关于hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found异常

在Spring Cloud中使用断路器后可能会遇到：com.netflix.hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found

典例如下：

@Service
public class OrderService {

    @Autowired
    RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "helloError")
    public String getOrder(Integer a, Integer b){
        return restTemplate.getForObject("http://customer-business-service/show?a="+a+"&b="+b, String.class);
    }

    public String helloError(){
        return "error";
    }
}

访问出现异常：

com.netflix.hystrix.contrib.javanica.exception.FallbackDefinitionException: fallback method wasn't found: helloError([class java.lang.Integer, class java.lang.Integer])
	at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.doFind(MethodProvider.java:190) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.utils.MethodProvider$FallbackMethodFinder.find(MethodProvider.java:159) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.utils.MethodProvider.getFallbackMethod(MethodProvider.java:73) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.utils.MethodProvider.getFallbackMethod(MethodProvider.java:59) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect.setFallbackMethod(HystrixCommandAspect.java:342) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect.access$300(HystrixCommandAspect.java:66) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect$MetaHolderFactory.metaHolderBuilder(HystrixCommandAspect.java:187) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect$CommandMetaHolderFactory.create(HystrixCommandAspect.java:269) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect$MetaHolderFactory.create(HystrixCommandAspect.java:177) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at com.netflix.hystrix.contrib.javanica.aop.aspectj.HystrixCommandAspect.methodsAnnotatedWithHystrixCommand(HystrixCommandAspect.java:95) ~[hystrix-javanica-1.5.12.jar:1.5.12]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_112]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_112]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_112]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_112]

这是因为指定的 备用方法 和 原方法 的参数类型，个数不同造成的。需要统一参数列表，修改成：

    @Autowired
    RestTemplate restTemplate;

    @HystrixCommand(fallbackMethod = "helloError")
    public String getOrder(Integer a, Integer b){
        return restTemplate.getForObject("http://customer-business-service/show?a="+a+"&b="+b, String.class);
    }

    public String helloError(Integer a, Integer b){
        return "error page. params:a="+a+", b="+b;
    }

这样就可以解决上述异常，正常访问了。