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缓存可分为二大类: 
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. 
下面为一个简单的缓存代码 

package lhm.hcy.guge.frameset.cache;import java.util.*;/** * 
Title: 
 * * 
Description: 管理缓存
 * Deep blue 2008-11-28 think * 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 * 
Copyright: Copyright (c) 2008
 * * 
Company: 
 * * @author Deepblue  2008-11-11 * @version 1.0 */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 && 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;/** * 
       
Title: 
 * * 
       
Description: 缓存DTO
 * * 
       
Copyright: Copyright (c) 2008
 * * 
       
Company: 
 * * @author Deepblue  2008-11-11 * @version 1.0 */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();    }}
      
     
    
   

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