背景

请求第三方接口或者慢接口需要增加熔断处理，避免因为慢接口qps过大导致应用大量工作线程陷入阻塞以至于其他正常接口都不可用，最近项目测试环境就因为一个查询的慢接口调用次数过多，导致前端整个首页都无法加载。

依赖下载

• springboot

<parent>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-parent</artifactId>
	<version>2.6.3</version>
</parent>
<dependency>
	<groupId>org.springframework.boot</groupId>
	<artifactId>spring-boot-starter-web</artifactId>
</dependency>

• sentinel dashboard
  下载地址：
  https://github.com/alibaba/Sentinel/releases
  版本：
  sentinel-dashboard-1.8.3.jar
  启动命令：
  java -Dserver.port=9000 -Dcsp.sentinel.dashboard.server=localhost:9000 -Dproject.name=sentinel-dashboard -jar sentinel-dashboard-1.8.3.jar
• sentinel springboot 依赖

<dependency>
	<groupId>com.alibaba.cloud</groupId>
	<artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
	<version>2021.0.1.0</version>
</dependency>

熔断尝试

使用SentinelResource注解

• 编写慢接口

@RestController
@RequestMapping(path = "/user")
@RequiredArgsConstructor
@Slf4j
public class UserCtrl {

    private final IUserService userService;

    @GetMapping("/{id}")
    @SneakyThrows
    @SentinelResource(value = "findById", fallback = "findByIdExt")
    public User findById(@PathVariable("id") Long id) {
        TimeUnit.SECONDS.sleep(3);
        return userService.findById(id);
    }

    public User findByIdExt(Long id) {
        log.error("触发熔断");
        throw new IllegalStateException(String.format("id[{}]触发熔断", id));
    }
}

• 应用注册到sentinel dashboard
  添加jvm启动参数：-Dcsp.sentinel.dashboard.server=${sentinel-dashboard域名}:9000
  指定客户端监控 API 的端口（默认是 8719）-Dcsp.sentinel.api.port=8720
  

• 启动应用，进行一次接口调用
  Sentinel 会在客户端首次调用的时候进行初始化，开始向控制台发送心跳包。
  

• 配置熔断规则
  

• 效果
  快速调用3次慢接口，可以看到触发熔断
  10秒熔断失效后可再次成功访问

不使用SentinelResource注解

• 慢接口代码

@RestController
@RequestMapping(path = "/user")
@RequiredArgsConstructor
@Slf4j
public class UserCtrl {

    private final IUserService userService;

    @GetMapping("/{id}")
    @SneakyThrows
    public User findById(@PathVariable("id") Long id) {
        TimeUnit.SECONDS.sleep(3);
        return userService.findById(id);
    }

}

• 配置熔断规则
  
  
• 效果
  快速访问多次慢接口
  
• 对熔断统一添加异常处理

import com.alibaba.csp.sentinel.adapter.spring.webmvc.callback.BlockExceptionHandler;
import com.alibaba.csp.sentinel.slots.block.BlockException;
import com.alibaba.fastjson.JSON;
import com.test.test.model.R;
import lombok.extern.slf4j.Slf4j;
import org.springframework.http.HttpStatus;

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

/**
 * @description sentinel 降级处理
 * @date 2024/6/14
 */
@Slf4j
public class WebBlockExceptionHandler implements BlockExceptionHandler {

    @Override
    public void handle(HttpServletRequest httpServletRequest, HttpServletResponse response, BlockException e) throws Exception {
        log.error(String.format("sentinel 降级 资源名称%s", e.getRule().getResource()), e);

        response.setContentType("application/json");
        response.setStatus(HttpStatus.TOO_MANY_REQUESTS.value());
        response.getWriter().print(JSON.toJSON(R.err(e.getMessage())));
    }
}

import com.alibaba.cloud.sentinel.feign.SentinelFeignAutoConfiguration;
import com.alibaba.csp.sentinel.adapter.spring.webmvc.callback.BlockExceptionHandler;
import com.test.test.hanlder.WebBlockExceptionHandler;
import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

/**
 * @description
 * @date 2024/6/14
 */
@Configuration(proxyBeanMethods = false)
@AutoConfigureBefore(SentinelFeignAutoConfiguration.class)
public class SentinelAutoConfiguration {

    @Bean
    @ConditionalOnMissingBean
    public BlockExceptionHandler blockExceptionHandler() {
        return new WebBlockExceptionHandler();
    }
}

• 统一降级异常处理效果