JAVA缓存的实现

http://www.iteye.com/topic/544021

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 

Java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();


     }
 }