Hystrix（服务熔断）+Feign和FallbackFactory（服务降级）-526互联

分布式系统面临的服务雪崩问题

当用户发起请求时，假设处理请求的服务器1运行时需要调用到服务器2，服务器2运行时需要调用到服务器3，而如果服务器2因为某些原因始终不能正常调用到服务器3，这时候后面其他用户的请求也都会阻塞在服务器1，在并发量极大的情况下容易导致多个服务器崩溃已经许多其他级联问题的发生，这就是服务雪崩。

测试熔断机制，

为了方便后续复习，直接新建一个有熔断机制的provider8001模块：

步骤：导包->

<?xml version="1.0" encoding="UTF-8"?>
<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">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.example</groupId>
        <artifactId>springcloud</artifactId>
        <version>1.0-SNAPSHOT</version>
    </parent>

    <groupId>com.lian</groupId>
    <artifactId>springcloud-provider-dept-hystrix-8001</artifactId>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-netflix-hystrix -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-hystrix</artifactId>
            <version>2.1.2.RELEASE</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework.cloud/spring-cloud-starter-netflix-eureka-client -->
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-netflix-eureka-client</artifactId>
            <version>2.1.2.RELEASE</version>
        </dependency>
        <!--        #监视器-->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>


        <dependency>
            <groupId>org.example</groupId>
            <artifactId>springcloud-api</artifactId>
            <version>1.0-SNAPSHOT</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>

        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-core</artifactId>
        </dependency>
        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-web -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.1.4.RELEASE</version>
        </dependency>

        <!--        spring-boot-test-->
        <!-- https://mvnrepository.com/artifact/org.springframework.boot/spring-boot-starter-test -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <version>2.1.4.RELEASE</version>
            <scope>test</scope>
        </dependency>



        <!--        jetty-->
        <!--        热部署-->

    </dependencies>

</project>

2.只测试一个get/id的方法，方便对比，在controller类添加备选方法，像我们原来如果没有添加这个备选方法，那么在用户请求不存在的id时，前端就会报错，现在我们有了这个备选方法，当用户请求不存在的id时，前端会打印出提示信息。