1. 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/
2. 功能介绍
以下列出的是 HttpClient 提供的主要的功能，要知道更多详细的功能可以参见 HttpClient 的主页。
（1）实现了所有 HTTP 的方法（GET,POST,PUT,HEAD 等）
（2）支持自动转向
（3）支持 HTTPS 协议
（4）支持代理服务器等
3. 导入依赖
4.1. 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200if (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();}}
}
4.2. 执行带参数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200if (response.getStatusLine().getStatusCode() == 200) {String content = EntityUtils.toString(response.getEntity(), "UTF-8");System.out.println(content);}} finally {if (response != null) {response.close();}httpclient.close();}}
}
5.1. 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200if (response.getStatusLine().getStatusCode() == 200) {String content = EntityUtils.toString(response.getEntity(), "UTF-8");System.out.println(content);}} finally {if (response != null) {response.close();}httpclient.close();}}
}
5.2. 执行带参数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qList<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200if (response.getStatusLine().getStatusCode() == 200) {String content = EntityUtils.toString(response.getEntity(), "UTF-8");System.out.println(content);}} finally {if (response != null) {response.close();}httpclient.close();}}
}6. 一个封装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uriURIBuilder 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200if (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 blocke.printStackTrace();}}return resultString;}public static String doPost(String url) {return doPost(url, null);}
}
