一、什么是httpclient
HTTP 协议可能是现在 Internet 上使用得最多、最重要的协议了，越来越多的 Java 应用程序需要直接通过 HTTP 协议 来访问网络资源；虽然在 JDK 的 java net包中已经提供了访问 HTTP 协议的基本功能，但是对于大部分应用程序来说， JDK 库本身提供的功能还不够丰富和灵活；HttpClient 是 Apache Jakarta Common 下的子项目，用来提供高效的、最新 的、功能丰富的支持 HTTP 协议的客户端编程工具包，并且它支持 HTTP 协议最新的版本和建议 下载地址：http://hc.apache.org/
二、功能介绍
以下列出的是 HttpClient 提供的主要的功能 （1）实现了所有 HTTP 的方法 （2）支持自动转向 （3）支持 HTTPS 协议 （4）支持代理服务器等
要知道更多详细的功能可以参见 HttpClient 的主页
三、导入依赖
<dependency> <groupId>org.apache.httpcomponents</groupId> <artifactId>httpclient</artifactId> <version>${httpclient.version}</version> </dependency>
四、用法示例
（1）执行get请求
public class DoGET { public static void main(String[] args) throws Exception { //创建Httpclient对象 CloseableHttpClient httpclient = HttpClients.createDefault(); //创建http GET请求 HttpGet httpGet = new HttpGet("http://www.baidu.com/"); CloseableHttpResponse response = null; try { //执行请求 response = httpclient.execute(httpGet); //判断返回状态是否为200 if (response.getStatusLine().getStatusCode() == 200) { String content = EntityUtils.toString(response.getEntity(), "UTF-8"); System.out.println("内容长度：" + content.length()); //FileUtils.writeStringToFile(new File("C:\\baidu.html"), content); } } finally { if (response != null) { response.close(); } httpclient.close(); } } }
（2）执行带参数的get请求
public class DoGETParam { public static void main(String[] args) throws Exception { //创建Httpclient对象 CloseableHttpClient httpclient = HttpClients.createDefault(); //定义请求的参数 URI uri = new URIBuilder("http://www.baidu.com/s").setParameter("wd", "java").build();
System.out.println(uri); //创建http GET请求 HttpGet httpGet = new HttpGet(uri);
CloseableHttpResponse response = null; try { //执行请求 response = httpclient.execute(httpGet); //判断返回状态是否为200 if (response.getStatusLine().getStatusCode() == 200) { String content = EntityUtils.toString(response.getEntity(), "UTF-8"); System.out.println(content); } } finally { if (response != null) { response.close(); } httpclient.close(); } } }
（3）执行post请求
public class DoPOST { public static void main(String[] args) throws Exception { //创建Httpclient对象 CloseableHttpClient httpclient = HttpClients.createDefault(); //创建http POST请求 HttpPost httpPost = new HttpPost("http://www.oschina.net/"); CloseableHttpResponse response = null; try { //执行请求 response = httpclient.execute(httpPost); //判断返回状态是否为200 if (response.getStatusLine().getStatusCode() == 200) { String content = EntityUtils.toString(response.getEntity(), "UTF-8"); System.out.println(content); } } finally { if (response != null) { response.close(); } httpclient.close(); } } }
（4）执行带参数的post请求
public class DoPOSTParam { public static void main(String[] args) throws Exception { //创建Httpclient对象 CloseableHttpClient httpclient = HttpClients.createDefault(); //创建http POST请求 HttpPost httpPost = new HttpPost("http://www.oschina.net/search"); //设置2个post参数，一个是scope、一个是q List<NameValuePair> parameters = new ArrayList<NameValuePair>(0); parameters.add(new BasicNameValuePair("scope", "project")); parameters.add(new BasicNameValuePair("q", "java")); //构造一个form表单式的实体 UrlEncodedFormEntity formEntity = new UrlEncodedFormEntity(parameters); //将请求实体设置到httpPost对象中 httpPost.setEntity(formEntity); CloseableHttpResponse response = null; try { //执行请求 response = httpclient.execute(httpPost); //判断返回状态是否为200 if (response.getStatusLine().getStatusCode() == 200) { String content = EntityUtils.toString(response.getEntity(), "UTF-8"); System.out.println(content); } } finally { if (response != null) { response.close(); } httpclient.close(); } } }
（5）封装HttpClient通用工具类
public class HttpClientUtil { public static String doGet(String url, Map<String, String> param) { // 创建Httpclient对象 CloseableHttpClient httpclient = HttpClients.createDefault(); String resultString = ""; CloseableHttpResponse response = null; try { // 创建uri URIBuilder builder = new URIBuilder(url); if (param != null) { for (String key : param.keySet()) { builder.addParameter(key, param.get(key)); } } URI uri = builder.build(); // 创建http GET请求 HttpGet httpGet = new HttpGet(uri); // 执行请求 response = httpclient.execute(httpGet); // 判断返回状态是否为200 if (response.getStatusLine().getStatusCode() == 200) { resultString = EntityUtils.toString(response.getEntity(), "UTF-8"); } } catch (Exception e) { e.printStackTrace(); } finally { try { if (response != null) { response.close(); } httpclient.close(); } catch (IOException e) { e.printStackTrace(); } } return resultString; } public static String doGet(String url) { return doGet(url, null); } public static String doPost(String url, Map<String, String> param) { // 创建Httpclient对象 CloseableHttpClient httpClient = HttpClients.createDefault(); CloseableHttpResponse response = null; String resultString = ""; try { // 创建Http Post请求 HttpPost httpPost = new HttpPost(url); // 创建参数列表 if (param != null) { List<NameValuePair> paramList = new ArrayList<>(); for (String key : param.keySet()) { paramList.add(new BasicNameValuePair(key, param.get(key))); } // 模拟表单 UrlEncodedFormEntity entity = new UrlEncodedFormEntity(paramList); httpPost.setEntity(entity); } // 执行http请求 response = httpClient.execute(httpPost); resultString = EntityUtils.toString(response.getEntity(), "utf-8"); } catch (Exception e) { e.printStackTrace(); } finally { try { response.close(); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } return resultString; } public static String doPost(String url) { return doPost(url, null); } }