所謂緩存，就是將程序或系統(tǒng)經(jīng)常要調(diào)用的對象存在內(nèi)存中，一遍其使用時可以快速調(diào)用，不必再去創(chuàng)建新的重復的實例。這樣做可以減少系統(tǒng)開銷，提高系統(tǒng)效率。

緩存主要可分為二大類:

一、通過文件緩存,顧名思義文件緩存是指把數(shù)據(jù)存儲在磁盤上，不管你是以XML格式，序列化文件DAT格式還是其它文件格式；

二、內(nèi)存緩存，也就是實現(xiàn)一個類中靜態(tài)Map,對這個Map進行常規(guī)的增刪查.

代碼如下 ：

package lhm.hcy.guge.frameset.cache; import java.util.*; //Description: 管理緩存 //可擴展的功能：當chche到內(nèi)存溢出時必須清除掉最早期的一些緩存對象，這就要求對每個緩存對象保存創(chuàng)建時間 public class CacheManager { private static HashMap cacheMap = new HashMap(); //單實例構(gòu)造方法 private CacheManager() { super(); } //獲取布爾值的緩存 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; } } //設置布爾值的緩存 public synchronized static boolean setSimpleFlag(String key,boolean flag){ if (flag &amp;&amp; getSimpleFlag(key)) {//假如為真不允許被覆蓋 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; } } //得到緩存。同步靜態(tài)方法 private synchronized static Cache getCache(String key) { return (Cache) cacheMap.get(key); } //判斷是否存在一個緩存 private synchronized static boolean hasCache(String key) { return cacheMap.containsKey(key); } //清除所有緩存 public synchronized static void clearAll() { cacheMap.clear(); } //清除某一類特定緩存,通過遍歷HASHMAP下的所有對象，來判斷它的KEY與傳入的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)) { //如果匹配則刪除掉 arr.add(key); } } for (int k = 0; k < arr.size(); k++) { clearOnly(arr.get(k)); } } catch (Exception ex) { ex.printStackTrace(); } } //清除指定的緩存 public synchronized static void clearOnly(String key) { cacheMap.remove(key); } //載入緩存 public synchronized static void putCache(String key, Cache obj) { cacheMap.put(key, obj); } //獲取緩存信息 public static Cache getCacheInfo(String key) { if (hasCache(key)) { Cache cache = getCache(key); if (cacheExpired(cache)) { //調(diào)用判斷是否終止方法 cache.setExpired(true); } return cache; }else return null; } //載入緩存信息 public static void putCacheInfo(String key, Cache obj, long dt,boolean expired) { Cache cache = new Cache(); cache.setKey(key); cache.setTimeOut(dt + System.currentTimeMillis()); //設置多久后更新緩存 cache.setValue(obj); cache.setExpired(expired); //緩存默認載入時，終止狀態(tài)為FALSE cacheMap.put(key, cache); } //重寫載入緩存信息方法 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); } //判斷緩存是否終止 public static boolean cacheExpired(Cache cache) { if (null == cache) { //傳入的緩存不存在 return false; } long nowDt = System.currentTimeMillis(); //系統(tǒng)當前的毫秒數(shù) long cacheDt = cache.getTimeOut(); //緩存內(nèi)的過期毫秒數(shù) if (cacheDt <= 0||cacheDt>nowDt) { //過期時間小于等于零時,或者過期時間大于當前時間時，則為FALSE return false; } else { //大于過期時間 即過期 return true; } } //獲取緩存中的大小 public static int getCacheSize() { return cacheMap.size(); } //獲取指定的類型的大小 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) { //如果匹配則刪除掉 k++; } } } catch (Exception ex) { ex.printStackTrace(); } return k; } //獲取緩存對象中的所有鍵值名稱 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; } } //獲取緩存對象中指定類型 的鍵值名稱 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;//緩存ID private Object value;//緩存數(shù)據(jù) private long timeOut;//更新時間 private boolean expired; //是否終止 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; } } //測試類， 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("刪除前的大?。?+CacheManager.getCacheSize()); //CacheManager.getCacheAllkey(); //CacheManager.clearAll("aaaa"); //System.out.println("刪除后的大小："+CacheManager.getCacheSize()); //CacheManager.getCacheAllkey(); } }