一、概述

在实际的工作中，我们通常会使用多级缓存机制，将本地缓存和分布式缓存结合起来，从而提高系统性能和响应速度。本文通过springboot整合ehcache和redis实现多级缓存案例实战，从源码角度分析下多级缓存实现原理。

二、实战案例

1、pom依赖(注意引入cache和ehcache组件依赖)

<?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 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>org.example</groupId>
    <artifactId>cache-demo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <properties>
        <maven.compiler.source>8</maven.compiler.source>
        <maven.compiler.target>8</maven.compiler.target>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.0</version>
    </parent>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.4.3</version>
        </dependency>
        <dependency>
            <groupId>mysql</groupId>
            <artifactId>mysql-connector-java</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.2.1</version>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>fastjson</artifactId>
            <version>1.2.76</version>
        </dependency>
        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid</artifactId>
            <version>1.1.23</version>
        </dependency>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>23.0</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-redis</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-cache</artifactId>
        </dependency>
        <dependency>
            <groupId>net.sf.ehcache</groupId>
            <artifactId>ehcache</artifactId>
            <version>2.10.8</version>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-aop</artifactId>
        </dependency>
    </dependencies>
</project>

2、application.properties(启动类加上：@EnableCaching注解)

server.port = 7001
spring.application.name = cache-demo

#log config
logging.config = classpath:log/logback.xml
debug = false

#mp config
mybatis-plus.mapper-locations = classpath*:mapper/*.xml
mybatis-plus.configuration.log-impl = org.apache.ibatis.logging.stdout.StdOutImpl

spring.datasource.type = com.alibaba.druid.pool.DruidDataSource
spring.datasource.druid.driver-class-name = com.mysql.cj.jdbc.Driver
spring.datasource.url = jdbc:mysql://localhost:3306/数据库?characterEncoding=utf-8
spring.datasource.username = 数据库账号
spring.datasource.password = 数据库密码

#redis config
spring.redis.host = redis主机
spring.redis.port = 6379
spring.redis.password=redis密码，没有就删掉该配置

# ehcache config
spring.cache.type = ehcache
spring.cache.ehcache.config = classpath:ehcache.xml

3、ehcache.xml

<?xml version="1.0" encoding="UTF-8"?>
<ehcache xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:noNamespaceSchemaLocation="http://ehcache.org/ehcache.xsd"
         updateCheck="false">
    <diskStore path="D:\ehcache"/>

    <!--默认缓存策略 -->
    <!-- external：是否永久存在，设置为true则不会被清除，此时与timeout冲突，通常设置为false-->
    <!-- diskPersistent：是否启用磁盘持久化-->
    <!-- maxElementsInMemory：最大缓存数量-->
    <!-- overflowToDisk：超过最大缓存数量是否持久化到磁盘-->
    <!-- timeToIdleSeconds：最大不活动间隔，设置过长缓存容易溢出，设置过短无效果，单位：秒-->
    <!-- timeToLiveSeconds：最大存活时间，单位：秒-->
    <!-- memoryStoreEvictionPolicy：缓存清除策略-->
    <defaultCache
            eternal="false"
            diskPersistent="false"
            maxElementsInMemory="1000"
            overflowToDisk="false"
            timeToIdleSeconds="60"
            timeToLiveSeconds="60"
            memoryStoreEvictionPolicy="LRU"/>

    <cache
            name="studentCache"
            eternal="false"
            diskPersistent="false"
            maxElementsInMemory="1000"
            overflowToDisk="false"
            timeToIdleSeconds="100"
            timeToLiveSeconds="100"
            memoryStoreEvictionPolicy="LRU"/>
</ehcache>

4、MybatisPlusConfig类(注意：@MapperScan注解，也可加在启动类上)

@Configuration
@MapperScan("com.cache.demo.mapper")
public class MybatisPlusConfig {

    @Bean
    public MybatisPlusInterceptor mybatisPlusInterceptor() {
        //分页插件
        MybatisPlusInterceptor mybatisPlusInterceptor = new MybatisPlusInterceptor();
        mybatisPlusInterceptor.addInnerInterceptor(new PaginationInnerInterceptor());
        return mybatisPlusInterceptor;
    }
}

5、测试demo

这里可以将一级缓存、二级缓存时效设置短一些，方便进行测试。

@Slf4j
@RestController
@RequestMapping("/cache")
public class CacheController {

    @Resource
    private StudentMapper studentMapper;
    @Autowired
    private StringRedisTemplate stringRedisTemplate;

  	// 添加缓存注解(一级缓存：ehcache)
    @Cacheable(value = "studentCache", key = "#id+'getStudentById'")
    @GetMapping("/getStudentById")
    public String getStudentById(Integer id) {
        String key = "student:" + id;
      	// 一级缓存中不存在，则从二级缓存：redis中查找
        String studentRedis = stringRedisTemplate.opsForValue().get(key);
        if (StringUtils.isNotBlank(studentRedis)) {
            return JSON.toJSONString(JSON.parseObject(studentRedis, Student.class));
        }
        // 二级缓存中不存在则查询数据库，并更新二级缓存、一级缓存
        Student student = studentMapper.selectStudentById(id);
        if (null != student) {
            stringRedisTemplate.opsForValue().set(key, JSON.toJSONString(student));
        }
        return JSON.toJSONString(student);
    }
}

6、启动类上的：@EnableCaching注解

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Import(CachingConfigurationSelector.class)
public @interface EnableCaching {
  
	boolean proxyTargetClass() default false;
  
	AdviceMode mode() default AdviceMode.PROXY;
  
  int order() default Ordered.LOWEST_PRECEDENCE;
}

7、导入的：
CachingConfigurationSelector类：

public class CachingConfigurationSelector extends AdviceModeImportSelector<EnableCaching> {

	@Override
	public String[] selectImports(AdviceMode adviceMode) {
		switch (adviceMode) {
			case PROXY:
        // 此处走的是：PROXY
				return getProxyImports();
			case ASPECTJ:
				return getAspectJImports();
			default:
				return null;
		}
	}

	private String[] getProxyImports() {
		List<String> result = new ArrayList<>(3);
    // 导入了AutoProxyRegistrar类和ProxyCachingConfiguration类
		result.add(AutoProxyRegistrar.class.getName());
		result.add(ProxyCachingConfiguration.class.getName());
		if (jsr107Present && jcacheImplPresent) {
			result.add(PROXY_JCACHE_CONFIGURATION_CLASS);
		}
		return StringUtils.toStringArray(result);
	}
}

8、AutoProxyRegistrar类(代码有所简化)：

public class AutoProxyRegistrar implements ImportBeanDefinitionRegistrar {

	private final Log logger = LogFactory.getLog(getClass());

	@Override
	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
				// 最终注册了：InfrastructureAdvisorAutoProxyCreator(BeanPostProcessor接口实现类)
    		// 通过重写postProcessAfterInitialization接口创建代理对象
      	AopConfigUtils.registerAutoProxyCreatorIfNecessary(registry);
	}
}

@Nullable
	public static BeanDefinition registerAutoProxyCreatorIfNecessary(BeanDefinitionRegistry registry, @Nullable Object source) {
		return registerOrEscalateApcAsRequired(InfrastructureAdvisorAutoProxyCreator.class, registry, source);
	}

9、导入的第一个类看完了，接着看导入的第二个类：ProxyCachingConfiguration

@Configuration(proxyBeanMethods = false)
@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
public class ProxyCachingConfiguration extends AbstractCachingConfiguration {

	@Bean(name = CacheManagementConfigUtils.CACHE_ADVISOR_BEAN_NAME)
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public BeanFactoryCacheOperationSourceAdvisor cacheAdvisor(CacheOperationSource cacheOperationSource, CacheInterceptor cacheInterceptor) {
		//  构建BeanFactoryCacheOperationSourceAdvisor
    BeanFactoryCacheOperationSourceAdvisor advisor = new BeanFactoryCacheOperationSourceAdvisor();
		// 设置缓存注解解析器
    advisor.setCacheOperationSource(cacheOperationSource);
		// 设置缓存拦截器：cacheInterceptor
    advisor.setAdvice(cacheInterceptor);
		if (this.enableCaching != null) {
			advisor.setOrder(this.enableCaching.<Integer>getNumber("order"));
		}
		return advisor;
	}

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public CacheOperationSource cacheOperationSource() {
    // 缓存注解解析器
		return new AnnotationCacheOperationSource();
	}

	@Bean
	@Role(BeanDefinition.ROLE_INFRASTRUCTURE)
	public CacheInterceptor cacheInterceptor(CacheOperationSource cacheOperationSource) {
		// 缓存拦截器
    CacheInterceptor interceptor = new CacheInterceptor();
		interceptor.configure(this.errorHandler, this.keyGenerator, this.cacheResolver, this.cacheManager);
		interceptor.setCacheOperationSource(cacheOperationSource);
		return interceptor;
	}
}

10、继续看下CacheInterceptor类(重要)：

public class CacheInterceptor extends CacheAspectSupport implements MethodInterceptor, Serializable {

	@Override
	@Nullable
	public Object invoke(final MethodInvocation invocation) throws Throwable {
		Method method = invocation.getMethod();
		CacheOperationInvoker aopAllianceInvoker = () -> {
			try {
				return invocation.proceed();
			}
			catch (Throwable ex) {
				throw new CacheOperationInvoker.ThrowableWrapper(ex);
			}
		};

		Object target = invocation.getThis();
		Assert.state(target != null, "Target must not be null");
		try {
      // 缓存执行逻辑
			return execute(aopAllianceInvoker, target, method, invocation.getArguments());
		}
		catch (CacheOperationInvoker.ThrowableWrapper th) {
			throw th.getOriginal();
		}
	}
}

@Nullable
	protected Object execute(CacheOperationInvoker invoker, Object target, Method method, Object[] args) {
		if (this.initialized) {
			Class<?> targetClass = getTargetClass(target);
			CacheOperationSource cacheOperationSource = getCacheOperationSource();
			if (cacheOperationSource != null) {
        // 解析缓存相关注解，返回CacheOperation
        // 每个缓存注解对应一种不同的解析处理操作
        // CacheEvictOperation、CachePutOperation、CacheableOperation等
				Collection<CacheOperation> operations = cacheOperationSource.getCacheOperations(method, targetClass);
				if (!CollectionUtils.isEmpty(operations)) {
          // 执行缓存逻辑
					return execute(invoker, method,
							new CacheOperationContexts(operations, method, args, target, targetClass));
				}
			}
		}
		return invoker.invoke();
	}

private Object execute(final CacheOperationInvoker invoker, Method method, CacheOperationContexts contexts) {
		// 解析处理@CacheEvict注解
    processCacheEvicts(contexts.get(CacheEvictOperation.class), true,	CacheOperationExpressionEvaluator.NO_RESULT);

		// 解析处理@Cacheable注解
		Cache.ValueWrapper cacheHit = findCachedItem(contexts.get(CacheableOperation.class));

		List<CachePutRequest> cachePutRequests = new ArrayList<>();
		if (cacheHit == null) {
			collectPutRequests(contexts.get(CacheableOperation.class),	CacheOperationExpressionEvaluator.NO_RESULT, cachePutRequests);
		}

		Object cacheValue;
		Object returnValue;

		if (cacheHit != null && !hasCachePut(contexts)) {
			// 命中缓存，则从缓存中获取数据
			cacheValue = cacheHit.get();
			returnValue = wrapCacheValue(method, cacheValue);
		} else {
			// 未命中缓存，则通过反射执行目标方法
			returnValue = invokeOperation(invoker);
			cacheValue = unwrapReturnValue(returnValue);
		}

		// 解析处理@CachePut注解
		collectPutRequests(contexts.get(CachePutOperation.class), cacheValue, cachePutRequests);

		// 未命中缓存时，会封装一个cachePutRequests
  	// 然后通过反射执行目标方法后，执行该方法，最终调用EhCacheCache.put方法将数据写入缓存中
		for (CachePutRequest cachePutRequest : cachePutRequests) {
			cachePutRequest.apply(cacheValue);
		}
		// 解析处理@CacheEvict注解，和上面的方法相同，只不过第二个参数不同
		processCacheEvicts(contexts.get(CacheEvictOperation.class), false, cacheValue);
		return returnValue;
	}

11、接着看下findCachedItem方法

private Cache.ValueWrapper findCachedItem(Collection<CacheOperationContext> contexts) {
		Object result = CacheOperationExpressionEvaluator.NO_RESULT;
		for (CacheOperationContext context : contexts) {
			if (isConditionPassing(context, result)) {
        // 生成key策略：解析@Cacheable注解中的key属性
        // 若未配置则默认使用SimpleKeyGenerator#generateKey方法生成key
				Object key = generateKey(context, result);
				Cache.ValueWrapper cached = findInCaches(context, key);
				if (cached != null) {
					return cached;
				}	else {
					if (logger.isTraceEnabled()) {
						logger.trace("No cache entry for key '" + key + "' in cache(s) " + context.getCacheNames());
					}
				}
			}
		}
		return null;
	}

// SimpleKeyGenerator#generateKey
public static Object generateKey(Object... params) {
  	// 方法没有参数，则返回空的SimpleKey
		if (params.length == 0) {
			return SimpleKey.EMPTY;
		}
  	// 方法参数只有一个，则返回该参数
		if (params.length == 1) {
			Object param = params[0];
			if (param != null && !param.getClass().isArray()) {
				return param;
			}
		}
  	// 否则将方法参数进行封装，返回SimpleKey
		return new SimpleKey(params);
	}

private Cache.ValueWrapper findInCaches(CacheOperationContext context, Object key) {
		for (Cache cache : context.getCaches()) {
      // 从一级缓存中获取数据
			Cache.ValueWrapper wrapper = doGet(cache, key);
			if (wrapper != null) {
				if (logger.isTraceEnabled()) {
					logger.trace("Cache entry for key '" + key + "' found in cache '" + cache.getName() + "'");
				}
				return wrapper;
			}
		}
		return null;
	}

protected Cache.ValueWrapper doGet(Cache cache, Object key) {
		try {
      // 这里我们使用的是：EhCacheCache，所以最终会调用EhCacheCache.get方法获取缓存中的数据
			return cache.get(key);
		}
		catch (RuntimeException ex) {
			getErrorHandler().handleCacheGetError(ex, cache, key);
			return null;
		}
	}

三、总结

@EnableCaching和@Transactional等实现逻辑大体相同，看的多了，则一通百通。