包它们存在于哪个类库中。比如：org.apache.http包属于HttpCore，而org.apache.http.client包属于HttpClient。
HttpClient的API文档在下载的zip中已经包括；
HttpCore的API文档可以参考：http://hc.apache.org/httpcomponents-core-4.2.x/httpcore/apidocs/index.html
HttpClient4.2需要Java 5.0及以上版本；需要支持包有（下载zip包中已经包括）：
* Apache HttpComponents HttpCore
* Apache Commons Logging
* Apache Commons Codec

1. 获取一个HTML页面的内容，一个简单的get应用

    // 获取一个HTML页面的内容，一个简单的get应用

    public void grabPageHTML() throws Exception {

        HttpClient httpclient = new DefaultHttpClient();

        HttpGet httpget = new HttpGet("http://www.baidu.com/");

        HttpResponse response = httpclient.execute(httpget);

        HttpEntity entity = response.getEntity();

        String html = EntityUtils.toString(entity, "GBK");

        

        // releaseConnection等同于reset，作用是重置request状态位，为下次使用做好准备。

        // 其实就是用一个HttpGet获取多个页面的情况下有效果；否则可以忽略此方法。

        httpget.releaseConnection();



        System.out.println(html);

    }

2. 下载一个文件到本地（本示范中为一个验证码图片）

    // 下载一个文件到本地（本示范中为一个验证码图片）

    public void downloadFile() throws Exception {

        String url = "http://www.lashou.com/account/captcha";

        String destfilename = "D:\\TDDOWNLOAD\\yz.png";

        HttpClient httpclient = new DefaultHttpClient();

        HttpGet httpget = new HttpGet(url);

        File file = new File(destfilename);

        if (file.exists()) {

            file.delete();

        }

        

        HttpResponse response = httpclient.execute(httpget);

        HttpEntity entity = response.getEntity();

        InputStream in = entity.getContent();

        try {

            FileOutputStream fout = new FileOutputStream(file);

            int l = -1;

            byte[] tmp = new byte[2048]; 

            while ((l = in.read(tmp)) != -1) {

                fout.write(tmp);

            } 

            fout.close();

        } finally {

            // 在用InputStream处理HttpEntity时，切记要关闭低层流。

            in.close();

        }

        

        httpget.releaseConnection();

    }

3. Post方法，模拟表单提交参数登录到网站并打开会员页面获取内容（会话保持）

    // Post方法，模拟表单提交参数登录到网站。

    // 结合了上面两个方法：grabPageHTML/downloadFile，同时增加了Post的代码。

    public void login2Lashou() throws Exception {

        // 第一步：先下载验证码到本地

        String url = "http://www.lashou.com/account/captcha";

        String destfilename = "D:\\TDDOWNLOAD\\yz.png";

        HttpClient httpclient = new DefaultHttpClient();

        HttpGet httpget = new HttpGet(url);

        File file = new File(destfilename);

        if (file.exists()) {

            file.delete();

        }

        

        HttpResponse response = httpclient.execute(httpget);

        HttpEntity entity = response.getEntity();

        InputStream in = entity.getContent();

        try {

            FileOutputStream fout = new FileOutputStream(file);

            int l = -1;

            byte[] tmp = new byte[2048]; 

            while ((l = in.read(tmp)) != -1) {

                fout.write(tmp);

            } 

            fout.close();

        } finally {

            in.close();

        }

        httpget.releaseConnection();


        

        // 第二步：用Post方法带若干参数尝试登录，需要手工输入下载验证码中显示的字母、数字

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        System.out.println("请输入下载下来的验证码中显示的数字...");

        String yan = br.readLine();



        HttpPost httppost = new HttpPost("http://www.lashou.com/account/login/");

        List<NameValuePair> params = new ArrayList<NameValuePair>();

        params.add(new BasicNameValuePair("user_id", "testuser007"));

        params.add(new BasicNameValuePair("pwd", "asdfg123"));

        params.add(new BasicNameValuePair("yan", yan));

        params.add(new BasicNameValuePair("save_user", "on"));

        params.add(new BasicNameValuePair("save_pwd", "on"));

        params.add(new BasicNameValuePair("sub", "登录"));

        httppost.setEntity(new UrlEncodedFormEntity(params));

        

        response = httpclient.execute(httppost);

        entity = response.getEntity();

        // 在这里可以用Jsoup之类的工具对返回结果进行分析，以判断登录是否成功

        String postResult = EntityUtils.toString(entity, "GBK"); 

        // 我们这里只是简单的打印出当前Cookie值以判断登录是否成功。

        List<Cookie> cookies = ((AbstractHttpClient)httpclient).getCookieStore().getCookies();

        for(Cookie cookie: cookies)

            System.out.println(cookie);

        httppost.releaseConnection();


        

        // 第三步：打开会员页面以判断登录成功（未登录用户是打不开会员页面的）

        String memberpage = "http://www.lashou.com/account/orders/";

        httpget = new HttpGet(memberpage);

        response = httpclient.execute(httpget); // 必须是同一个HttpClient！

        entity = response.getEntity();

        String html = EntityUtils.toString(entity, "GBK");

        httpget.releaseConnection();



        System.out.println(html);

    }

输出：

请输入下载下来的验证码中显示的数字...
sbzq
...

[version: 0][name: login_name2][value: testuser007][domain: www.lashou.com][path: /][expiry: Mon Sep 09 10:21:19 CST 2013]
[version: 0][name: pwd2][value: 4c88a4062736c26572d3ec382868fa2b][domain: lashou.com][path: /][expiry: Mon Sep 09 10:21:19 CST 2013]
?<!doctype html>

...

4. 设置代理服务器

    // 设置代理服务器

    public void testProxy() throws Exception {

        HttpHost proxy = new HttpHost("127.0.0.1", 8888);

        

        // 方式一

        HttpClient httpclient = new DefaultHttpClient();

        httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);

        

        // 方式二

        HttpParams params = new BasicHttpParams(); 

        params.setParameter(ConnRoutePNames.DEFAULT_PROXY, proxy);

        HttpClient httpclient1 = new DefaultHttpClient(params);

    }

5. 几种常用HTTP头的设置

    // 几种常用HTTP头的设置

    public void testBasicHeader() throws Exception {

        HttpParams params = new BasicHttpParams(); 

        Collection<BasicHeader> collection = new ArrayList<BasicHeader>();

        collection.add(new BasicHeader("Accept", "text/html, application/xhtml+xml, */*"));

        collection.add(new BasicHeader("Referer", "http://www.sina.com/"));

        collection.add(new BasicHeader("Accept-Language", "zh-CN"));

        collection.add(new BasicHeader("User-Agent", "Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; WOW64; Trident/6.0)"));

        collection.add(new BasicHeader("Accept-Encoding", "gzip, deflate"));

        params.setParameter(ClientPNames.DEFAULT_HEADERS, collection);

        

        HttpClient httpclient = new DefaultHttpClient(params);

        

        // 下面内容略

    }

6. 多线程编程下的线程池设置

    // 多线程编程下的线程池设置（这点在需要登录且用一个HttpClient对象抓取多个页面的情况下特别有用）

    public void testConnectionManager() throws Exception {

        // 连接池设置

        SchemeRegistry schemeRegistry = new SchemeRegistry();

        schemeRegistry.register(new Scheme("http", 80, PlainSocketFactory.getSocketFactory()));

        schemeRegistry.register(new Scheme("https", 443, SSLSocketFactory.getSocketFactory()));



        PoolingClientConnectionManager cm = new PoolingClientConnectionManager(schemeRegistry);

        cm.setMaxTotal(200); // 连接池里的最大连接数

        cm.setDefaultMaxPerRoute(20); // 每个路由的默认最大连接数

        HttpHost localhost = new HttpHost("locahost", 80); // 可以针对某特定网站指定最大连接数

        cm.setMaxPerRoute(new HttpRoute(localhost), 30);



        // 其它设置

        HttpParams params = new BasicHttpParams(); 

        params.setParameter(ClientPNames.COOKIE_POLICY, CookiePolicy.BROWSER_COMPATIBILITY);

        HttpClient httpclient = new DefaultHttpClient(cm, params);

        

        // 下面内容略

    }

7. 测试HTTP上下文对象（HttpContext）

    // 测试HTTP上下文对象（HttpContext）

    public void testContext() throws Exception {

        // 请求一个页面，然后解析各上下文对象

        DefaultHttpClient httpclient = new DefaultHttpClient();



        HttpContext localContext = new BasicHttpContext();

        HttpGet httpget = new HttpGet("http://www.baidu.com/");



        HttpResponse response = httpclient.execute(httpget, localContext);

        

        // the actual connection to the target server.

        HttpConnection conn = (HttpConnection) localContext.getAttribute(

            ExecutionContext.HTTP_CONNECTION);  

        System.out.println("Socket timeout: " + conn.getSocketTimeout());  



        // the connection target

        HttpHost target = (HttpHost) localContext.getAttribute(

            ExecutionContext.HTTP_TARGET_HOST);

        System.out.println("Final target: " + target);

        

        // the connection proxy, if used 

        HttpHost proxy = (HttpHost) localContext

                .getAttribute(ExecutionContext.HTTP_PROXY_HOST);

        if (proxy != null)

            System.out.println("Proxy host/port: " + proxy.getHostName() + "/"

                    + proxy.getPort());



        // the actual HTTP request

        HttpRequest request = (HttpRequest) localContext

                .getAttribute(ExecutionContext.HTTP_REQUEST);

        System.out.println("HTTP version: " + request.getProtocolVersion());

        Header[] headers = request.getAllHeaders();

        System.out.println("HTTP Headers: ");

        for (Header header : headers) {

            System.out.println("\t" + header.getName() + ": " + header.getValue());

        }

        System.out.println("HTTP URI: " + request.getRequestLine().getUri());



        // the actual HTTP response

        response = (HttpResponse) localContext

                .getAttribute(ExecutionContext.HTTP_RESPONSE);

        HttpEntity entity = response.getEntity();

        if (entity != null) {

            System.out.println("Content Encoding：" + entity.getContentEncoding());

            System.out.println("Content Type：" + entity.getContentType());

        }

        

        // the flag indicating whether the actual request has been fully transmitted to the connection target. 

        System.out.println("Sent flag: " + localContext.getAttribute(ExecutionContext.HTTP_REQ_SENT));


        

        // 如果没有用到返回entity中的内容，那么要把它消费掉，以保证底层的资源得以释放。

        entity = response.getEntity();

        EntityUtils.consume(entity);

    }