Java中常用快取Cache機制的實現

所謂快取，就是將程式或系統經常要呼叫的物件存在記憶體中，一遍其使用時可以快速呼叫，不必再去建立新的重複的例項。這樣做可以減少系統開銷，提高系統效率。

快取主要可分為二大類:

一、通過檔案快取,顧名思義檔案快取是指把資料儲存在磁碟上，不管你是以XML格式，序列化檔案DAT格式還是其它檔案格式；

二、記憶體快取，也就是實現一個類中靜態Map,對這個Map進行常規的增刪查.

程式碼如下 ：

package lhm.hcy.guge.frameset.cache; 

import java.util.*; 

 //Description: 管理快取 

 //可擴充套件的功能：當chche到記憶體溢位時必須清除掉最早期的一些快取物件，這就要求對每個快取物件儲存建立時間 

public class CacheManager { 
    private static HashMap cacheMap = new HashMap(); 

    //單例項構造方法 
    private CacheManager() { 
        super(); 
    } 
    //獲取布林值的快取 
    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; 
        } 
    } 
    //設定布林值的快取 
    public synchronized static boolean setSimpleFlag(String key,boolean flag){ 
        if (flag && 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; 
        } 
    } 

    //得到快取。同步靜態方法 
    private synchronized static Cache getCache(String key) { 
        return (Cache) cacheMap.get(key); 
    } 

    //判斷是否存在一個快取 
    private synchronized static boolean hasCache(String key) { 
        return cacheMap.containsKey(key); 
    } 

    //清除所有快取 
    public synchronized static void clearAll() { 
        cacheMap.clear(); 
    } 

    //清除某一類特定快取,通過遍歷HASHMAP下的所有物件，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(); 
        } 
    } 

    //清除指定的快取 
    public synchronized static void clearOnly(String key) { 
        cacheMap.remove(key); 
    } 

    //載入快取 
    public synchronized static void putCache(String key, Cache obj) { 
        cacheMap.put(key, obj); 
    } 

    //獲取快取資訊 
    public static Cache getCacheInfo(String key) { 

        if (hasCache(key)) { 
            Cache cache = getCache(key); 
            if (cacheExpired(cache)) { //呼叫判斷是否終止方法 
                cache.setExpired(true); 
            } 
            return cache; 
        }else 
            return null; 
    } 

    //載入快取資訊 
    public static void putCacheInfo(String key, Cache obj, long dt,boolean expired) { 
        Cache cache = new Cache(); 
        cache.setKey(key); 
        cache.setTimeOut(dt + System.currentTimeMillis()); //設定多久後更新快取 
        cache.setValue(obj); 
        cache.setExpired(expired); //快取預設載入時，終止狀態為FALSE 
        cacheMap.put(key, cache); 
    } 
    //重寫載入快取資訊方法 
    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); 
    } 

    //判斷快取是否終止 
    public static boolean cacheExpired(Cache cache) { 
        if (null == cache) { //傳入的快取不存在 
            return false; 
        } 
        long nowDt = System.currentTimeMillis(); //系統當前的毫秒數 
        long cacheDt = cache.getTimeOut(); //快取內的過期毫秒數 
        if (cacheDt <= 0||cacheDt>nowDt) { //過期時間小於等於零時,或者過期時間大於當前時間時，則為FALSE 
            return false; 
        } else { //大於過期時間 即過期 
            return true; 
        } 
    } 

    //獲取快取中的大小 
    public static int getCacheSize() { 
        return cacheMap.size(); 
    } 

    //獲取指定的型別的大小 
    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; 
    } 

    //獲取快取物件中的所有鍵值名稱 
    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; 
        } 
    } 

    //獲取快取物件中指定型別 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;//快取ID 
        private Object value;//快取資料 
        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("刪除前的大小："+CacheManager.getCacheSize()); 
//        CacheManager.getCacheAllkey(); 
//        CacheManager.clearAll("aaaa"); 
//        System.out.println("刪除後的大小："+CacheManager.getCacheSize()); 
//        CacheManager.getCacheAllkey(); 

    } 
}