**Hystrix 容错机制**
在不改变各个服务器调用关系的前提下，针对错误情况进行预先处理。
设计原则：
1）服务隔离机制
2）服务降级机制
3）熔断机制
4）提供实时的监控和报警功能
5）提供实时的配置修改功能
Hystrix数据监控需要结合Spring Cloud Actuator来使用，Actuator提供了
对服务的健康监控、数据统计，可以通过hystrix.stream节点获取监控的请求数据，
提供了可视化的监控界面。
创建maven模块
pom.xml
```yaml
<dependencies>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
<version>2.0.2.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-openfeign</artifactId>
<version>2.0.2.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-actuator</artifactId>
<version>2.0.7.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
<version>2.0.2.RELEASE</version>
</dependency>
<dependency>
<groupId>org.springframework.cloud</groupId>
<artifactId>spring-cloud-starter-netflix-hystrix-dashboard</artifactId>
<version>2.0.2.RELEASE</version>
</dependency>
</dependencies>
```
创建配置文件 application.yml
```yaml
server:
port: 8060
spring:
application:
name: hystrix
eureka:
client:
service-url:
defaultZone: http://localhost:8761/eureka/
instance:
prefer-ip-address: true
feign:
hystrix:
enabled: true
management:
endpoints:
web:
exposure:
include: 'hystrix.stream'
```
创建启动类
```java
package com.shuang;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.netflix.hystrix.dashboard.EnableHystrixDashboard;
import org.springframework.cloud.openfeign.EnableFeignClients;
@SpringBootApplication
@EnableFeignClients
@EnableCircuitBreaker
@EnableHystrixDashboard
public class HystrixApplication {
public static void main(String[] args) {
SpringApplication.run(HystrixApplication.class,args);
}
}
```
注解说明：
@EnableCircuitBreaker：声明启用数据监控
@EnableHystrixDashboard：声明启用可视化数据监控
Handler
```java
package com.shuang.controller;
import com.shuang.entity.Student;
import com.shuang.feign.FeignProviderClient;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import java.util.Collection;
@RestController
@RequestMapping("/hystrix")
public class HystrixHandler {
@Autowired
private FeignProviderClient feignProviderClient;
@GetMapping("/findAll")
public Collection<Student> findAll(){
return feignProviderClient.findAll();
}
@GetMapping("/index")
public String index(){
return feignProviderClient.index();
}
}
```
启动成功后，访问http://localhost:8060/actuator/hystrix.stream 可以监控到请求数据
访问 http://localhost:8060/hystrix，可以看到可视化的监控界面，输入要监控的地址节点，
即可看到该节点的可视化数据监控。
feign提供了服务熔断，与笔记7相同，这里就不啰嗦了
