HttpClient是Apache Jakarta Common下的子项目，可以用来提供高效的、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。

核心API：

发送请求步骤：

• 创建HttpClient对象
• 创建Http请求对象
• 调用HttpClient的execute方法发送请求

通过HttpClient发送get请求

@Test
public void testGET() throws Exception{
    //创建 HttpClient对象
    CloseableHttpClient httpClient = HttpClients.createDefault();

    //创建请求对象
    HttpGet httpGet = new HttpGet("http://localhost:8081/user/shop/status");

    //发送请求，接受响应结果
    CloseableHttpResponse response = httpClient.execute(httpGet);

    //获取服务端返回的状态码
    int statusCode = response.getStatusLine().getStatusCode();
    System.out.println("服务端返回的状态码为："+ statusCode);

    HttpEntity entity = response.getEntity(); // 获取响应体
    String body = EntityUtils.toString(entity);
    System.out.println("服务端返回的为："+ body);

    //关闭资源
    response.close();
    httpClient.close();

}

通过HttpClient发送post请求

@Test
public void testPost() throws Exception{
    //创建httpclient对象
    CloseableHttpClient httpClient = HttpClients.createDefault();

    // 创建请求对象
    HttpPost httpPost = new HttpPost("http://localhost:8081/admin/employee/login");

    JSONObject jsonObject = new JSONObject();
    jsonObject.put("username","admin");
    jsonObject.put("password","123456");

    StringEntity entity = new StringEntity(jsonObject.toString());

    //指定请求编码方式
    entity.setContentEncoding("utf-8");
    //数据格式
    entity.setContentType("application/json");
    httpPost.setEntity(entity);

    //发送请求，接受响应结果
    CloseableHttpResponse response = httpClient.execute(httpPost);

    //解析返回结果
    int statusCode = response.getStatusLine().getStatusCode();
    System.out.println("服务端返回的状态码为："+ statusCode);

    HttpEntity entity1 = response.getEntity();
    String body = EntityUtils.toString(entity1);
    System.out.println("服务端返回的为："+ body);

    //关闭资源
    response.close();
    httpClient.close();
}