依赖：

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpcore</artifactId>
<!--<version>4.4.10</version>-->
</dependency>

<dependency>
<groupId>org.apache.httpcomponents</groupId>
<artifactId>httpclient</artifactId>
<!--<version>4.5.6</version>-->
</dependency>

package org.example.util;

import org.apache.http.HttpEntity;
import org.apache.http.ParseException;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.util.EntityUtils;
import org.springframework.stereotype.Component;

import java.io.IOException;

@Component
public class HttpClientUtil {

public String get(String req){
CloseableHttpClient httpClient = HttpClientBuilder.create().build();
// 创建Get请求
        HttpGet httpGet = new HttpGet("http://localhost:8088/getString");
httpGet.addHeader("req",req);
// 响应模型
        CloseableHttpResponse response = null;
try {
// 由客户端执行(发送)Get请求
            response = httpClient.execute(httpGet);
// 从响应模型中获取响应实体
            HttpEntity responseEntity = response.getEntity();
System.out.println("响应状态为:" + response.getStatusLine());
if (responseEntity != null) {
System.out.println("响应内容长度为:" + responseEntity.getContentLength());
String returnstr = EntityUtils.toString(responseEntity);
System.out.println("响应内容为:" + returnstr);
return returnstr;
            }
        } catch (ClientProtocolException e) {
            e.printStackTrace();
        } catch (ParseException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
try {
// 释放资源
                if (httpClient != null) {
httpClient.close();
                }
if (response != null) {
                    response.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
return null;
    }
}

HttpClient使用简单例子