缓存是在web开发中经常用到的，将程序经常使用到或调用到的对象存在内存中，或者是耗时较长但又不具有实时性的查询数据放入内存中，在一定程度上可以提高性能和效率。下面我实现了一个简单的缓存，步骤如下。
创建缓存对象EntityCache.java
public class EntityCache { /** * 保存的数据 */ private Object datas; /** * 设置数据失效时间,为0表示永不失效 */ private long timeOut; /** * 最后刷新时间 */ private long lastRefeshTime; public EntityCache(Object datas, long timeOut, long lastRefeshTime) { this.datas = datas; this.timeOut = timeOut; this.lastRefeshTime = lastRefeshTime; } public Object getDatas() { return datas; } public void setDatas(Object datas) { this.datas = datas; } public long getTimeOut() { return timeOut; } public void setTimeOut(long timeOut) { this.timeOut = timeOut; } public long getLastRefeshTime() { return lastRefeshTime; } public void setLastRefeshTime(long lastRefeshTime) { this.lastRefeshTime = lastRefeshTime; }}定义缓存操作接口，ICacheManager.java
public interface ICacheManager { /** * 存入缓存 * @param key * @param cache */ void putCache(String key, EntityCache cache); /** * 存入缓存 * @param key * @param cache */ void putCache(String key, Object datas, long timeOut); /** * 获取对应缓存 * @param key * @return */ EntityCache getCacheByKey(String key); /** * 获取对应缓存 * @param key * @return */ Object getCacheDataByKey(String key); /** * 获取所有缓存 * @param key * @return */ Map<String, EntityCache> getCacheAll(); /** * 判断是否在缓存中 * @param key * @return */ boolean isContains(String key); /** * 清除所有缓存 */ void clearAll(); /** * 清除对应缓存 * @param key */ void clearByKey(String key); /** * 缓存是否超时失效 * @param key * @return */ boolean isTimeOut(String key); /** * 获取所有key * @return */ Set<String> getAllKeys();}实现接口ICacheManager，CacheManagerImpl.java
这里我使用了ConcurrentHashMap来保存缓存，本来以为这样就是线程安全的，其实不然，在后面的测试中会发现它并不是线程安全的。
public class CacheManagerImpl implements ICacheManager { private static Map<String, EntityCache> caches = new ConcurrentHashMap<String, EntityCache>(); /** * 存入缓存 * @param key * @param cache */ public void putCache(String key, EntityCache cache) { caches.put(key, cache); } /** * 存入缓存 * @param key * @param cache */ public void putCache(String key, Object datas, long timeOut) { timeOut = timeOut > 0 ? timeOut : 0L; putCache(key, new EntityCache(datas, timeOut, System.currentTimeMillis())); } /** * 获取对应缓存 * @param key * @return */ public EntityCache getCacheByKey(String key) { if (this.isContains(key)) { return caches.get(key); } return null; } /** * 获取对应缓存 * @param key * @return */ public Object getCacheDataByKey(String key) { if (this.isContains(key)) { return caches.get(key).getDatas(); } return null; } /** * 获取所有缓存 * @param key * @return */ public Map<String, EntityCache> getCacheAll() { return caches; } /** * 判断是否在缓存中 * @param key * @return */ public boolean isContains(String key) { return caches.containsKey(key); } /** * 清除所有缓存 */ public void clearAll() { caches.clear(); } /** * 清除对应缓存 * @param key */ public void clearByKey(String key) { if (this.isContains(key)) { caches.remove(key); } } /** * 缓存是否超时失效 * @param key * @return */ public boolean isTimeOut(String key) { if (!caches.containsKey(key)) { return true; } EntityCache cache = caches.get(key); long timeOut = cache.getTimeOut(); long lastRefreshTime = cache.getLastRefeshTime(); if (timeOut == 0 || System.currentTimeMillis() - lastRefreshTime >= timeOut) { return true; } return false; } /** * 获取所有key * @return */ public Set<String> getAllKeys() { return caches.keySet(); }}CacheListener.java,监听失效数据并移除。
public class CacheListener{ Logger logger = Logger.getLogger("cacheLog"); private CacheManagerImpl cacheManagerImpl; public CacheListener(CacheManagerImpl cacheManagerImpl) { this.cacheManagerImpl = cacheManagerImpl; } public void startListen() { new Thread(){ public void run() { while (true) { for(String key : cacheManagerImpl.getAllKeys()) { if (cacheManagerImpl.isTimeOut(key)) { cacheManagerImpl.clearByKey(key); logger.info(key + "缓存被清除"); } } } } }.start(); }}测试类TestCache.java
public class TestCache { Logger logger = Logger.getLogger("cacheLog"); /** * 测试缓存和缓存失效 */ @Test public void testCacheManager() { CacheManagerImpl cacheManagerImpl = new CacheManagerImpl(); cacheManagerImpl.putCache("test", "test", 10 * 1000L); cacheManagerImpl.putCache("myTest", "myTest", 15 * 1000L); CacheListener cacheListener = new CacheListener(cacheManagerImpl); cacheListener.startListen(); logger.info("test:" + cacheManagerImpl.getCacheByKey("test").getDatas()); logger.info("myTest:" + cacheManagerImpl.getCacheByKey("myTest").getDatas()); try { TimeUnit.SECONDS.sleep(20); } catch (InterruptedException e) { e.printStackTrace(); } logger.info("test:" + cacheManagerImpl.getCacheByKey("test")); logger.info("myTest:" + cacheManagerImpl.getCacheByKey("myTest")); } /** * 测试线程安全 */ @Test public void testThredSafe() { final String key = "thread"; final CacheManagerImpl cacheManagerImpl = new CacheManagerImpl(); ExecutorService exec = Executors.newCachedThreadPool(); for (int i = 0; i < 100; i++) { exec.execute(new Runnable() { public void run() { if (!cacheManagerImpl.isContains(key)) { cacheManagerImpl.putCache(key, 1, 0); } else { //因为+1和赋值操作不是原子性的，所以把它用synchronize块包起来 synchronized (cacheManagerImpl) { int value = (Integer) cacheManagerImpl.getCacheDataByKey(key) + 1; cacheManagerImpl.putCache(key,value , 0); } } } }); } exec.shutdown(); try { exec.awaitTermination(1, TimeUnit.DAYS); } catch (InterruptedException e1) { e1.printStackTrace(); } logger.info(cacheManagerImpl.getCacheDataByKey(key).toString()); }}来源：http://www.jb51.net/article/111518.htm