HttpClient工具类
https://www.cnblogs.com/chenmz1995/p/11050927.html
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
<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、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 = new HttpPost(url);
// GET请求，URL中带请求参数
HttpGet get = new HttpGet(url);
4、添加请求参数
普通形式
List<NameValuePair> list = new ArrayList<>();
list.add(new BasicNameValuePair("username", "admin"));
list.add(new BasicNameValuePair("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 = new URIBuilder("http://www.baidu.com");
uriBuilder.setParameters(list);
HttpGet get = new HttpGet(uriBuilder.build());
// POST请求方式
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、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）：
public class HttpClientUtil {
// 发送GET请求
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();
}
}
// 发送POST请求（普通表单形式）
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);
}
// 发送POST请求（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);
}
// 发送POST请求
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();
}
}
}
使用实例
GET请求
List<NameValuePair> parametersBody = new ArrayList();
parametersBody.add(new BasicNameValuePair("userId", "admin"));
String result = HttpClientUtil.getRequest("http://www.test.com/user",parametersBody);
POST请求
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请求（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);
关于HttpClient的详细介绍看这里：HttpClient入门
本文为作者kMacro原创，转载请注明来源：https://zkhdev.github.io/2018/10/12/java_dev5/。