guava cache與spring集成

緩存的背景

    緩存，在咱們平常開發中是必不可少的一種解決性能問題的方法。簡單的說，cache 就是爲了提高系統性能而開闢的一塊內存空間。在cpu進行計算的時候， 首先是讀取寄存器，而後內存，再是硬盤。因爲寄存器容量很小，不太適合存儲咱們須要快速讀取的數據，放在硬盤中話，效率過低，因此大多數人將一些靜態資源或者不常常修改的數據放在內存中。 　

緩存的做用

    緩存的主要做用是暫時在內存中保存業務系統的數據處理結果，而且等待下次訪問使用。在平常開發的不少場合，因爲受限於硬盤 IO的性能或者咱們自身業務系統的數據處理和獲取可能很是費時，當咱們發現咱們的系統這個數據請求量很大的時候，頻繁的IO和頻繁的 邏輯處理會致使硬盤和CPU資源的瓶頸出現。緩存的做用就是將這些來自不易的數據保存在內存中，當有其餘線程或者客戶端須要查詢相同 的數據資源時，直接從緩存的內存塊中返回數據，這樣不但能夠提升系統的響應時間，同時也能夠節省對這些數據的處理流程的資源消耗，總體上來講，系統性能會有大大的提高。

guava cache與spring整合

    你們都清楚，相對於靜態Map實現本地緩存而言guava cache提供了許多種對緩存管理策略，好比：緩存個數、緩存生存期、緩存提取策略（LRU）等, 也正是這樣，guava cache在本地緩存層面上使用是開發人員的首選。而在企業開發中spring是用的最多的，若是將guava cache與spring整合，依靠spring強大的IOC和AOP在使用緩存時是很方便、 快捷的，而要實現spring與guava cache整合 只須要如下三個步驟就能夠搞定：

創建spring-cache.xml

    首先創建spring-cache.xml 裏面配置spring對guava cache基本參數的管理，以下：

<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:c="http://www.springframework.org/schema/c" xmlns:p="http://www.springframework.org/schema/p" xmlns:cache="http://www.springframework.org/schema/cache" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/cache http://www.springframework.org/schema/cache/spring-cache-4.0.xsd"> <!--啓動註解 進行guava cache 管理--> <cache:annotation-driven cache-manager="cacheManager" proxy-target-class="true"/> <bean id="cacheManager" class="org.springframework.cache.support.CompositeCacheManager"> <property name="cacheManagers"> <list> <!--將guava cache交於spring管理 若是要實現redis 也能夠加在這裏--> <ref bean="guavaCacheManager"/> </list> </property> <property name="fallbackToNoOpCache" value="true"/> </bean> <!--配置guava cache須要緩存的key 以及創建方式--> <bean id="guavaCacheManager" class="com.daojia.open.confluence.worker.common.GuavaCacheManager"> <property name="configMap"> <map key-type="java.lang.String" value-type="com.google.common.cache.CacheBuilder"> <entry key="indexReptileKeyValue" value-ref="defaultCacheBuilder"/> </map> </property> </bean> <!--設置guava cache緩存策略 生存期爲24小時 最大100個緩存數--> <bean id="defaultCacheBuilder" class="com.google.common.cache.CacheBuilder" factory-method="from"> <constructor-arg value="maximumSize=100, expireAfterWrite=24h"/> </bean> </beans> 

實現spring對外提供的接口

    上面配置了將guavaCacheManager交於spring管理，那麼久要實現這個管理類，該類若是要被spring容器管理的話須要 實現AbstractTransactionSupportingCacheManager接口，該接口支持事物回滾，當緩存失敗，會將錯誤數據還原。具體實現以下：

package com.daojia.open.confluence.worker.common; import com.google.common.cache.CacheBuilder; import com.google.common.collect.Maps; import org.springframework.cache.Cache; import org.springframework.cache.transaction.AbstractTransactionSupportingCacheManager; import java.util.Collection; import java.util.Map; import java.util.concurrent.ConcurrentMap; /** * guavacache支持事務回滾，重寫manager。 * cache的構建使用builder配置構建 */ public class GuavaCacheManager extends AbstractTransactionSupportingCacheManager { private final ConcurrentMap<String, Cache> cacheMap = Maps.newConcurrentMap(); private boolean dynamic = true; private Map<String, CacheBuilder> builderMap = Maps.newHashMap(); private boolean allowNullValues = true; @Override protected Collection<? extends Cache> loadCaches() { Collection<Cache> values = cacheMap.values(); return values; } @Override public Cache getCache(String name) { Cache cache = this.cacheMap.get(name); if (cache == null && this.dynamic) { synchronized (this.cacheMap) { cache = this.cacheMap.get(name); if (cache == null && this.builderMap.containsKey(name)) { CacheBuilder builder = this.builderMap.get(name); cache = createGuavaCache(name, builder); this.cacheMap.put(name, cache); } } } return cache; } protected Cache createGuavaCache(String name, CacheBuilder builder) { com.google.common.cache.Cache<Object, Object> cache = null; if(builder == null){ cache = CacheBuilder.newBuilder().build(); }else{ cache = builder.build(); } return new GuavaCache(name, cache, isAllowNullValues()); } public boolean isAllowNullValues() { return this.allowNullValues; } public void setConfigMap(Map<String, CacheBuilder> configMap) { this.builderMap = configMap; } } 

    這僅僅是對guava cache管理 還須要一個具體的緩存操做類，該類也是同樣要被spring管理，要實現一個cache接口，該接口是spring對外緩存管理的統一接口，只要實現該 接口的緩存，都能被spring管理起來，好比guava cache 以下：

package com.daojia.open.confluence.worker.common; import com.daojia.open.confluence.worker.utils.JsonMapper; import org.slf4j.Logger; import org.slf4j.LoggerFactory; import org.springframework.cache.Cache; import org.springframework.cache.support.SimpleValueWrapper; import org.springframework.util.Assert; import java.io.Serializable; import java.util.concurrent.Callable; import java.util.concurrent.ExecutionException; public class GuavaCache implements Cache { private static Logger log = LoggerFactory.getLogger(GuavaCache.class); private final JsonMapper mapper = new JsonMapper(); private static final Object NULL_HOLDER = new NullHolder(); private final String name; private final com.google.common.cache.Cache<Object, Object> cache; private final boolean allowNullValues; public GuavaCache(String name, com.google.common.cache.Cache<Object, Object> cache) { this(name, cache, true); } public GuavaCache(String name, com.google.common.cache.Cache<Object, Object> cache, boolean allowNullValues) { Assert.notNull(name, "Name must not be null"); Assert.notNull(cache, "Cache must not be null"); this.name = name; this.cache = cache; this.allowNullValues = allowNullValues; } @Override public String getName() { return this.name; } @Override public Object getNativeCache() { return this.cache; } @Override public ValueWrapper get(Object key) { key = getKey(key.toString()); Object value = this.cache.getIfPresent(key); log.info("獲取緩存key={},獲取對象={}", key, mapper.toJson(value)); return toWrapper(value); } @Override public <T> T get(Object key, Class<T> type) { key = getKey(key.toString()); Object value = fromStoreValue(this.cache.getIfPresent(key)); log.info("獲取緩存key={},獲取對象={}", key, mapper.toJson(value)); if (value != null && type != null && !type.isInstance(value)) { throw new IllegalStateException("Cached value is not of required type [" + type.getName() + "]: " + value); } return (T) value; } @Override public void put(Object key, Object value) { key = getKey(key.toString()); this.cache.put(key, toStoreValue(value)); log.info("存入緩存key=={},存入對象={}", key, mapper.toJson(value)); } @Override public ValueWrapper putIfAbsent(Object key, Object value) { try { PutIfAbsentCallable callable = new PutIfAbsentCallable(value); Object result = this.cache.get(key, callable); return (callable.called ? null : toWrapper(result)); } catch (ExecutionException ex) { throw new IllegalStateException(ex); } } @Override public void evict(Object key) { this.cache.invalidate(key); log.info("刪除緩存key={}",key); } @Override public void clear() { this.cache.invalidateAll(); log.info("清空guavacache全部緩存"); } private ValueWrapper toWrapper(Object value) { return (value != null ? new SimpleValueWrapper(fromStoreValue(value)) : null); } protected Object fromStoreValue(Object storeValue) { if (this.allowNullValues && storeValue == NULL_HOLDER) { return null; } return storeValue; } public final boolean isAllowNullValues() { return this.allowNullValues; } @SuppressWarnings("serial") private static class NullHolder implements Serializable { } protected Object toStoreValue(Object userValue) { if (this.allowNullValues && userValue == null) { return NULL_HOLDER; } return userValue; } private class PutIfAbsentCallable implements Callable<Object> { private final Object value; private boolean called; public PutIfAbsentCallable(Object value) { this.value = value; } @Override public Object call() throws Exception { this.called = true; return toStoreValue(this.value); } } /**實現key增長cache名稱**/ private String getKey(String key) { return name + "_" + key; } } 

編寫sqel語法 對緩存進行管理

    當完成這上面兩個步驟以後，代表你的guava cache已被spring管理起來了，這時能夠熟悉一下sqel註釋語法，這是spring 對緩存進行註解管理用到經常使用語法，好比獲取緩存：

/*當使用到該方法的時候 spring會首先判斷緩存中是否含有該key的值 ，若是有則從本地緩存中獲取 並以你輸入的參數indexReptileKey爲key獲取，不然從執行方法體中的獲取 並將獲取的數據放入到緩存中*/ @Cacheable(value = "indexReptileKeyValue", key = "#indexReptileKey") public List<IndexReptilePJO> getReptile(int indexReptileKey) throws Exception { LOGGER.info("不走guava cache獲取參數"); return super.handlerindexReptile(); } 

    放入緩存以下:

/*設置某個值的時候，想將該值存入緩存 則用這個註解 將你須要設置的值設置到緩存中 另外一個方法在獲取的時候就是從緩存中獲取*/ @CachePut(value = "indexReptileKeyValue", key = "#indexReptileKey") public List<IndexReptilePJO> setReptile(int indexReptileKey) throws Exception { LOGGER.info("將樹節點項目路徑 存入guava cache中"); return super.handlerindexReptile(); }