Spring 之 @Cacheable 缓存使用教程

本文介绍: 该抽象类提供 loadCa ch es() 方法，可以获取到所有 Ca ch e 接口实现类。所以这里能够获取到所有缓存。那么肯定是可以使用双缓存。/*** 直接实现 Ab str a ctCac heMana g e r 抽象类的钩子方法，该类已经写好模版方法* 当执行的时候，如果 MyGua vaCac h eMana g e r 管理类 @Be a n 的话，就会勾到这个方法逻辑* @return*/@Ov err ide@Overr ide@Overr ide@Re source@Be a n@Bea n。

定义个 Con t roller ，在方法上加上注解 @Cacheable，配置要使用哪些缓存，比如 myMapCac he 表示一级缓存是 Map，myRedi sCac he 表示二级缓存是 Redis。并配置缓存 key。 key 由 SPEL 表达式组成，Spr in g 可以动态解析生成缓存 key。

@RestController
public class CachingAnnoController {

	@Cacheable(cacheNames = {"myMapCache","myRedisCache"},key = "'test_'+#key")
	@RequestMapping("/cachingAnno")
	public String cachingAnno(String key,String value){
		System.out.println("查询数据库值 = " + value);
		return "value";
	}
}

用过 @Cacheable 注解的都知道，要开启缓存功能必须通过 @EnableCaching 注解。代码如下：

@ComponentScan(value = "com.gwm")
@Configuration
@EnableCaching
public class SpringConfig {

}

上述 @EnableCaching、@Cacheable 都是 Spring 提供的基本缓存框架，而具体的缓存需要自己引入。比如现在自己定义两个缓存：MyMapCache 类、MyRedisCache 类。然后实现接口方法。

public class MyMapCache implements Cache {

	public static final Map&lt;Object, Object&gt; map = new ConcurrentHashMap&lt;>();

	private String cacheName;

	public MyMapCache(String cacheName) {
		this.cacheName = cacheName;
	}

	@Override
	public String getName() {
		return cacheName;
	}

	@Override
	public Object getNativeCache() {
		return null;
	}

	@Override
	public ValueWrapper get(Object key) {
		System.out.println(">>>>>>我是 MyMapCache 缓存中的 get() 方法");
		Object o = map.get(key);
		if (Objects.nonNull(o)) {
			return new SimpleValueWrapper(o);
		}
		return null;
	}

	@Override
	public <T> T get(Object key, Class<T> type) {

		return (T)map.get(key);
	}

	@Override
	public <T> T get(Object key, Callable<T> valueLoader) {
		return (T)map.get(key);
	}

	@Override
	public void put(Object key, Object value) {
		System.out.println(">>>>>>我是 MyMapCache 缓存中的 put() 方法");
		map.put(key, value);
	}

	@Override
	public void evict(Object key) {
		map.remove(key);
	}

	@Override
	public void clear() {
		map.clear();
	}
}

MyRedisCache 类实现，代码如下：

public class MyRedisCache implements Cache {

	private String cacheName;
	private RedisTemplate<Object,Object> redisTemplate;

	public MyRedisCache(String cacheName, RedisTemplate<Object, Object> redisTemplate) {
		this.cacheName = cacheName;
		this.redisTemplate = redisTemplate;
	}

	@Override
	public String getName() {
		return cacheName;
	}

	@Override
	public Object getNativeCache() {
		return this;
	}

	@Override
	public ValueWrapper get(Object key) {
		System.out.println(">>>>>>我是 MyRedisCache 缓存中的 get() 方法");
		Object o = redisTemplate.opsForValue().get(key);
		if (Objects.nonNull(o)) {
			return new SimpleValueWrapper(o);
		}

		return null;
	}

	@Override
	public <T> T get(Object key, Class<T> type) {
		return null;
	}

	@Override
	public <T> T get(Object key, Callable<T> valueLoader) {
		return null;
	}

	@Override
	public void put(Object key, Object value) {
		System.out.println(">>>>>>我是 MyRedisCache 缓存中的 put() 方法");
		redisTemplate.opsForValue().set(key,value);
		redisTemplate.expire(key, Duration.ofMillis(3000));
	}

	@Override
	public void evict(Object key) {
		redisTemplate.delete(key);
	}

	@Override
	public void clear() {
		redisTemplate.execute((RedisCallback<Object>) conn->{

			// 清空所有缓存数据，要格外注意这个操作，很危险
			conn.flushDb();

			return ">>>>>>flush db success!";
		});
	}
}

自定义缓存定义完之后，光摆在这里肯定是不能起作用的，还需要借助 Spring 标准化接口 CacheManager 类来把缓存加入到缓存切面逻辑中。

比如实现 MyMapCache 缓存管理类 MyMapCacheManager，代码如下：

public class MyMapCacheManager implements CacheManager {

	@Override
	public Cache getCache(String name) {
		return new MyMapCache(name);
	}

	@Override
	public Collection<String> getCacheNames() {
		return Arrays.asList("myMapCache");
	}
}

public class MyRedisCacheManager implements CacheManager {

	@Override
	public Cache getCache(String name) {
		return new MyRedisCache(name,redisTemplate);
	}

	@Override
	public Collection<String> getCacheNames() {
		return Arrays.asList("myRedisCache");
	}
}

@Configuration
public class MyRedisMainConfig {

	@Resource
	private RedisTemplate<Object,Object> redisTemplate;

	@Bean
	public MyMapCache myMapCache() {
		MyMapCache myMapCache = new MyMapCache("myMapCache");
		return myMapCache;
	}
	
	@Bean
	public MyRedisCache myRedisCache() {
		MyRedisCache myRedisCache = new MyRedisCache("myRedisCache",redisTemplate);

		return myRedisCache;
	}
	
	@Bean
	public MyRedisCacheManager cacheManager() {
		MyRedisCacheManager redisCacheManager = new MyRedisCacheManager();
		return redisCacheManager;
	}
	
	// @Bean 
	public MyMapCacheManager cacheManager() {
		MyRedisCacheManager redisCacheManager = new MyRedisCacheManager();
		return redisCacheManager;
	}
	
}

public class MySimpleCacheManager extends AbstractCacheManager implements ApplicationContextAware {

	private static final List<Cache> list = new ArrayList<>();

	private ApplicationContext context;
	/**
	 * 直接实现 AbstractCacheManager 抽象类的钩子方法，该类已经写好模版方法
	 * 当执行的时候，如果 MyGuavaCacheManager 管理类 @Bean 的话，就会勾到这个方法逻辑
	 * @return
	 */
	@Override
	protected Collection<? extends Cache> loadCaches() {
		return list;
	}

	@Override
	public void afterPropertiesSet() {
		Map<String, Cache> beansOfType = context.getBeansOfType(Cache.class);
		list.addAll(beansOfType.values());
	}

	@Override
	public void setApplicationContext(ApplicationContext applicationContext) throws BeansException 
		this.context = applicationContext;
	}
}

@Configuration
public class MyRedisMainConfig {

	@Resource
	private RedisTemplate<Object,Object> redisTemplate;

	@Bean
	public MyMapCache myMapCache() {
		MyMapCache myMapCache = new MyMapCache("myMapCache");
		return myMapCache;
	}
	
	@Bean
	public MyRedisCache myRedisCache() {
		MyRedisCache myRedisCache = new MyRedisCache("myRedisCache",redisTemplate);
		return myRedisCache;
	}
	
	@Bean
	public MySimpleCacheManager cacheManager(@Qualifier("myMapCache") MyMapCache myMapCache,
												 @Qualifier("myRedisCache") MyRedisCache myRedisCache,
												 @Qualifier("myGuavaCache") MyGuavaCache myGuavaCache) {
												 
		SimpleCacheManager simpleCacheManager = new SimpleCacheManager();
		simpleCacheManager.setCaches(Arrays.asList(myMapCache,myRedisCache,myGuavaCache));
		return simpleCacheManager;
	}
}