Java中常用缓存Cache机制的实现 （转载）

缓存主要可分为二大类:

　　一、通过文件缓存,顾名思义文件缓存是指把数据存储在磁盘上，不管你是以XML格式，序列化文件DAT格式还是其它文件格式；

　　二、内存缓存，也就是实现一个类中静态Map,对这个Map进行常规的增删查.

　　代码如下 ：

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package lhm.hcy.guge.frameset.cache;   import java.util.*;    //Description: 管理缓存    //可扩展的功能：当chche到内存溢出时必须清除掉最早期的一些缓存对象，这就要求对每个缓存对象保存创建时间   public class CacheManager {     private static HashMap cacheMap = new HashMap();       //单实例构造方法     private CacheManager() {         super();     }     //获取布尔值的缓存     public static boolean getSimpleFlag(String key){         try{             return (Boolean) cacheMap.get(key);         }catch(NullPointerException e){             return false;         }     }     public static long getServerStartdt(String key){         try {             return (Long)cacheMap.get(key);         } catch (Exception ex) {             return 0;         }     }     //设置布尔值的缓存     public synchronized static boolean setSimpleFlag(String key,boolean flag){         if (flag &amp;&amp; getSimpleFlag(key)) {//假如为真不允许被覆盖             return false;         }else{             cacheMap.put(key, flag);             return true;         }     }     public synchronized static boolean setSimpleFlag(String key,long serverbegrundt){         if (cacheMap.get(key) == null) {             cacheMap.put(key,serverbegrundt);             return true;         }else{             return false;         }     }       //得到缓存。同步静态方法     private synchronized static Cache getCache(String key) {         return (Cache) cacheMap.get(key);     }       //判断是否存在一个缓存     private synchronized static boolean hasCache(String key) {         return cacheMap.containsKey(key);     }       //清除所有缓存     public synchronized static void clearAll() {         cacheMap.clear();     }       //清除某一类特定缓存,通过遍历HASHMAP下的所有对象，来判断它的KEY与传入的TYPE是否匹配     public synchronized static void clearAll(String type) {         Iterator i = cacheMap.entrySet().iterator();         String key;         ArrayList arr = new ArrayList();         try {             while (i.hasNext()) {                 java.util.Map.Entry entry = (java.util.Map.Entry) i.next();                 key = (String) entry.getKey();                 if (key.startsWith(type)) { //如果匹配则删除掉                     arr.add(key);                 }             }             for (int k = 0; k < arr.size(); k++) {                 clearOnly(arr.get(k));             }         } catch (Exception ex) {             ex.printStackTrace();         }     }       //清除指定的缓存     public synchronized static void clearOnly(String key) {         cacheMap.remove(key);     }       //载入缓存     public synchronized static void putCache(String key, Cache obj) {         cacheMap.put(key, obj);     }       //获取缓存信息     public static Cache getCacheInfo(String key) {           if (hasCache(key)) {             Cache cache = getCache(key);             if (cacheExpired(cache)) { //调用判断是否终止方法                 cache.setExpired(true);             }             return cache;         }else             return null;     }       //载入缓存信息     public static void putCacheInfo(String key, Cache obj, long dt,boolean expired) {         Cache cache = new Cache();         cache.setKey(key);         cache.setTimeOut(dt + System.currentTimeMillis()); //设置多久后更新缓存         cache.setValue(obj);         cache.setExpired(expired); //缓存默认载入时，终止状态为FALSE         cacheMap.put(key, cache);     }     //重写载入缓存信息方法     public static void putCacheInfo(String key,Cache obj,long dt){         Cache cache = new Cache();         cache.setKey(key);         cache.setTimeOut(dt+System.currentTimeMillis());         cache.setValue(obj);         cache.setExpired(false);         cacheMap.put(key,cache);     }       //判断缓存是否终止     public static boolean cacheExpired(Cache cache) {         if (null == cache) { //传入的缓存不存在             return false;         }         long nowDt = System.currentTimeMillis(); //系统当前的毫秒数         long cacheDt = cache.getTimeOut(); //缓存内的过期毫秒数         if (cacheDt <= 0||cacheDt>nowDt) { //过期时间小于等于零时,或者过期时间大于当前时间时，则为FALSE             return false;         } else { //大于过期时间 即过期             return true;         }     }       //获取缓存中的大小     public static int getCacheSize() {         return cacheMap.size();     }       //获取指定的类型的大小     public static int getCacheSize(String type) {         int k = 0;         Iterator i = cacheMap.entrySet().iterator();         String key;         try {             while (i.hasNext()) {                 java.util.Map.Entry entry = (java.util.Map.Entry) i.next();                 key = (String) entry.getKey();                 if (key.indexOf(type) != -1) { //如果匹配则删除掉                     k++;                 }             }         } catch (Exception ex) {             ex.printStackTrace();         }           return k;     }       //获取缓存对象中的所有键值名称     public static ArrayList getCacheAllkey() {         ArrayList a = new ArrayList();         try {             Iterator i = cacheMap.entrySet().iterator();             while (i.hasNext()) {                 java.util.Map.Entry entry = (java.util.Map.Entry) i.next();                 a.add((String) entry.getKey());             }         } catch (Exception ex) {} finally {             return a;         }     }       //获取缓存对象中指定类型 的键值名称     public static ArrayList getCacheListkey(String type) {         ArrayList a = new ArrayList();         String key;         try {             Iterator i = cacheMap.entrySet().iterator();             while (i.hasNext()) {                 java.util.Map.Entry entry = (java.util.Map.Entry) i.next();                 key = (String) entry.getKey();                 if (key.indexOf(type) != -1) {                     a.add(key);                 }             }         } catch (Exception ex) {} finally {             return a;         }     }   }   package lhm.hcy.guge.frameset.cache;   public class Cache {         private String key;//缓存ID         private Object value;//缓存数据         private long timeOut;//更新时间         private boolean expired; //是否终止         public Cache() {                 super();         }           public Cache(String key, Object 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;         } }   //测试类， class Test {     public static void main(String[] args) {         System.out.println(CacheManager.getSimpleFlag("alksd")); //        CacheManager.putCache("abc", new Cache()); //        CacheManager.putCache("def", new Cache()); //        CacheManager.putCache("ccc", new Cache()); //        CacheManager.clearOnly(""); //        Cache c = new Cache(); //        for (int i = 0; i < 10; i++) { //            CacheManager.putCache("" + i, c); //        } //        CacheManager.putCache("aaaaaaaa", c); //        CacheManager.putCache("abchcy;alskd", c); //        CacheManager.putCache("cccccccc", c); //        CacheManager.putCache("abcoqiwhcy", c); //        System.out.println("删除前的大小："+CacheManager.getCacheSize()); //        CacheManager.getCacheAllkey(); //        CacheManager.clearAll("aaaa"); //        System.out.println("删除后的大小："+CacheManager.getCacheSize()); //        CacheManager.getCacheAllkey();       } }