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Java 中常用缓存Cache机制的实现

所谓缓存,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.
代码如下 :
package lhm.hcy.guge.frameset.cache;

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();

} 

}

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