Java 中常用缓存Cache机制的实现详解编程语言

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.

代码如下 ：

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();    
    
    }    
}