1.线程隔离，服务降级（服务的消费方做降级处理）

当服务繁忙时，如果服务出现异常，不是粗暴的直接报错，而是返回一个友好的提示，虽然拒绝了用户的访问，但是会返回一个结果。

这就好比去买鱼，平常超市买鱼会额外赠送杀鱼的服务。等到逢年过节，超时繁忙时，可能就不提供杀鱼服务了，这就是服务的降级。

系统特别繁忙时，一些次要服务暂时中断，优先保证主要服务的畅通，一切资源优先让给主要服务来使用，在双十一、618时，京东天猫都会采用这样的策略。

pom.xml

         
      
       org.springframework.cloud
          
      
       spring-cloud-starter-netflix-hystrix
      
     

UserConsumerApplication.java

package cn.itcast.user; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.cloud.client.SpringCloudApplication; import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker; import org.springframework.cloud.client.discovery.EnableDiscoveryClient; import org.springframework.cloud.client.loadbalancer.LoadBalanced; import org.springframework.context.annotation.Bean; import org.springframework.http.client.OkHttp3ClientHttpRequestFactory; import org.springframework.web.client.RestTemplate; //@EnableDiscoveryClient //@SpringBootApplication //@EnableCircuitBreaker //服务的熔断 @SpringCloudApplication  //SpringCloudApplication可以替代上面三个 public class UserConsumerDemoApplication {
       @Bean     @LoadBalanced  //负载均衡     public RestTemplate restTemplate() {
           // 这次我们使用了OkHttp客户端,只需要注入工厂即可         return new RestTemplate(new OkHttp3ClientHttpRequestFactory());     }     public static void main(String[] args) {
           SpringApplication.run(UserConsumerDemoApplication.class, args);     } }

 3.UserHController.java

package cn.itcast.user.controller;import cn.itcast.user.pojo.User;import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;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.RequestMapping;import org.springframework.web.bind.annotation.RestController;import org.springframework.web.client.RestTemplate;@RestController@RequestMapping("consumerH")public class UserHController {    @Autowired    private RestTemplate restTemplate;    @GetMapping("{id}")    @HystrixCommand(fallbackMethod = "queryUserByIdFallback")   //单个方法的超时返回    public String queryUserById(@PathVariable("id") Long id){        String url = "http://user-service/user/" + id;        //User user = restTemplate.getForObject(url, User.class);        //return  user;        String user = restTemplate.getForObject(url, String.class);        return user;    }    public String queryUserByIdFallback(@PathVariable("id") Long id){        return "用户信息查询出现异常！";//        User user = new User();//        user.setId(id);//        user.setNickName("用户信息查询出现异常！");//        return user;    }} ========================== 配置统一超时信息

package cn.itcast.user.controller; import cn.itcast.user.pojo.User; import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; 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.RequestMapping; import org.springframework.web.bind.annotation.RestController; import org.springframework.web.client.RestTemplate; @RestController @RequestMapping("consumerH") @DefaultProperties(defaultFallback = "queryUserByIdFallback") public class UserHController {
       @Autowired     private RestTemplate restTemplate;     @GetMapping("{id}")     //@HystrixCommand(fallbackMethod = "queryUserByIdFallback")     @HystrixCommand     public String queryUserById(@PathVariable("id") Long id){
           String url = "http://user-service/user/" + id;         //User user = restTemplate.getForObject(url, User.class);         //return  user;         String user = restTemplate.getForObject(url, String.class);         return user;     }     //public String queryUserByIdFallback(@PathVariable("id") Long id){
           //return "用户信息查询出现异常！"; //        User user = new User(); //        user.setId(id); //        user.setNickName("用户信息查询出现异常！"); //        return user;     //}     public String queryUserByIdFallback(){
           return "用户信息查询出现异常！";     } } =============================================================

package cn.itcast.user.controller; import cn.itcast.user.pojo.User; import com.netflix.hystrix.contrib.javanica.annotation.DefaultProperties; import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand; import com.netflix.hystrix.contrib.javanica.annotation.HystrixProperty; 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.RequestMapping; import org.springframework.web.bind.annotation.RestController; import org.springframework.web.client.RestTemplate; @RestController @RequestMapping("consumerH") @DefaultProperties(defaultFallback = "queryUserByIdFallback") public class UserHController {
       @Autowired     private RestTemplate restTemplate;     @GetMapping("{id}")     @HystrixCommand(commandProperties = {
               @HystrixProperty(name = "execution.isolation.thread.timeoutInMilliseconds",value = "3000"),  //响应超时时间             @HystrixProperty(name = "circuitBreaker.requestVolumeThreshold",value = "10"),             @HystrixProperty(name = "circuitBreaker.sleepWindowInMilliseconds",value = "10000"),               @HystrixProperty(name = "circuitBreaker.errorThresholdPercentage",value = "60")     })     public String queryUserById(@PathVariable("id") Long id){
           if(id % 2 ==0){
               throw new RuntimeException("");         }         String url = "http://user-service/user/" + id;         String user = restTemplate.getForObject(url, String.class);         return user;     }     public String queryUserByIdFallback(){
           return "用户信息查询出现异常！";     } }