Hystrix 熔断：

　　首先仍然启动Eureka,这里就不说了。

OrderController.java:

package com.tuling.cloud.study.user.controller;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.tuling.cloud.study.user.entity.User;

@RestController
public class OrderController {
  private static final Logger logger = LoggerFactory.getLogger(OrderController.class);
  @Autowired
  private RestTemplate restTemplate;
  

  @HystrixCommand(fallbackMethod = "findByIdFallback")
  @GetMapping("/user/{id}")
  public User findById(@PathVariable Long id) {
    logger.error("================请求用户中心接口，用户id:" + id + "==============");
    return restTemplate.getForObject("http://microservice-provider-user/" + id, User.class);
  }

  //降级方法
  public User findByIdFallback(Long id) { 
    User user = new User();
    user.setId(-1L);
    user.setName("默认用户");
    return user;
  }

}

order 服务和上一章一样唯一修改的是yml文件：

server:
  port: 9010
spring:
  application:
    name: microservice-consumer-order
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true
hystrix:
  command:
    default:
      circuitBreaker:
        requestVolumeThreshold: 3 #默认20，熔断的阈值，如何user服务报错满足3次，熔断器就会打开，就算order之后请求正确的数据也不行。
        sleepWindowInMilliseconds: 5000 #默认5S ， 等5S之后熔断器会处于半开状态，然后下一次请求的正确和错误讲决定熔断器是否真的关闭和是否继续打开

user服务修改UserController.java其余不变

package com.tuling.cloud.study.controller;

import java.util.Random;

import org.apache.log4j.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.serviceregistry.Registration;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import com.tuling.cloud.study.entity.User;
import com.tuling.cloud.study.repository.UserRepository;

@RestController
public class UserController {
    
  private final Logger logger = Logger.getLogger(getClass());
    
  @Autowired
  private UserRepository userRepository;
  @Autowired
  private Registration registration;
  

  @GetMapping("/{id}")
  public User findById(@PathVariable Long id) throws Exception {
      logger.info("用户中心接口：查询用户"+ id +"信息");
      //测试熔断，传入不存在的用户id模拟异常情况
      if (id == 10) {
        throw new NullPointerException();
      }
      User findOne = userRepository.findOne(id);
      return findOne;
  }
  
  @GetMapping("/getIpAndPort")
  public String findById() {
      return registration.getHost() + ":" + registration.getPort();
  }
}

user服务模拟接口报错，order服务在调用的时候如果id传入的是10 ，就会导致user服务报错，那么满足3次报错之后，熔断器就会打开。注意：之后在5S内浏览器继续请求order服务的findById()接口是不会进入的，hystrix会直接执行降级方法。

等5S过去之后，hytrix不会全打开，而是处于半开状态，接下来的第一个请求决定熔断器是否继续打开，还是关闭。

演示：

springcloud(六) Hystrix 熔断，限流

特别注意“：user服务报错满足3次，就导致调用方order的 findById() 进不去了，而是直接进入降级方法。这就是熔断。

Hystrix 限流：

Eureka 还是用同样的（略）

order工程截图：

springcloud(六) Hystrix 熔断，限流

pom.xml 和上一章一样（略）

OrderController.java:

package com.jiagoushi.cloud.study.user.controller;

import com.jiagoushi.cloud.study.user.entity.User;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty;

@RestController
public class OrderController {

    private static final Logger logger = LoggerFactory.getLogger(OrderController.class);

    @Autowired
    private RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "findByIdFallback", 
                    groupKey = "orderUserGroup", 
                    threadPoolKey = "orderUserIdThreadPool", 
                    threadPoolProperties = {
                        @HystrixProperty(name = "coreSize", value = "2"), 
                        @HystrixProperty(name = "maxQueueSize", value = "2"),
                        @HystrixProperty(name = "queueSizeRejectionThreshold", value = "1") }) //maxQueueSize和queueSizeRejectionThreshold 简单理解两者取最小值做为队列长度
    @GetMapping("/user/{id}")
    public User findById(@PathVariable Long id) {
        logger.info("================请求用户中心接口，用户id:" + id + "==============");
        return restTemplate.getForObject("http://microservice-provider-user/" + id, User.class);
    }

    @HystrixCommand(fallbackMethod = "findByIdFallback",
            groupKey = "orderUserGroup",
            threadPoolKey = "orderUserIdThreadPool",
            threadPoolProperties = {
                    @HystrixProperty(name = "coreSize", value = "2"), //配置线程池线程数量
                    @HystrixProperty(name = "maxQueueSize", value = "2"),
                    @HystrixProperty(name = "queueSizeRejectionThreshold", value = "1") })
    @GetMapping("/user/{userName}")
    public User findByUserName(@PathVariable String userName) {
        logger.info("================请求用户中心接口，用户userName:" + userName + "==============");
        return restTemplate.getForObject("http://microservice-provider-user/" + userName, User.class);
    }

    //降级方法
    public User findByIdFallback(Long id) {
        User user = new User();
        user.setId(-1L);
        user.setName("默认用户");
        return user;
    }
    
}

说明：

hystix 默认线程池大小是10。
groupKey 是服务分组， threadPoolKey 是线程池标识，也就是说当groupKey和threadPoolKey 同时修饰findById() 和findByUserName() 时，他们共用一个线程池，大小共10。
ThreadPoolProperties：配置线程池参数，coreSize配置核心线程池大小和线程池最大大小，keepAliveTimeMinutes是线程池中空闲线程生存时间（如果不进行动态配置，那么是没有任何作用的），maxQueueSize配置线程池队列最大大小， queueSizeRejectionThreshold限定当前队列大小，即实际队列大小由这个参数决定，通过改变queueSizeRejectionThreshold可以实现动态队列大小调整。

applciation.xml:

server:
  port: 9010
spring:
  application:
    name: microservice-consumer-order
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true
hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            timeoutInMilliseconds: 20000 #命令执行超时时间，默认1000ms,就是调接口的响应时间超过20S就执行降级，不管提供者是否挂机还是延迟超过时间就走降级

user工程截图：

springcloud(六) Hystrix 熔断，限流

pom.xml 和上一章一样（略）

UserController.java:

package com.jiagoushi.cloud.study.controller;

import com.jiagoushi.cloud.study.entity.User;
import org.apache.log4j.Logger;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.cloud.client.serviceregistry.Registration;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RestController;

import com.jiagoushi.cloud.study.repository.UserRepository;

@RestController
public class UserController {
    
  private final Logger logger = Logger.getLogger(getClass());
    
  @Autowired
  private UserRepository userRepository;
  @Autowired
  private Registration registration;
  

  @GetMapping("/{id}")
  public User findById(@PathVariable Long id) throws Exception {
      logger.info("用户中心接口：查询用户"+ id +"信息");
      // 配合限流演示，模拟业务耗时3S
      　　 Thread.sleep(3000);
      User findOne = userRepository.findOne(id);
      return findOne;
  }
  
  @GetMapping("/getIpAndPort")
  public String findById() {
      return registration.getHost() + ":" + registration.getPort();
  }
}

　　application.yml：

server:
  port: 8002
spring:
  application:
    name: microservice-provider-user
  jpa:
    generate-ddl: false
    show-sql: true
    hibernate:
      ddl-auto: none
  datasource:                           # 指定数据源
    platform: h2                        # 指定数据源类型
    schema: classpath:schema.sql        # 指定h2数据库的建表脚本
    data: classpath:data.sql            # 指定h2数据库的数据脚本
logging:                                # 配置日志级别，让hibernate打印出执行的SQL
  level:
    root: INFO
    org.hibernate: INFO
    org.hibernate.type.descriptor.sql.BasicBinder: TRACE
    org.hibernate.type.descriptor.sql.BasicExtractor: TRACE
eureka:
  client:
    serviceUrl:
      defaultZone: http://localhost:8761/eureka/
  instance:
    prefer-ip-address: true