Spring Cloud学习--hystrix断路器服务容错保护

在Spring Cloud Hystrix中实现了线程隔离、断路器等一系列的服务保护功能，它也是基于Netflix的开源框架 Hystrix实现的，该框架目标在于通过控制那些访问远程系统、服务和第三方库的节点，从而对延迟和故障提供更强大的容错能力。Hystrix具备了服务降级、服务熔断、线程隔离、请求缓存、请求合并以及服务监控等强大功能。

    接下来我们通过简单的demo示例代码来学习一下spring cloud hystrix相关的知识。

1、pom.xml中引入hystrix断路器相关jar

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <parent>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-parent</artifactId>
      <version>1.5.10.RELEASE</version>
  </parent>
  
  <dependencyManagement>
      <dependencies>
          <dependency>
              <groupId>org.springframework.cloud</groupId>
              <artifactId>spring-cloud-dependencies</artifactId>
              <version>Edgware.SR3</version>
              <type>pom</type>
              <scope>import</scope>
          </dependency>
      </dependencies>
  </dependencyManagement>
  <modelVersion>4.0.0</modelVersion>
  <groupId>com.tianjunwei</groupId>
  <artifactId>TJWspringCloud-consumer-hystrix</artifactId>
  <version>1.0.0-SNAPSHOT</version>
  <packaging>jar</packaging>
  <name>TJWspringCloud-consumer</name>
  <dependencies>
      <dependency>
          <groupId>org.springframework.cloud</groupId>
          <artifactId>spring-cloud-starter-hystrix</artifactId>
      </dependency>
      <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-eureka</artifactId>
        </dependency>
        <dependency>  
            <groupId>ch.qos.logback</groupId>  
            <artifactId>logback-core</artifactId>  
        </dependency>  
        <dependency>  
            <groupId>ch.qos.logback</groupId>  
            <artifactId>logback-classic</artifactId>  
        </dependency>  
        <dependency>  
            <groupId>ch.qos.logback</groupId>  
            <artifactId>logback-access</artifactId>  
        </dependency>  
  </dependencies>
  <build>
    <resources>
      <resource>
        <directory>src/main/java</directory>
        <includes>
          <include>**/*.xml</include>
        </includes>
      </resource>
      <resource>
        <directory>src/test/java</directory>
        <includes>
          <include>**/*.xml</include>
        </includes>
      </resource>
      <resource>
        <directory>src/main/resources</directory>
        <includes>
          <include>**/*.*</include>
        </includes>
      </resource>
    </resources>
    <plugins>  
      <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
      </plugin>
      
          <plugin>  
              <groupId>org.apache.maven.plugins</groupId>  
              <artifactId>maven-compiler-plugin</artifactId>  
              <version>2.0.2</version>  
              <configuration>  
                  <source>1.8</source>  
                  <target>1.8</target>  
              </configuration>  
          </plugin>  
      </plugins>  
  </build>
</project>

2、在代码中添加注解@EnableCircuitBreaker表示启用hystrix断路器，通过注解 @HystrixCommand(fallbackMethod = "failback")表示产生异常时调用failback方法

代码示例：

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.cloud.client.circuitbreaker.EnableCircuitBreaker;
import org.springframework.cloud.client.discovery.EnableDiscoveryClient;
import org.springframework.cloud.client.loadbalancer.LoadBalanced;
import org.springframework.cloud.netflix.feign.EnableFeignClients;
import org.springframework.context.annotation.Bean;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.client.RestTemplate;

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

@EnableCircuitBreaker
@EnableFeignClients
@SpringBootApplication
@EnableDiscoveryClient
@RestController
public class ConsumerApplication {
    
    
    @Bean
    @LoadBalanced
    public RestTemplate restTemplate() {
        return new RestTemplate();
    }

    
    @Autowired
    RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "failback")
    @RequestMapping(value = "/add", method = RequestMethod.GET)
    public String add() {
        return restTemplate.getForEntity("http://computer-service/add?a=10&b=20", String.class).getBody();
    }
    
    public String failback() {
        return "client failback";
    }

    @RequestMapping(value = "/info", method = RequestMethod.GET)
    public String info() {
        return "success";
    }
    
    
    public static void main(String[] args) {
        SpringApplication.run(ConsumerApplication.class, args);
    }
}

当调用http://localhost:2011/add接口，服务提供者不在线时会调用failback方法，返回client failback字符串

Spring Cloud Hystrix提供了一个dashboard页面，需要添加相关的jar及相关注解@EnableHystrixDashboard，在pom.xml中添加hystrix dashboard相关的jar

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

重新启动工程访问地址：http://localhost:2011/hystrix