背景

思考下这段代码，想想项目中是不是到处存在
先查缓存，缓存里面有，直接返回；缓存没有，查数据库，并更新到缓存
思考：如何将缓存代码从业务代码中剥离，促使业务代码更简洁更易维护，可以把这部分通过AOP来统一处理

前置知识

提前预习一波 SpringEL 表达式

改造代码

首先配置

spring.datasource.url=jdbc:mysql://192.168.133.128:3306/wxpay?useUnicode=true&characterEncoding=utf-8&rewriteBatchedStatements=true&useSSL=false&serverTimezone=Asia/Shanghai
spring.datasource.username=root
spring.datasource.password=root
spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver#mybatis-plus.configuration.log-impl=org.apache.ibatis.logging.stdout.StdOutImpl
mybatis-plus.mapper-locations=classpath*:mapper/*.xmlspring.data.redis.database=0
spring.data.redis.host=192.168.133.128
spring.data.redis.port=6379
spring.data.redis.password=123456
spring.data.redis.lettuce.pool.max-active=8
spring.data.redis.lettuce.pool.max-wait=-1ms
spring.data.redis.lettuce.pool.max-idle=8
spring.data.redis.lettuce.pool.min-idle=0

注解和切面定义

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)
@Documented
public @interface MyRedisCacheAnnotation {String keyPrefix();String matchValue();
}

@Slf4j
@Aspect
@Component
public class MyRedisCacheAspect {@Resourceprivate RedisTemplate redisTemplate;@Pointcut("@annotation(com.example.demo.annotation.MyRedisCacheAnnotation)")public void cachePointCut() {}@Around("cachePointCut()")public Object doCache(ProceedingJoinPoint pjp) {Object result = null;try {// 获得重载后的方法名MethodSignature signature = (MethodSignature) pjp.getSignature();Method method = signature.getMethod();// 确定方法名后获得该方法上面的注解标签 MyRedisCacheAnnotationMyRedisCacheAnnotation annotation = method.getAnnotation(MyRedisCacheAnnotation.class);// 获取注解上配置的参数String keyPrefix = annotation.keyPrefix();String matchValue = annotation.matchValue();// SpringEL 解析器SpelExpressionParser spelExpressionParser = new SpelExpressionParser();Expression expression = spelExpressionParser.parseExpression(matchValue); // #idStandardEvaluationContext context = new StandardEvaluationContext();// 获得方法的形参个数Object[] args = pjp.getArgs();DefaultParameterNameDiscoverer defaultParameterNameDiscoverer = new DefaultParameterNameDiscoverer();String[] parameterNames = defaultParameterNameDiscoverer.getParameterNames(method);for (int i = 0; i < parameterNames.length; i++) {log.info("方法参数名称：{}, 值:{}", parameterNames[i], args[i].toString());context.setVariable(parameterNames[i], args[i].toString());}// 拼接 redis 的最终 key 形式String key = keyPrefix + ":" + expression.getValue(context).toString();log.info("key形式{}", key);// 先去 redis 看看有没有result = redisTemplate.opsForValue().get(key);if (result != null) {log.info("redis里有，直接返回了");return result;}result = pjp.proceed();if (result != null) {redisTemplate.opsForValue().set(key, result);}} catch (Throwable e) {e.printStackTrace();}return result;}
}

不要忘了重写 redisTemplate

@Configuration
public class RedisConfig {@Beanpublic RedisTemplate<String, Object> redisTemplate(LettuceConnectionFactory lettuceConnectionFactory) {RedisTemplate<String, Object> redisTemplate = new RedisTemplate<>();redisTemplate.setConnectionFactory(lettuceConnectionFactory);redisTemplate.setKeySerializer(new StringRedisSerializer());redisTemplate.setValueSerializer(new GenericJackson2JsonRedisSerializer());redisTemplate.setHashKeySerializer(new StringRedisSerializer());redisTemplate.setHashValueSerializer(new GenericJackson2JsonRedisSerializer());redisTemplate.afterPropertiesSet();return redisTemplate;}
}

最后 service 层的效果，简便多了是不是

@Autowired
private UserMapper userMapper;@Override
@MyRedisCacheAnnotation(keyPrefix="user", matchValue="#id")
public User getUserById(Integer id) {return userMapper.selectById(id);
}