前言

大多數Java應用程序都會通過HTTP協議來調用接口訪問各種網絡資源，JDK也提供了相應的HTTP工具包，但是使用起來不夠方便靈活，所以我們可以利用Apache的HttpClient來封裝一個具有訪問HTTP協議基本功能的高效工具類，為后續開發使用提供方便。

文章要點：

• HttpClient使用流程
• 工具類封裝
• 使用實例

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HttpClient使用流程

1、導入Maven依賴

<dependency><groupId>org.apache.httpcomponents</groupId><artifactId>httpclient</artifactId><version>4.5.5</version> </dependency> <dependency><groupId>commons-codec</groupId><artifactId>commons-codec</artifactId><version>1.11</version> </dependency> <dependency><groupId>com.google.code.gson</groupId><artifactId>gson</artifactId><version>2.8.5</version> </dependency>

2、創建HttpClient實例

HttpClient client = HttpClientBuilder.create().build();

3、創建請求方法的實例

GET請求使用HttpGet，POST請求使用HttpPost，并傳入請求的URL

// POST請求 HttpPost post = new HttpPost(url); // GET請求，URL中帶請求參數 HttpGet get = new HttpGet(url);

4、添加請求參數

普通形式

List<NameValuePair> list = new ArrayList<>(); list.add(new BasicNameValuePair("username", "admin")); list.add(new BasicNameValuePair("password", "123456"));// GET請求方式 // 由于GET請求的參數是拼裝在URL后方，所以需要構建一個完整的URL，再創建HttpGet實例 URIBuilder uriBuilder = new URIBuilder("http://www.baidu.com"); uriBuilder.setParameters(list); HttpGet get = new HttpGet(uriBuilder.build());// POST請求方式 post.setEntity(new UrlEncodedFormEntity(list, Charsets.UTF_8));

JSON形式

Map<String,String> map = new HashMap<>(); map.put("username", "admin"); map.put("password", "123456"); Gson gson = new Gson(); String json = gson.toJson(map, new TypeToken<Map<String, String>>() {}.getType()); post.setEntity(new StringEntity(json, Charsets.UTF_8)); post.addHeader("Content-Type", "application/json");

5、發送請求

調用HttpClient實例的execute方法發送請求，返回一個HttpResponse對象

HttpResponse response = client.execute(post);

6、獲取結果

String result = EntityUtils.toString(response.getEntity());

7、釋放連接

post.releaseConnection();

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工具類封裝

HttpClient工具類代碼（根據相應使用場景進行封裝）：

public class HttpClientUtil {// 發送GET請求public static String getRequest(String path, List<NameValuePair> parametersBody) throws RestApiException, URISyntaxException {URIBuilder uriBuilder = new URIBuilder(path);uriBuilder.setParameters(parametersBody);HttpGet get = new HttpGet(uriBuilder.build());HttpClient client = HttpClientBuilder.create().build();try {HttpResponse response = client.execute(get);int code = response.getStatusLine().getStatusCode();if (code >= 400)throw new RuntimeException((new StringBuilder()).append("Could not access protected resource. Server returned http code: ").append(code).toString());return EntityUtils.toString(response.getEntity());}catch (ClientProtocolException e) {throw new RestApiException("postRequest -- Client protocol exception!", e);}catch (IOException e) {throw new RestApiException("postRequest -- IO error!", e);}finally {get.releaseConnection();}}// 發送POST請求（普通表單形式）public static String postForm(String path, List<NameValuePair> parametersBody) throws RestApiException {HttpEntity entity = new UrlEncodedFormEntity(parametersBody, Charsets.UTF_8);return postRequest(path, "application/x-www-form-urlencoded", entity);}// 發送POST請求（JSON形式）public static String postJSON(String path, String json) throws RestApiException {StringEntity entity = new StringEntity(json, Charsets.UTF_8);return postRequest(path, "application/json", entity);}// 發送POST請求public static String postRequest(String path, String mediaType, HttpEntity entity) throws RestApiException {logger.debug("[postRequest] resourceUrl: {}", path);HttpPost post = new HttpPost(path);post.addHeader("Content-Type", mediaType);post.addHeader("Accept", "application/json");post.setEntity(entity);try {HttpClient client = HttpClientBuilder.create().build();HttpResponse response = client.execute(post);int code = response.getStatusLine().getStatusCode();if (code >= 400)throw new RestApiException(EntityUtils.toString(response.getEntity()));return EntityUtils.toString(response.getEntity());}catch (ClientProtocolException e) {throw new RestApiException("postRequest -- Client protocol exception!", e);}catch (IOException e) {throw new RestApiException("postRequest -- IO error!", e);}finally {post.releaseConnection();}} }

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使用實例

GET請求

List<NameValuePair> parametersBody = new ArrayList(); parametersBody.add(new BasicNameValuePair("userId", "admin")); String result = HttpClientUtil.getRequest("http://www.test.com/user",parametersBody);

POST請求

List<NameValuePair> parametersBody = new ArrayList(); parametersBody.add(new BasicNameValuePair("username", "admin")); parametersBody.add(new BasicNameValuePair("password", "123456")); String result = HttpClientUtil.postForm("http://www.test.com/login",parametersBody);

POST請求（JSON形式）

Map<String,String> map = new HashMap<>(); map.put("username", "admin"); map.put("password", "123456"); Gson gson = new Gson(); String json = gson.toJson(map, new TypeToken<Map<String, String>>() {}.getType()); String result = HttpClientUtil.postJSON("http://www.test.com/login", json);

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關于HttpClient的詳細介紹看這里：HttpClient入門

本文為作者kMacro原創，轉載請注明來源：https://zkhdev.github.io/2018/10/12/java_dev5/。

轉載于:https://www.cnblogs.com/zkh101/p/9777973.html

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