原 荐 SpringBoot,用200行代码完成一个一二级分布式缓存

     缓存系统的用来代替直接访问数据库,用来提升系统性能,减小数据库复杂。早期缓存跟系统在一个虚拟机里,这样内存访问,速度最快。 后来应用系统水平扩展,缓存作为一个独立系统存在,如redis,但是每次从缓存获取数据,都还是要通过网络访问才能获取,效率相对于早先从内存里获取,还是差了点。如果一个应用,比如传统的企业应用,一次页面显示,要访问数次redis,那效果就不是特别好,因此,现在有人提出了一二级缓存。即一级缓存跟系统在一个虚拟机内,这样速度最快。二级缓存位于redis里,当一级缓存没有数据的时候,再从redis里获取,并同步到一级缓存里。

现在实现这种一二级缓存的也挺多的,比如 hazelcast,新版的Ehcache..不过,实际上,如果你用spring boot,手里又一个Redis,则不需要搞hazelcastEhcache,只需要200行代码,就能在spring boot基础上,提供一个一二级缓存,代码如下:


import java.io.UnsupportedEncodingException;
import java.util.concurrent.ConcurrentHashMap;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.boot.autoconfigure.AutoConfigureBefore;
import org.springframework.boot.bind.RelaxedPropertyResolver;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Condition;
import org.springframework.context.annotation.ConditionContext;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.type.AnnotatedTypeMetadata;
import org.springframework.data.redis.cache.RedisCache;
import org.springframework.data.redis.cache.RedisCacheManager;
import org.springframework.data.redis.cache.RedisCachePrefix;
import org.springframework.data.redis.connection.Message;
import org.springframework.data.redis.connection.MessageListener;
import org.springframework.data.redis.connection.RedisConnectionFactory;
import org.springframework.data.redis.core.RedisOperations;
import org.springframework.data.redis.core.RedisTemplate;
import org.springframework.data.redis.listener.PatternTopic;
import org.springframework.data.redis.listener.RedisMessageListenerContainer;
import org.springframework.data.redis.listener.adapter.MessageListenerAdapter;



@Configuration
@Conditional(StarterCacheCondition.class)
public class CacheConfig {
	
	@Value("${springext.cache.redis.topic:cache}")
	String topicName ;
	
	
	
	@Bean
	public MyRedisCacheManager cacheManager(RedisTemplate<Object, Object> redisTemplate) {
		MyRedisCacheManager cacheManager = new MyRedisCacheManager(redisTemplate);
		cacheManager.setUsePrefix(true);
		return cacheManager;
	}

@Bean
    RedisMessageListenerContainer container(RedisConnectionFactory connectionFactory,
            MessageListenerAdapter listenerAdapter) {

        RedisMessageListenerContainer container = new RedisMessageListenerContainer();
        container.setConnectionFactory(connectionFactory);
        container.addMessageListener(listenerAdapter, new PatternTopic(topicName));

        return container;
    }

    @Bean
    MessageListenerAdapter listenerAdapter(MyRedisCacheManager cacheManager ) {
        return new MessageListenerAdapter(new MessageListener(){

			@Override
			public void onMessage(Message message, byte[] pattern) {
				byte[] bs = message.getChannel();
				try {
					String type = new String(bs,"UTF-8");
					cacheManager.receiver(type);
				} catch (UnsupportedEncodingException e) {
					e.printStackTrace();
					// 不可能出错
				}
			
				
				
			}
        	
        });
    }
	
	
	
	class MyRedisCacheManager extends RedisCacheManager{
		
		
		public MyRedisCacheManager(RedisOperations redisOperations) {
			super(redisOperations);
			
		}
		
		
		@SuppressWarnings("unchecked")
		@Override
		protected RedisCache createCache(String cacheName) {
			long expiration = computeExpiration(cacheName);
			return new MyRedisCache(this,cacheName, (this.isUsePrefix()? this.getCachePrefix().prefix(cacheName) : null), this.getRedisOperations(), expiration);
		}
		
		/**
		 * get a messsage for update cache
		 * @param cacheName
		 */
		public void receiver(String cacheName){
			MyRedisCache cache = (MyRedisCache)this.getCache(cacheName);
			if(cache==null){
				return ;
			}
			cache.cacheUpdate();
			
		}
		
		//notify other redis clent to update cache( clear local cache in fact)
		public void publishMessage(String cacheName){
			this.getRedisOperations().convertAndSend(topicName, cacheName);
		}
		
	}
	
	class MyRedisCache extends RedisCache{
		//local cache for performace
		ConcurrentHashMap<Object,ValueWrapper> local = new ConcurrentHashMap<>();
		MyRedisCacheManager cacheManager;
		public MyRedisCache(MyRedisCacheManager cacheManager,String name, byte[] prefix,
				RedisOperations<? extends Object, ? extends Object> redisOperations, long expiration) {
			super(name, prefix, redisOperations, expiration);
			this.cacheManager = cacheManager;
		}
		@Override
		public ValueWrapper get(Object key) {
			ValueWrapper wrapper = local.get(key);
			if(wrapper!=null){
				return wrapper;
			}else{
				wrapper =   super.get(key);
				if(wrapper!=null){
					local.put(key, wrapper);
				}
				
				return wrapper;
			}
			
		}
		
		@Override
		public void put(final Object key, final Object value) {

			super.put(key, value);
			cacheManager.publishMessage(super.getName());
		}
		
		@Override
		public void evict(Object key) {
			super.evict(key);
			cacheManager.publishMessage(super.getName());
		}
		
		
		@Override
		public ValueWrapper putIfAbsent(Object key, final Object value){
			ValueWrapper wrapper = super.putIfAbsent(key, value);
			cacheManager.publishMessage(super.getName());
			return wrapper;
		}
		
		public void cacheUpdate(){
			//clear all cache for simplification 
			local.clear();
		}
		
	}
	

}

class StarterCacheCondition implements Condition {

	
	@Override
	public boolean matches(ConditionContext context, AnnotatedTypeMetadata metadata) {
		RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(
				context.getEnvironment(), "springext.cache.");
		
		String env = resolver.getProperty("type");
		if(env==null){
			return false;
		}
		return "local2redis".equalsIgnoreCase(env.toLowerCase());
	
	}

}

代码的核心在于spring boot提供一个概念CacheManager&Cache用来表示缓存,并提供了多达8种实现,但由于缺少一二级缓存,因此,需要在Redis基础上扩展,因此实现了MyRedisCacheManger,以及MyRedisCache,增加一个本地缓存。

一二级缓存需要解决的的一个问题是缓存更新的时候,必须通知其他节点的springboot应用缓存更新。这里可以用Redis的 Pub/Sub 功能来实现,具体可以参考listenerAdapter方法实现。

使用的时候,需要配置如下,这样,就可以使用缓存了,性能杠杠的好

 

springext.cache.type=local2redis

# Redis服务器连接端口
spring.redis.host=172.16.86.56
spring.redis.port=6379  

 

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