1. HttpClient 概述
HttpClient 是 apache 组织下面的一个用于处理 HTTP 请求和响应的开源工具。它不是一个浏览器，也不处理客户端缓存等浏览器的功能。它只是一个类库！它在 JDK 的基本类库基础上做了更好的封装！
HttpClient 项目依赖于 HttpCore（处理核心的 HTTP 协议）、commons-codec（处理与编码有关的问题的项目）和 commons-logging（处理与日志记录有关问题的项目）。
如果你希望能够通过 HttpClient 向服务器上传文件等与 multipart 编码类型有关的请求，以及其它复杂的
MIME 类型，那么，你需要另外一个依赖包：HttpMime（它是专门处理与 MIME 类型有关问题的项目），
开始使用 HttpClient，我们加入了下列依赖包：
httpclient-4.0.1.jar
httpcore-4.0.1.jar
httpmime-4.0.1.jar
- 又依赖于 mime4j（apache-mime4j-0.6.jar）
commons-codec-1.4.jar
commons-logging-1.1.1.jar
commons-io-1.4.jar – 为了更方便处理与 IO 有关的需求
【如果你下载的是包含依赖包的压缩包，那么上述依赖包（除 commons-io-1.4.jar 外）都已经在其中
了！】
2. 了解 JDK 中有关 HTTP URL 处理的 API
因为 HttpClient 是对 JDK 中 java.net.*包下面的有关基础类库的封装，所以，我们有必要了解一下，这
些基础类库的简单用法和概念。
最简单的获取网页内容的示例
@Test public void testURLConnection() { try { String urlString = "http://16.10.113.8:8080/hiapi/paas/asset/db"; URL url = new URL(urlString); //代表了一个网址 URLConnection conn = url.openConnection(); InputStream is = conn.getInputStream(); //获得网页的内容 //将InputStream转换为Reader，并使用缓冲读取，提高效率，同时可以按行 BufferedReader br = new BufferedReader(new InputStreamReader(is, "UTF-8")); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } catch (Exception e) { e.printStackTrace(); } }
运行结果
[{"sign":"paas","deptId":103,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":88,"dbType":"ORACLE","dbName":"nnsptf","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"压测1"},{"sign":"paas","deptId":103,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":96,"dbType":"ORACLE","dbName":"cjecgc","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"测试ora"},{"sign":"paas","deptId":105,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":157,"dbType":"ORACLE","dbName":"uujarl","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"溧水库"},{"sign":"paas","deptId":105,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":164,"dbType":"ORACLE","dbName":"qwxutc","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"溧水数据库2"},{"sign":"paas","deptId":103,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":298,"dbType":"ORACLE","dbName":"vosrtz","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"zijin001"},{"sign":"paas","deptId":103,"hostName":"66.3.125.80,66.3.125.81,66.3.125.82","port":"1521","dbId":299,"dbType":"ORACLE","dbName":"pffklf","isCapture":null,"dbaUser":"system","dbaPwd":"oracle","dbAlias":"zijin002"}] Process finished with exit code 0
3.使用 HttpClient 获取网页内容
3.1 使用 GET 方式向后台递交请求
// org.apache.http.client.HttpClient @Test public void testHttpClient(){ try { //HttpClient主要负责执行请求 HttpClient httpclient = new DefaultHttpClient(); //利用HTTP GET向服务器发起请求 HttpGet get = new HttpGet("http://11.10.113.8:8080/hiapi/paas/asset/db"); //获得服务器响应的的所有信息 HttpResponse response = httpclient.execute(get); //获得服务器响应回来的消息体（不包括HTTP HEAD） HttpEntity entity = response.getEntity(); if(entity != null){ InputStream is = entity.getContent(); //将InputStream转换为Reader，并使用缓冲读取，提高效率，同时 BufferedReader br = new BufferedReader(new InputStreamReader(is,"UTF-8")); String line = null; while((line = br.readLine()) != null){ System.out.println(line); } is.close(); } //释放所有的链接资源，一般在所有的请求处理完成之后，才需要释放 httpclient.getConnectionManager().shutdown(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }
3.2 自动获得响应的编码信息
我们希望程序能够自动分辨响应的内容的编码
@Test public void testHttpClient2() { try { //HttpClient主要负责执行请求 HttpClient httpclient = new DefaultHttpClient(); //利用HTTP GET向服务器发起请求 HttpGet get = new HttpGet("http://66.10.113.8:8080/hiapi/paas/asset/db"); //获得服务器响应的的所有信息 HttpResponse response = httpclient.execute(get); //获得服务器响应回来的消息体（不包括HTTP HEAD） HttpEntity entity = response.getEntity(); if (entity != null) { //获得响应的字符集编码信息 //即获取HTTP HEAD的：ContentType:text/html;charset=UTF-8中的字符集信息 String charset = EntityUtils.getContentCharSet(entity); System.out.println("响应的字符集是：" + charset); InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is, charset)); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } //释放所有的链接资源，一般在所有的请求处理完成之后，才需要释放 httpclient.getConnectionManager().shutdown(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }
3.3 设置代理服务器，访问网站
@Test public void testFetch03() { try { //HttpClient主要负责执行请求 HttpClient httpclient = new DefaultHttpClient(); //设置代理服务器 httpclient.getParams().setParameter(ConnRoutePNames.DEFAULT_PROXY, new HttpHost("121.12.249.207", 3128)); //利用HTTP GET向服务器发起请求 HttpGet get = new HttpGet("http://www.baidu.com/");//new HttpGet("http://localhost:8080/cms"); //获得服务器响应的的所有信息 HttpResponse response = httpclient.execute(get); //获得服务器响应回来的消息体（不包括HTTP HEAD） HttpEntity entity = response.getEntity(); if (entity != null) { //获得响应的字符集编码信息 //即获取HTTP HEAD的：ContentType:text/html;charset=UTF-8中的字符集信息 String charset = EntityUtils.getContentCharSet(entity); System.out.println("响应的字符集是：" + charset); InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is, charset)); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } //释放所有的链接资源，一般在所有的请求处理完成之后，才需要释放 httpclient.getConnectionManager().shutdown(); } catch (ClientProtocolException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } }
3.4 获得重定向之后的网址信息
HttpClient 缺省情况下自动处理客户端重定向，即当你访问网页（比如 A 网页）之后，假设被重定向到了 B 网页，那么，HttpClient 将自动返回 B 网页的内容，无需再编程处理它！有时候我们可能想要知道 A 网 页被重定向到了哪里，也就是取得 B 网页的网址，那么可以通过下述例子获得：
@Test public void testFetch04(){ try { //HttpClient主要负责执行请求 HttpClient httpclient = new DefaultHttpClient(); HttpContext context = new BasicHttpContext(); //利用HTTP GET向服务器发起请求 HttpGet get = new HttpGet("http://localhost:8080/cms/backend/main.jsp"); //获得服务器响应的的所有信息 HttpResponse response = httpclient.execute(get,context); //获得重定向之后的主机地址信息 HttpHost targetHost = (HttpHost)context.getAttribute(ExecutionContext.HTTP_TARGET_HOST); System.out.println(targetHost); // http://localhost:8080 //获得实际的请求对象的URI（即重定向之后的"/cms/backend/login.jsp"） HttpUriRequest actualRequest = (HttpUriRequest) context.getAttribute(ExecutionContext.HTTP_REQUEST); System.out.println(actualRequest.getURI()); //获得服务器响应回来的消息体（不包括HTTP HEAD） HttpEntity entity = response.getEntity(); if(entity != null){ //获得响应的字符集编码信息 //即获取HTTP HEAD的：ContentType:text/html;charset=UTF-8中的字符集信息 String charset = EntityUtils.getContentCharSet(entity); System.out.println("响应的字符集是："+charset); InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is,charset)); String line = null; while((line = br.readLine()) != null){ System.out.println(line); } is.close(); } //释放所有的链接资源，一般在所有的请求处理完成之后，才需要释放 httpclient.getConnectionManager().shutdown(); } catch (Exception e) { e.printStackTrace(); } }
3.5 自动 Cookie 处理
HttpClient 能够支持自动 Cookie 处理。设想一个典型的场景：首先打开登录页面，然后输入用户名和密 码登录，然后访问那些只有登录之后才能访问的网页…… 如果我们用浏览器，因为浏览器可以将登录之后的会话信息用 Cookie 存储在本地，所以，登录之后的每次 请求，都会自动向服务器发送 Cookie 的信息，我们利用 HttpClient，这些过程都全部可以自动化处理 了。
@Test public void testFetch05() { try { //HttpClient主要负责执行请求 HttpClient httpclient = new DefaultHttpClient(); HttpContext context = new BasicHttpContext(); //利用HTTP GET向服务器发起请求， HttpGet get = new HttpGet("http://localhost:8080/cms/backend/login.jsp"); //获得服务器响应的的所有信息 HttpResponse response = httpclient.execute(get, context); //获得服务器响应回来的消息体（不包括HTTP HEAD） HttpEntity entity = response.getEntity(); String charset = null; if (entity != null) { //获得响应的字符集编码信息 //即获取HTTP HEAD的：ContentType:text/html;charset=UTF-8中的字符集信息 charset = EntityUtils.getContentCharSet(entity); System.out.println("响应的字符集是：" + charset); InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is, charset)); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } //************* 执行登录请求 ********************// HttpPost post = new HttpPost("http://localhost:8080/cms/backend/LoginServlet"); //添加POST参数 List<NameValuePair> nvps = new ArrayList<NameValuePair>(); nvps.add(new BasicNameValuePair("username", "admin")); nvps.add(new BasicNameValuePair("password", "admin")); post.setEntity(new UrlEncodedFormEntity(nvps, charset)); response = httpclient.execute(post); entity = response.getEntity(); if (entity != null) { InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is, charset)); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } //******************* 请求文章查询 ********************// get = new HttpGet("http://localhost:8080/cms/backend/ArticleServlet"); response = httpclient.execute(get); entity = response.getEntity(); if (entity != null) { InputStream is = entity.getContent(); //使用响应中的编码来解释响应的内容 BufferedReader br = new BufferedReader(new InputStreamReader(is, charset)); String line = null; while ((line = br.readLine()) != null) { System.out.println(line); } is.close(); } //释放所有的链接资源，一般在所有的请求处理完成之后，才需要释放 httpclient.getConnectionManager().shutdown(); } catch (Exception e) { e.printStackTrace(); } }
