前言
大多数Java应用程序都会通过HTTP协议来调用接口访问各种网络资源，JDK也提供了相应的HTTP工具包，但是使用起来不够方便灵活，所以我们可以利用Apache的HttpClient来封装一个具有访问HTTP协议基本功能的高效工具类，为后续开发使用提供方便。
文章要点：
HttpClient使用流程
工具类封装
使用实例
HttpClient使用流程
1、导入Maven依赖
org.apache.httpcomponentshttpclient4.5.5commons-codeccommons-codec1.11com.google.code.gsongson2.8.5
2、创建HttpClient实例
HttpClient client = HttpClientBuilder.create().build();
3、创建请求方法的实例
GET请求使用HttpGet，POST请求使用HttpPost，并传入请求的URL
// POST请求HttpPost post =newHttpPost(url);// GET请求，URL中带请求参数HttpGet get =newHttpGet(url);
4、添加请求参数
普通形式
List list =newArrayList<>();list.add(newBasicNameValuePair("username","admin"));list.add(newBasicNameValuePair("password","123456"));// GET请求方式// 由于GET请求的参数是拼装在URL后方，所以需要构建一个完整的URL，再创建HttpGet实例URIBuilder uriBuilder =newURIBuilder("http://www.baidu.com");uriBuilder.setParameters(list);HttpGet get =newHttpGet(uriBuilder.build());// POST请求方式post.setEntity(newUrlEncodedFormEntity(list, Charsets.UTF_8));
JSON形式
Map map =newHashMap<>();map.put("username","admin");map.put("password","123456");Gson gson =newGson();String json = gson.toJson(map,newTypeToken>() {}.getType());post.setEntity(newStringEntity(json, Charsets.UTF_8));post.addHeader("Content-Type","application/json");
5、发送请求
调用HttpClient实例的execute方法发送请求，返回一个HttpResponse对象
HttpResponse response = client.execute(post);
6、获取结果
String result = EntityUtils.toString(response.getEntity());
7、释放连接
post.releaseConnection();
工具类封装
HttpClient工具类代码（根据相应使用场景进行封装）：
publicclassHttpClientUtil{// 发送GET请求publicstaticStringgetRequest(String path, List<NameValuePair> parametersBody)throwsRestApiException, URISyntaxException{ URIBuilder uriBuilder =newURIBuilder(path); uriBuilder.setParameters(parametersBody); HttpGet get =newHttpGet(uriBuilder.build()); HttpClient client = HttpClientBuilder.create().build();try{ HttpResponse response = client.execute(get);intcode = response.getStatusLine().getStatusCode();if(code >=400)thrownewRuntimeException((newStringBuilder()).append("Could not access protected resource. Server returned http code: ").append(code).toString());returnEntityUtils.toString(response.getEntity()); }catch(ClientProtocolException e) {thrownewRestApiException("postRequest -- Client protocol exception!", e); }catch(IOException e) {thrownewRestApiException("postRequest -- IO error!", e); }finally{ get.releaseConnection(); } }// 发送POST请求（普通表单形式）publicstaticStringpostForm(String path, List<NameValuePair> parametersBody)throwsRestApiException{ HttpEntity entity =newUrlEncodedFormEntity(parametersBody, Charsets.UTF_8);returnpostRequest(path,"application/x-www-form-urlencoded", entity); }// 发送POST请求（JSON形式）publicstaticStringpostJSON(String path, String json)throwsRestApiException{ StringEntity entity =newStringEntity(json, Charsets.UTF_8);returnpostRequest(path,"application/json", entity); }// 发送POST请求publicstaticStringpostRequest(String path, String mediaType, HttpEntity entity)throwsRestApiException{ logger.debug("[postRequest] resourceUrl: {}", path); HttpPost post =newHttpPost(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);intcode = response.getStatusLine().getStatusCode();if(code >=400)thrownewRestApiException(EntityUtils.toString(response.getEntity()));returnEntityUtils.toString(response.getEntity()); }catch(ClientProtocolException e) {thrownewRestApiException("postRequest -- Client protocol exception!", e); }catch(IOException e) {thrownewRestApiException("postRequest -- IO error!", e); }finally{ post.releaseConnection(); } }}
使用实例
GET请求
List parametersBody =newArrayList();parametersBody.add(newBasicNameValuePair("userId","admin"));String result = HttpClientUtil.getRequest("http://www.test.com/user",parametersBody);
POST请求
List parametersBody =newArrayList();parametersBody.add(newBasicNameValuePair("username","admin"));parametersBody.add(newBasicNameValuePair("password","123456"));String result = HttpClientUtil.postForm("http://www.test.com/login",parametersBody);
POST请求（JSON形式）
Map map =newHashMap<>();map.put("username","admin");map.put("password","123456");Gson gson =newGson();String json = gson.toJson(map,newTypeToken>() {}.getType());String result = HttpClientUtil.postJSON("http://www.test.com/login", json); 欢迎工作一到五年的Java工程师朋友们加入Java群： 891219277
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