Feign Hystrix 熔断

### 熔断示例

*bootstrap.yml* 中开启熔断，设置熔断的超时时间。

```yaml
# Feign
feign:
  hystrix:
    enabled: true

# 熔断
hystrix:
  command:
    default:
      execution:
        isolation:
          thread:
            # 超时时间
            timeoutInMilliseconds: 5000
```

关于超时时间，我的理解是最好设置成大于 **当前 Ribbon 的超时时间 x 重试次数**。关于重试次数，不知道我的理解对不对。

```javascript
ribbon.ReadTimeout * ((ribbon.MaxAutoRetriesNextServer + 1) * (ribbon.MaxAutoRetries + 1))
```

关于熔断的回调处理可以使用 `FeignClient` 注解的 `fallback` 或者 `fallbackFactory` 参数。

使用 `fallbackFactory` 参数的方法可以参考 => [feign自定义fallback方法](https://blog.csdn.net/qq_35807697/article/details/80397933)。

`fallback` 参数用法和 `fallbackFactory` 参数类似，下面是示例代码。

#### 使用 `fallback` 参数

*TestServiceInterface.java*

```java
package com.octopus.middle.api.services.test;

/**
 * Created by liujiajia on 2019/1/21.
 */

import com.octopus.middle.api.model.base.Parameter;
import com.octopus.middle.api.result.base.Result;
import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

/**
 * Test Service
 */
@FeignClient(name = "${service.test}", fallback = TestService.class)
public interface TestServiceInterface {
    /**
     * Not Found
     *
     * @param parameter
     * @return
     */
    @RequestMapping(value = "api/test/not-found", method = RequestMethod.POST)
    Result notFound(Parameter parameter);

/**
     * Time Out
     *
     * @param parameter
     * @return
     */
    @RequestMapping(value = "api/test/time-out", method = RequestMethod.POST)
    Result timeOut(Parameter parameter);
}
```

*TestServer.java*

```java
package com.octopus.middle.api.services.test;

import com.octopus.middle.api.model.base.Parameter;
import com.octopus.middle.api.result.base.Result;
import org.springframework.stereotype.Component;

/**
 * Test Service
 */
@Component
public class TestService implements TestServiceInterface {
    /**
     * 测试
     *
     * @param parameter
     * @return
     */
    @Override
    public Result notFound(Parameter parameter) {
        return new Result() {{
            setIsSuccess(false);
            setMsg("请求测试接口报错！");
        }};
    }

/**
     * Time Out
     *
     * @param parameter
     * @return
     */
    @Override
    public Result timeOut(Parameter parameter) {
        return new Result() {{
            setIsSuccess(false);
            setMsg("请求 Time Out 接口报错！");
        }};
    }
}
```

#### 使用 `fallbackFactory` 参数

*TestServiceInterface.java*

```java
package com.octopus.middle.api.services.test;

/**
 * Created by liujiajia on 2019/1/21.
 */

/**
 * Test Service
 */
@FeignClient(name = "${service.test}", fallbackFactory = TestServiceFallBackFactory.class)
public interface TestServiceInterface {
    /**
     * Not Found
     *
     * @param parameter
     * @return
     */
    @RequestMapping(value = "api/test/not-found", method = RequestMethod.POST)
    Result notFound(Parameter parameter);

/**
     * Time Out
     *
     * @param parameter
     * @return
     */
    @RequestMapping(value = "api/test/time-out", method = RequestMethod.POST)
    Result timeOut(Parameter parameter);
}
```

*TestServiceFallBackFactory.java*

```java
package com.octopus.middle.api.services.test;

import com.octopus.middle.api.model.base.Parameter;
import com.octopus.middle.api.result.base.Result;
import feign.hystrix.FallbackFactory;
import org.springframework.stereotype.Component;

/**
 * Test Service Factory
 * Created by liujiajia on 2019/1/21.
 */
@Component
public class TestServiceFallBackFactory implements FallbackFactory<TestServiceInterface> {
    @Override
    public TestServiceInterface create(Throwable cause) {
        return new TestServiceInterface() {
            /**
             * 测试
             *
             * @param parameter
             * @return
             */
            @Override
            public Result notFound(Parameter parameter) {
                return new Result() {{
                    setIsSuccess(false);
                    setMsg("请求测试接口报错！");
                }};
            }

/**
             * Time Out
             *
             * @param parameter
             * @return
             */
            @Override
            public Result timeOut(Parameter parameter) {
                return new Result() {{
                    setIsSuccess(false);
                    setMsg("请求 Time Out 接口报错！");
                }};
            }
        };
    }
}
```

### 参考

1. [Feign性能优化注意事项](https://www.cnblogs.com/moonandstar08/p/7565442.html)
2. [feign自定义fallback方法](https://blog.csdn.net/qq_35807697/article/details/80397933)
3. [为Spring Cloud Ribbon配置请求重试（Camden.SR2+）](https://www.jianshu.com/p/7af2814db7e9)
4. [Spring cloud 微服务架构之Ribbon/Fegin连接超时ReadTimeout问题](https://blog.csdn.net/m0_38016299/article/details/78391461)

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