修改Sentinel错误返回页面

默认Sentinel流控、降级等返回异常都是固定模板。如果需要返回特定内容，需要自定义异常类【MyBlockHandler】，实现【BlockExceptionHandler】接口。
注：1.8以前的版本实现【UrlBlockHandler】

package com.example.demo.config;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import org.springframework.stereotype.Component;

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.csp.sentinel.slots.system.SystemBlockException;
import com.fasterxml.jackson.databind.ObjectMapper;
/**
 * 自定义Sentinel异常实现
 * 
 * @author AdminMall
 *
 */
@Component
public class MyBlockHandler implements BlockExceptionHandler {
     

	@Override
	public void handle(HttpServletRequest request, HttpServletResponse response, BlockException ex) throws Exception {
     
		String msg = null;
		if (ex instanceof FlowException) {
     
			msg = "限流了";
		} else if (ex instanceof DegradeException) {
     
			msg = "降级了";
		} else if (ex instanceof ParamFlowException) {
     
			msg = "热点参数限流";
		} else if (ex instanceof SystemBlockException) {
     
			msg = "系统规则（负载/...不满足要求）";
		} else if (ex instanceof AuthorityException) {
     
			msg = "授权规则不通过";
		}

		// http状态码
		response.setStatus(500);
		response.setCharacterEncoding("utf-8");
		response.setHeader("Content-Type", "application/json;charset=utf-8");
		response.setContentType("application/json;charset=utf-8");
		// msg可以是對象
		new ObjectMapper().writeValue(response.getWriter(), msg);
	}

}