在Spring Cloud Feign工程中配置斷路器Hystrix的時候，pom.xml檔案已經加入Hystrix相關的jar：

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-actuator</artifactId>
        </dependency>

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

Application.java:

@SpringBootApplication
@EnableDiscoveryClient
@EnableFeignClients
@EnableHystrix
@EnableHystrixDashboard
public class Application
 
 {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

當啟動的時候，報如下錯誤：

Exception in thread "main" java.lang.NoClassDefFoundError: com/netflix/hystrix/contrib/javanica/aop/aspectj/HystrixCommandAspect
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang
 
.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.getDeclaredMethods(Class.java:1975)
    at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:613)
    at org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:524)
    at org.springframework.util.ReflectionUtils.doWithMethods(ReflectionUtils.java:510)
    at org.springframework.util.ReflectionUtils.getUniqueDeclaredMethods(ReflectionUtils.java:570)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getTypeForFactoryMethod(AbstractAutowireCapableBeanFactory.java:697)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.determineTargetType(AbstractAutowireCapableBeanFactory.java:640)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.predictBeanType(AbstractAutowireCapableBeanFactory.java:609)
    at org.springframework.beans.factory.support.AbstractBeanFactory.isFactoryBean(AbstractBeanFactory.java:1484)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doGetBeanNamesForType(DefaultListableBeanFactory.java:425)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeanNamesForType(DefaultListableBeanFactory.java:395)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeansOfType(DefaultListableBeanFactory.java:515)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBeansOfType(DefaultListableBeanFactory.java:508)
    at org.springframework.context.support.AbstractApplicationContext.getBeansOfType(AbstractApplicationContext.java:1186)
    at org.springframework.boot.SpringApplication.getExitCodeFromMappedException(SpringApplication.java:818)
    at org.springframework.boot.SpringApplication.getExitCodeFromException(SpringApplication.java:804)
    at org.springframework.boot.SpringApplication.handleExitCode(SpringApplication.java:790)
    at org.springframework.boot.SpringApplication.handleRunFailure(SpringApplication.java:744)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:314)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1118)
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1107)

在pom.xml檔案中加入：

    <!-- https://mvnrepository.com/artifact/com.netflix.hystrix/hystrix-javanica -->
        <dependency>
            <groupId>com.netflix.hystrix</groupId>
            <artifactId>hystrix-javanica</artifactId>
            <version>1.5.12</version>
        </dependency>

問題解決OK！

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