Java 中常用快取Cache機制的實現

快取主要可分為二大類:

一、透過檔案快取,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、內存緩存，也就是實作一個類別中靜態Map,對這個Map進行常規的增刪查.

程式碼如下：

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 = 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();   
    
    }   
}