Hystrix-异常处理

异常的传播和捕获

　　传播：在HystrixCommand实现的run()方法中跑出异常时，除了HystrixBadRequestException之外，其他异常均会被Hystrix认为命令执行失败并处罚服务降级的处理逻辑。下面的例子通过@HystrixCommand注解的ignoreException参数来设置。

　　捕获：我们可以在降级方法中添加Throwable参数来捕获异常。

package org.hope.hystrix.example.exception;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import org.springframework.stereotype.Service;

@Service
public class HystrixHandleException {
    /**
     * 当设置ignoreExceptions参数时，
     * 抛出对应的异常就不会触发降级(也就是不会调用failMethod()方法).
     */
    @HystrixCommand(
            ignoreExceptions = {NullPointerException.class, ArithmeticException.class},
            fallbackMethod = "failMethod"
                    )
    public String getUserName(Long id) {
        Long re = id/0; //会抛ArithmeticException
        String param = null;
        param.trim(); // 此处会抛NullPointException
        return "张三";
    }

    private String failMethod(Long id, Throwable e) {
        return e.getMessage();
    }

}

单元测试：

package org.hope.hystrix.example.exception;

import org.hope.hystrix.example.HystrixApplication;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.context.SpringBootTest;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(classes = HystrixApplication.class)
public class HystrixHandleExceptionTest {

    @Autowired
    private HystrixHandleException hystrixHandleException;
    @Test
    public void test() {
        String name = hystrixHandleException.getUserName(10L);
        System.out.println("==================" + name);
    }

}

运行结果

java.lang.ArithmeticException: / by zero

    at org.hope.hystrix.example.exception.HystrixHandleException.getUserName(HystrixHandleException.java:20)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.netflix.hystrix.contrib.javanica.command.MethodExecutionAction.execute(MethodExecutionAction.java:116)
    at com.netflix.hystrix.contrib.javanica.command.MethodExecutionAction.executeWithArgs(MethodExecutionAction.java:93)
    at com.netflix.hystrix.contrib.javanica.command.MethodExecutionAction.execute(MethodExecutionAction.java:78)
    at com.netflix.hystrix.contrib.javanica.command.GenericCommand$1.execute(GenericCommand.java:48)
    at com.netflix.hystrix.contrib.javanica.command.AbstractHystrixCommand.process(AbstractHystrixCommand.java:145)
    at com.netflix.hystrix.contrib.javanica.command.GenericCommand.run(GenericCommand.java:45)
    at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:302)
    at com.netflix.hystrix.HystrixCommand$2.call(HystrixCommand.java:298)
    at rx.internal.operators.OnSubscribeDefer.call(OnSubscribeDefer.java:46)

参考：

[1]Github，https://github.com/Netflix/Hystrix/wiki/How-it-Works

[2] 《SpringCloud微服务实战》，电子工业出版社，翟永超