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Java中常用缓存Cache机制的实现

    缓存,就是将程序或系统经常要调用的对象存在内存中,一遍其使用时可以快速调用,不必再去创建新的重复的实例。这样做可以减少系统开销,提高系统效率。

    缓存主要可分为二大类:
    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. 

import java.util.*; 

 //Description: 管理缓存 

 //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 

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; 

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 = http://www.mamicode.com/value; "hljs-keyword">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 = http://www.mamicode.com/object; "hljs-keyword">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(); 


    } 
} 
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    Java中常用缓存Cache机制的实现