转载自  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;}elsereturn 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FALSEcacheMap.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FALSEreturn 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IDprivate 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();}
}