JAVA缓存的实现
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.*;???
??
/**??
?*?<p>Title:?</p>??
?*??
?*?<p>Description:?管理缓存</p>??
?*?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??
?*?<p>Copyright:?Copyright?(c)?2008</p>??
?*??
?*?<p>Company:?</p>??
?*??
?*?@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<String>?arr?=?new?ArrayList<String>();???
????????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<String>?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<String>?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;???
??
/**??
?*?<p>Title:?</p>??
?*??
?*?<p>Description:?缓存DTO</p>??
?*??
?*?<p>Copyright:?Copyright?(c)?2008</p>??
?*??
?*?<p>Company:?</p>??
?*??
?*?@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();???
??
??
????}???
}??
?
