简介

服务降级是一种增强用户体验的方式。当用户的请求由于各种原因被拒后，系统返回-一个事先设定好的、用户可以接受的，但又令用户并不满意的结果。这种请求处理方式称为服务降级。

Sentinel方法级降级

1. 导入依赖

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

2. contreller层写法

    /**
     * 根据id查询部门
     */
    @SentinelResource(fallback = "getFallBack")
    @GetMapping("/get/{id}")
    public Depart get(@PathVariable Long id) {
        return restTemplate.getForObject(PROVIDER_URL + "/get/" + id, Depart.class);
    }

    /**
     * 服务降级使用的方法
     */
    public Depart getFallBack(Long id, Throwable t) {
        log.info("id = " + id);
        log.info("throwable = " + t.getMessage());
        Depart depart = new Depart();
        depart.setId(id);
        depart.setName("no this depart");
        return  depart;
    }

在调用get(@PathVariable Long id) 出错的情况下会调用降级的getFallBack(Long id) 方法。

3.验证

get(@PathVariable Long id)不能被访问。

日志

2023-12-01T19:50:26.401+08:00  INFO 17500 --- [nio-8080-exec-2] com.zjw.controller.DepartController      : id = 1
2023-12-01T19:50:26.401+08:00  INFO 17500 --- [nio-8080-exec-2] com.zjw.controller.DepartController      : throwable = No instances available for depart-provider

Sentinel类级降级

1. 定义降级使用的类

方法需要是static声明

package com.zjw.controller.fallback;

import com.zjw.domain.Depart;
import lombok.extern.slf4j.Slf4j;

import java.util.List;

/**
 * DepartControllerFallBack
 * @since 2023/12/01 19:56
 */
@Slf4j
public class DepartControllerFallBack {
    /**
     * 服务降级使用的方法
     */
    public static Depart getFallBack(Long id, Throwable t) {
        log.info("id = " + id);
        log.info("throwable = " + t.getMessage());
        Depart depart = new Depart();
        depart.setId(id);
        depart.setName("no this depart");
        return  depart;
    }

    /**
     * 服务降级使用的方法
     */
    public static List<Depart> listFallBack(Throwable t) {
        log.info("listFallBack");
        log.info("throwable = " + t.getMessage());
        Depart depart = new Depart();
        depart.setName("no this depart");
        return List.of(depart);
    }
}

2. Controller层

在需要降级的方法上标注上降级使用的方法和类

package com.zjw.controller;

import com.alibaba.csp.sentinel.annotation.SentinelResource;
import com.zjw.controller.fallback.DepartControllerFallBack;
import com.zjw.domain.Depart;
import jakarta.annotation.Resource;
import lombok.extern.slf4j.Slf4j;
import org.springframework.web.bind.annotation.*;
import org.springframework.web.client.RestTemplate;

import java.util.List;

/**
 * <p>
 * 部门表 前端控制器
 * </p>
 *
 * @since 2023-11-20
 */
@RestController
@RequestMapping("/depart")
@Slf4j
public class DepartController {

    @Resource
    private RestTemplate restTemplate;

    private static final String PROVIDER_URL = "http://depart-provider/depart";


    /**
     * 根据id查询部门
     */
    @SentinelResource(fallback = "getFallBack" , fallbackClass = DepartControllerFallBack.class)
    @GetMapping("/get/{id}")
    public Depart get(@PathVariable Long id) {
        return restTemplate.getForObject(PROVIDER_URL + "/get/" + id, Depart.class);
    }

    /**
     * 查询所有部门
     */
    @SuppressWarnings("unchecked")
    @SentinelResource(fallback = "listFallBack" , fallbackClass = DepartControllerFallBack.class)
    @GetMapping("/list")
    public List<Depart> list() {
        return (List<Depart>)restTemplate.getForObject(PROVIDER_URL + "/list", List.class);
    }
}

3. 验证

OpenFeign类级降级

导入依赖

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>3.0.2</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.zjw</groupId>
    <artifactId>sc-06-consumer-sentinel-degrade-openfeign-8080</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>sc-06-consumer-sentinel-degrade-openfeign-8080</name>
    <description>sc-06-consumer-sentinel-degrade-openfeign-8080</description>
    <properties>
        <java.version>17</java.version>
        <spring-cloud.version>2022.0.0</spring-cloud.version>
        <spring-cloud-alibaba.version>2022.0.0.0</spring-cloud-alibaba.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-sentinel</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <exclusions>
                <exclusion>
                    <groupId>org.yaml</groupId>
                    <artifactId>snakeyaml</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-loadbalancer</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-starter-openfeign</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba.cloud</groupId>
            <artifactId>spring-cloud-starter-alibaba-nacos-discovery</artifactId>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.yaml</groupId>
            <artifactId>snakeyaml</artifactId>
            <version>2.2</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>
    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework.cloud</groupId>
                <artifactId>spring-cloud-dependencies</artifactId>
                <version>${spring-cloud.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
            <dependency>
                <groupId>com.alibaba.cloud</groupId>
                <artifactId>spring-cloud-alibaba-dependencies</artifactId>
                <version>${spring-cloud-alibaba.version}</version>
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
                <configuration>
                    <image>
                        <builder>paketobuildpacks/builder-jammy-base:latest</builder>
                    </image>
                    <excludes>
                        <exclude>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                        </exclude>
                    </excludes>
                </configuration>
            </plugin>
        </plugins>
    </build>

</project>

开打sentinel对openfeign支持

server:
  port: 8080

spring:
  application:
    name: depart-consumer # 微服务名称
  cloud:
    nacos:
      discovery:
        server-addr: nacos-local:8848 # nacos注册中心地址
        username: nacos # 用户名密码
        password: nacos
    openfeign:
      client:
        config:
          default:  # 这是一个map，设置默认配置
            connect-timeout: 5000 # 连接超时时间
            read-timeout: 5000  # 响应超时时间
          depart-provider:  # 指定服务的设置
            connect-timeout: 4000 # 连接超时时间
            read-timeout: 4000  # 响应超时时间

feign:  # 打开 sentinel 对 feign 的支持
  sentinel:
    enabled: true

编写sentinel类

注意@RequestMapping("/fallback/depart")

package com.zjw.service;

import com.zjw.domain.Depart;
import lombok.extern.slf4j.Slf4j;
import org.springframework.stereotype.Component;
import org.springframework.web.bind.annotation.RequestMapping;

import java.util.List;

/**
 * @since 2023/12/01 21:11
 */
@Component
@Slf4j
@RequestMapping("/fallback/depart")
public class DepartServiceFallBack implements IDepartService{

    @Override
    public boolean save(Depart depart) {
        log.info("save..fallback");
        return false;
    }

    @Override
    public boolean remove(Long id) {
        log.info("remove..fallback");
        return false;
    }

    @Override
    public boolean update(Depart depart) {
        log.info("update..fallback");
        return false;
    }

    @Override
    public Depart get(Long id) {
        log.info("get..fallback");
        return null;
    }

    @Override
    public List<Depart> list() {
        log.info("list..fallback");
        return null;
    }

    @Override
    public List<String> discovery() {
        log.info("discovery..fallback");
        return null;
    }
}

在接口上标注使用的fallback类

@FeignClient(value = "depart-provider", path = "/depart", fallback = DepartServiceFallBack.class)
public interface IDepartService {
  ....
}

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