用JAVA实现缓存

     在 开发 项目工程时，经常会遇到保存某些值放 到系统的 cache 中，现用 Cache.java 和 CacheManager.java 来管理。具体 代码 分别如下：

public class Cache { 
        private String key; 
        private Object value; 
        private long timeOut; 
        private boolean expired;

        public Cache() {
                super();
        }
                
        public Cache(String key, String value, long timeOut, boolean expired) {
                this.key = key;
                this.value = value;
                this.timeOut = timeOut;
                this.expired = expired;
        }

        public String getKey() {
                return key;
        }

        public long getTimeOut() {
                return timeOut;
        }

        public Object getValue() {
                return value;
        }

        public void setKey(String string) {
                key = string;
        }

        public void setTimeOut(long l) {
                timeOut = l;
        }

        public void setValue(Object object) {
                value = object;
        }

        public boolean isExpired() {
                return expired;
        }

        public void setExpired(boolean b) {
                expired = b;
        }
}

另 外一个类： 
import   java .util.Date;
import java.util.HashMap;

public class CacheManager {
        private static HashMap cacheMap = new HashMap();

        /**
         * This class is singleton so private constructor is used.
         */
        private CacheManager() {
                super();
        }

        /**
         * returns cache item from hashmap
         * @param key
         * @return Cache
         */
        private synchronized static Cache getCache(String key) {
                return (Cache)cacheMap.get(key);
        }

        /**
         * Looks at   the   hashmap if a cache item exists or   not 
         * @param key
         * @return Cache
         */
        private synchronized static boolean hasCache(String key) {
                return cacheMap.containsKey(key);
        }

        /**
         * Invalidates all cache
         */
        public synchronized static void invalidateAll() {
                cacheMap.clear();
        }

        /**
         * Invalidates a single cache item
         * @param key
         */
        public synchronized static void invalidate(String key) {
                cacheMap.remove(key);
        }

        /**
         * Adds new item to cache hashmap
         * @param key
         * @return Cache
         */
        private synchronized static void putCache(String key, Cache object) {
           cacheMap.put(key, object);
        }

        /**
         * Reads a cache item's content
         * @param key
         * @return
         */
        public static Cache getContent(String key) {
                 if (hasCache(key)) {
                        Cache cache = getCache(key);
                        if (cacheExpired(cache)) {
                                cache.setExpired(true);
                        }
                        return cache;
                 } else {
                         return null;
                 }
        }

        /**
         * 
         * @param key
         * @param content
         * @param ttl
         */
        public static void putContent(String key, Object content, long ttl) {
                Cache cache = new Cache();
                cache.setKey(key);
                cache.setValue(content);
                cache.setTimeOut(ttl + new Date().getTime());
                cache.setExpired(false);
                putCache(key, cache);
        }
        
        /** @modelguid {172828D6-3AB2-46C4-96E2-E72B34264031} */
        private static boolean cacheExpired(Cache cache) {
                if (cache == null) {
                        return false;
                }
                long milisNow = new Date().getTime();
                long milisExpire = cache.getTimeOut();
                if (milisExpire < 0) {                // Cache never expires 
                        return false;
                } else if (milisNow >= milisExpire) {
                        return true;
                } else {
                        return false;
                }
        }

}