JAVA缓存机制

缓存可分为二大类:
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.
下面为一个简单的缓存代码

Java代码

package lhm.hcy.guge.frameset.cache;

import java.util.*;

/**
 * Title:
 *
 * Description: 管理缓存
 * Deep blue 2008-11-28 think
 * 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
 * Copyright: Copyright (c) 2008
 *
 * Company:
 *
 * @author Deepblue  2008-11-11
 * @version 1.0
 */
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;

/**
 * Title:
 *
 * Description: 缓存DTO
 *
 * Copyright: Copyright (c) 2008
 *
 * Company:
 *
 * @author Deepblue  2008-11-11
 * @version 1.0
 */
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();


    }
}