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

import org.apache.http.client.HttpClient;
import org.apache.http.impl.client.HttpClientBuilder;
import org.springframework.boot.context.properties.ConfigurationProperties;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.http.client.ClientHttpRequestFactory;
import org.springframework.http.client.HttpComponentsClientHttpRequestFactory;
import org.springframework.http.client.SimpleClientHttpRequestFactory;
import org.springframework.http.converter.HttpMessageConverter;
import org.springframework.http.converter.StringHttpMessageConverter;
import org.springframework.web.client.RestTemplate;

import java.nio.charset.Charset;
import java.util.List;
import java.util.concurrent.TimeUnit;

/**
 * 实际开发中要避免每次http请求都实例化httpclient
 * restTemplate默认会复用连接,保证restTemplate单例即可
 * 参考资料：
 * https://www.cnblogs.com/xrq730/p/10963689.html
 * https://halfrost.com/advance_tcp/
 */

@Configuration
public class RestTemplateConfig {

    @Bean
    RestTemplate restTemplate(ClientHttpRequestFactory clientHttpRequestFactory) {
        RestTemplate restTemplate = new RestTemplate(clientHttpRequestFactory);
        List<HttpMessageConverter<?>> messageConverters = restTemplate.getMessageConverters();
        for (HttpMessageConverter c : messageConverters) {
            if (c instanceof StringHttpMessageConverter) {
                ((StringHttpMessageConverter) c).setDefaultCharset(Charset.forName("utf-8"));
            }
        }

        return restTemplate;
    }

    @Bean
    @ConfigurationProperties(prefix = "spring.resttemplate")
    HttpClientProperties httpClientProperties() {
        return new HttpClientProperties();
    }

    @Bean
    ClientHttpRequestFactory clientHttpRequestFactory(HttpClientProperties httpClientProperties) {
        //如果不使用HttpClient的连接池，则使用restTemplate默认的SimpleClientHttpRequestFactory,底层基于HttpURLConnection
        if (!httpClientProperties.isUseHttpClientPool()) {
            SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();
            factory.setConnectTimeout(httpClientProperties.getConnectTimeout());
            factory.setReadTimeout(httpClientProperties.getReadTimeout());
            return factory;
        }

        //HttpClient4.3及以上版本不手动设置HttpClientConnectionManager,默认就会使用连接池PoolingHttpClientConnectionManager
        HttpClient httpClient = HttpClientBuilder.create().setMaxConnTotal(httpClientProperties.getMaxTotalConnect())
                .setMaxConnPerRoute(httpClientProperties.getMaxConnectPerRoute()).evictExpiredConnections()
                .evictIdleConnections(5000, TimeUnit.MILLISECONDS).build();
        HttpComponentsClientHttpRequestFactory factory = new HttpComponentsClientHttpRequestFactory(httpClient);
        factory.setConnectTimeout(httpClientProperties.getConnectTimeout());
        factory.setReadTimeout(httpClientProperties.getReadTimeout());
        factory.setConnectionRequestTimeout(httpClientProperties.getConnectionRequestTimeout());
        return factory;
    }

}

public class HttpClientProperties {

    /**
     * 是否使用httpclient连接池
     */
    private boolean useHttpClientPool = false;

    /**
     * 从连接池中获得一个connection的超时时间
     */
    private int connectionRequestTimeout = 3000;

    /**
     * 建立连接超时时间
     */
    private int connectTimeout = 3000;

    /**
     * 建立连接后读取返回数据的超时时间
     */
    private int readTimeout = 5000;

    /**
     * 连接池的最大连接数，0代表不限
     */
    private int maxTotalConnect = 128;

    /**
     * 每个路由的最大连接数
     */
    private int maxConnectPerRoute = 32;


    public int getConnectionRequestTimeout() {
        return connectionRequestTimeout;
    }

    public void setConnectionRequestTimeout(int connectionRequestTimeout) {
        this.connectionRequestTimeout = connectionRequestTimeout;
    }

    public int getConnectTimeout() {
        return connectTimeout;
    }

    public void setConnectTimeout(int connectTimeout) {
        this.connectTimeout = connectTimeout;
    }

    public int getReadTimeout() {
        return readTimeout;
    }

    public void setReadTimeout(int readTimeout) {
        this.readTimeout = readTimeout;
    }

    public int getMaxTotalConnect() {
        return maxTotalConnect;
    }

    public void setMaxTotalConnect(int maxTotalConnect) {
        this.maxTotalConnect = maxTotalConnect;
    }

    public int getMaxConnectPerRoute() {
        return maxConnectPerRoute;
    }

    public void setMaxConnectPerRoute(int maxConnectPerRoute) {
        this.maxConnectPerRoute = maxConnectPerRoute;
    }

    public boolean isUseHttpClientPool() {
        return useHttpClientPool;
    }

    public void setUseHttpClientPool(boolean useHttpClientPool) {
        this.useHttpClientPool = useHttpClientPool;
    }
}

spring.resttemplate.connectionRequestTimeout=3000
spring.resttemplate.connectTimeout=3000
spring.resttemplate.readTimeout=10000
spring.resttemplate.maxTotalConnect=256
spring.resttemplate.maxConnectPerRoute=128
spring.resttemplate.useHttpClientPool=true

import com.alibaba.fastjson.JSON;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.HttpMethod;
import org.springframework.http.ResponseEntity;
import org.springframework.test.context.junit4.SpringRunner;
import org.springframework.web.client.RestTemplate;
import org.springframework.web.util.UriComponentsBuilder;
import java.util.Arrays;
import java.util.List;
import java.util.concurrent.ThreadLocalRandom;

@RunWith(SpringRunner.class)
@SpringBootTest
public class RestTemplateTest {

    /**
     * 免费查询号码归属地接口
     */
    public String testUrl = "https://tcc.taobao.com/cc/json/mobile_tel_segment.htm";

    @Autowired
    RestTemplate restTemplate;

    @Test
    public void testRest() {
        HttpHeaders headers = new HttpHeaders();
        headers.set("Accept", "application/json");
        HttpEntity entity = new HttpEntity(headers);

        long start = System.currentTimeMillis();
        for (int i = 0; i < 1000; i++) {
            String tel = getRandomTel();
            UriComponentsBuilder builder = UriComponentsBuilder.fromHttpUrl(testUrl).queryParam("tel", tel);
            System.out.println("发送请求：" + builder.build().encode().toUri());
            long startInner = System.currentTimeMillis();
            ResponseEntity<String> getDistrictRes = restTemplate.exchange(builder.build().encode().toUri(), HttpMethod.GET, entity, String.class);
            long endInner = System.currentTimeMillis();
            System.out.print("costPerRequest:" + (endInner - startInner) + ",i=" + i + "," + Thread.currentThread().getName());
            String resJson = getDistrictRes.getBody().split("=")[1];
            String carrier = (String) JSON.parseObject(resJson).get("carrier");
            System.out.println("," + tel + ",归属地:" + carrier);
        }

        long end = System.currentTimeMillis();
        System.out.println("costTotal:" + (end - start));
    }

    private String getRandomTel() {
        List<String> telList = Arrays.asList("18120168516", "15952044278", "15537788259", "18751872329", "13913329187");
        int index = ThreadLocalRandom.current().nextInt(telList.size());
        return telList.get(index);
    }

}