<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
  <exclusions>
    <exclusion>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-tomcat</artifactId>
    </exclusion>
  </exclusions>
</dependency>
<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

server:
 undertow:
  max-http-post-size: 0
# 設置IO線程數, 它主要執行非阻塞的任務,它們會負責多個連接, 默認設置每個CPU核心一個線程,數量和CPU 內核數目一樣即可
  io-threads: 4
# 阻塞任務線程池, 當執行類似servlet請求阻塞操作, undertow會從這個線程池中取得線程,它的值設置取決于系統的負載 io-threads*8
  worker-threads: 32
# 以下的配置會影響buffer,這些buffer會用于服務器連接的IO操作,有點類似netty的池化內存管理
# 每塊buffer的空間大小,越小的空間被利用越充分
  buffer-size: 1024
# 每個區分配的buffer數量 , 所以pool的大小是buffer-size * buffers-per-region
#  buffers-per-region: 1024 # 這個參數不需要寫了
# 是否分配的直接內存
  direct-buffers: true

<dependency>
  <groupId>io.github.openfeign</groupId>
  <artifactId>feign-httpclient</artifactId>
</dependency>

# feign配置
feign:
 hystrix:
  # 在feign中開啟hystrix功能，默認情況下feign不開啟hystrix功能
  enabled: true
 ## 配置httpclient線程池
 httpclient:
  enabled: true
 okhttp:
  enabled: false

import java.util.Timer;
import java.util.TimerTask;
import java.util.concurrent.TimeUnit;

import org.apache.http.client.HttpClient;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.impl.client.DefaultConnectionKeepAliveStrategy;
import org.apache.http.impl.client.HttpClientBuilder;
import org.apache.http.impl.conn.PoolingHttpClientConnectionManager;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class HttpPool {

  @Bean
  public HttpClient httpClient(){
    System.out.println("===== Apache httpclient 初始化連接池開始===" );
    // 生成默認請求配置
    RequestConfig.Builder requestConfigBuilder = RequestConfig.custom();
    // 超時時間
    requestConfigBuilder.setSocketTimeout(5 * 1000);
    // 連接時間
    requestConfigBuilder.setConnectTimeout(5 * 1000);
    RequestConfig defaultRequestConfig = requestConfigBuilder.build();
    // 連接池配置
    // 長連接保持30秒
    final PoolingHttpClientConnectionManager pollingConnectionManager = new PoolingHttpClientConnectionManager(30, TimeUnit.MILLISECONDS);
    // 總連接數
    pollingConnectionManager.setMaxTotal(1000);
    // 同路由的并發數
    pollingConnectionManager.setDefaultMaxPerRoute(100);

    // httpclient 配置
    HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
    // 保持長連接配置，需要在頭添加Keep-Alive
    httpClientBuilder.setKeepAliveStrategy(new DefaultConnectionKeepAliveStrategy());
    httpClientBuilder.setConnectionManager(pollingConnectionManager);
    httpClientBuilder.setDefaultRequestConfig(defaultRequestConfig);
    HttpClient client = httpClientBuilder.build();

    // 啟動定時器，定時回收過期的連接
    Timer timer = new Timer();
    timer.schedule(new TimerTask() {
      @Override
      public void run() {
        System.out.println("=====closeIdleConnections===");
        pollingConnectionManager.closeExpiredConnections();
        pollingConnectionManager.closeIdleConnections(5, TimeUnit.SECONDS);
      }
    }, 10 * 1000, 5 * 1000);
    System.out.println("===== Apache httpclient 初始化連接池完畢===");

    return client;
  }
}

<dependency>
  <groupId>org.springframework.cloud</groupId>
  <artifactId>spring-cloud-starter-hystrix</artifactId>
</dependency>

# 配置hystrix的參數
hystrix:
 threadpool:
  # default: 默認參數，作用的所有的hystrix的客戶端,如果需要對某個具體的接口，可以寫接口 方法名稱
  default:
   coreSize: 500
 command:
  default:
   fallback:
    # 是否開啟回退方法
    enabled: true
   execution:
    isolation:
     thread:
      timeoutInMilliseconds: 30000 #缺省為1000