我们在八、springCloudAlibaba-整合sentinel整合了sentinel，这里尝试直接用控制台试用下，并且进行自定义异常。

1、流量控制

从簇点链路中新增流量控制规则

可以看到，配置很简单，我们并没有对我们的业务代码进行影响，配置好后，我们尝试快速点击，发现会返回

Blocked by Sentinel (flow limiting)

那这怎么办呢？我们怎么返回自定义的异常呢？

2、自定义异常

这里有两种方式，一种是用我们之前的每个业务请求都自定义对应的异常，也就是用@SentinelResource注解，比如这次我们加上

    @RequestMapping("/add")
    @SentinelResource(value = "add", blockHandler = "exceptionHandler")
    public String add(String id){
        return "新增订单成功"+id;
    }
    //自定义返回
    public String exceptionHandler(String id, BlockException ex) {
        // Do some log here.
        ex.printStackTrace();
        return "被限流了"+id;
    }

启动后，访问一下请求簇点链路就会有add这个资源名，然后我们再新增流控，发现返回了自定义异常。（注：这里的资源名不能再是/order/add ，不然不会生效的，具体原因后续如果看源码再分析）

上面这种加用注解的方式对我们的代码其实是有侵入的，所以我们可以自定义异常，也很简单，加上下面一个异常类即可,该异常类实现BlockExceptionHandler

package com.suibibk.springCloud.order;
import com.alibaba.csp.sentinel.adapter.spring.webmvc.callback.BlockExceptionHandler;
import com.alibaba.csp.sentinel.slots.block.BlockException;
import com.alibaba.csp.sentinel.slots.block.authority.AuthorityException;
import com.alibaba.csp.sentinel.slots.block.degrade.DegradeException;
import com.alibaba.csp.sentinel.slots.block.flow.FlowException;
import com.alibaba.csp.sentinel.slots.block.flow.param.ParamFlowException;
import com.alibaba.fastjson.JSON;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.MediaType;
import org.springframework.stereotype.Component;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.io.PrintWriter;
@Component
public class MyBlockExceptionHandler implements BlockExceptionHandler {
    Logger log = LoggerFactory.getLogger(this.getClass());
    public void handle(HttpServletRequest httpServletRequest, HttpServletResponse httpServletResponse, BlockException e) throws Exception {
        //getRule返回资源、规则的详细信息
        log.info("BlockExceptionHandler BlockException================"+e.getRule());
        Result r = null;
        if(e instanceof FlowException){
            r = Result.error(100,"接口被限流了");
        }else if (e instanceof DegradeException){
            r = Result.error(101,"服务降级了");
        }else if (e instanceof ParamFlowException){
            r = Result.error(102,"热点参数限流了");
        }else if (e instanceof AuthorityException){
            r = Result.error(104,"授权规则不通过");
        }
        //返回Json数据
        httpServletResponse.setStatus(500);
        httpServletResponse.setCharacterEncoding("UTF-8");
        httpServletResponse.setContentType(MediaType.APPLICATION_JSON_VALUE);
        PrintWriter writer=null;
        try {
            writer=httpServletResponse.getWriter();
            writer.write(JSON.toJSONString(r));
            writer.flush();
        } catch (IOException ioException) {
            log.error("异常：{}",ioException);
        }finally {
            if(writer!=null) {
                writer.close();
            }
        }
    }
}

统一返回封装

package com.suibibk.springCloud.order;
public class Result<T> {
    private Integer code;
    private String msg;
    private T data;
    public Result(Integer code, String msg, T data) {
        this.code = code;
        this.msg = msg;
        this.data = data;
    }
    public Result(Integer code, String msg) {
        this.code = code;
        this.msg = msg;
    }
    public Integer getCode() {
        return code;
    }
    public void setCode(Integer code) {
        this.code = code;
    }
    public String getMsg() {
        return msg;
    }
    public void setMsg(String msg) {
        this.msg = msg;
    }
    public T getData() {
        return data;
    }
    public void setData(T data) {
        this.data = data;
    }
    public static Result error(Integer code,String msg){
        return new Result(code,msg);
    }
}

然后就不用加@SentinelResource注解了，继续控制台新建流控，此时再测试就会返回自定义的反悔了

{
    "code": 100,
    "msg": "接口被限流了"
}

这里推荐用这种方式，对业务逻辑代码侵入较小
后台也打印出了异常的详细信息

2023-11-01 21:20:16.840  INFO 17948 --- [nio-8089-exec-2] c.s.s.order.MyBlockExceptionHandler      : BlockExceptionHandler BlockException================FlowRule{resource=/order/add, limitApp=default, grade=1, count=2.0, strategy=0, refResource=null, controlBehavior=0, warmUpPeriodSec=10, maxQueueingTimeMs=500, clusterMode=false, clusterConfig=ClusterFlowConfig{flowId=null, thresholdType=0, fallbackToLocalWhenFail=true, strategy=0, sampleCount=10, windowIntervalMs=1000, resourceTimeout=2000, resourceTimeoutStrategy=0, acquireRefuseStrategy=0, clientOfflineTime=2000}, controller=com.alibaba.csp.sentinel.slots.block.flow.controller.DefaultController@39a550ee}

我们可以根据这些信息进行更加个性化的异常定制。如果需要更加特殊对某个请求进行专门定制的话，可以用回上面注解的模式！