自己动手实现java中cache

实现思路： 
创建一个静态Hashtable用于保存key和value,对于cache过期后的方法回调，在cache过期后，再访问cache的时候进行，避免了使用定时器轮询过期时间，进行cache清除的效率损耗。 
使用synchronized关键字进行多线程同步。 
包括二个类和一个接口： 
cache类：里面都是静态方法,提供基于key,value的方法进行cache的添加，修改，访问,进行cache过期后调用callback方法。 

cacheitem类：用于管理每个条目的cache内容和超时时间回调方法 

ICacheMethod接口：cache到期回调方法需要实现的接口 

cache类：里面都是静态方法 

import java.util.Date;

public class Cache {

	private static java.util.Hashtable<String, Object> __cacheList = new java.util.Hashtable<String, Object>();

	public Cache() {

	}

	// 添加cache,不过期
	public synchronized static void add(String key, Object value) {
		Cache.add(key, value, -1);
	}

	// 添加cache有过期时间
	public synchronized static void add(String key, Object value, long timeOut) {
		Cache.add(key, value, timeOut, null);
	}

	// 添加cache有过期时间并且具有回调方法
	public synchronized static void add(String key, Object value, long timeOut, ICacheMethod callback) {
		if (timeOut > 0) {
			timeOut += new Date().getTime();
		}
		CacheItem item = new CacheItem(key, value, timeOut, callback);
		Cache.__cacheList.put(key, item);
	}

	// 获取cache
	public synchronized static Object get(String key) {
		Object obj = Cache.__cacheList.get(key);
		if (obj == null) {
			return null;
		}
		CacheItem item = (CacheItem) obj;
		boolean expired = Cache.cacheExpired(key);
		if (expired == true) // 已过期
		{
			if (item.getCallback() == null) {
				Cache.remove(key);
				return null;
			} else {
				ICacheMethod callback = item.getCallback();
				callback.execute(key);
				expired = Cache.cacheExpired(key);
				if (expired == true) {
					Cache.remove(key);
					return null;
				}
			}
		}
		return item.getValue();
	}

	// 移除cache
	public synchronized static void remove(String key) {
		Object obj = Cache.__cacheList.get(key);
		if (obj != null) {
			obj = null;
		}
		Cache.__cacheList.remove(key);
	}

	// 清理所有cache对象
	public synchronized static void clear() {

		for (String s : Cache.__cacheList.keySet()) {
			Cache.__cacheList.put(s, null);
		}
		Cache.__cacheList.clear();
	}

	// 判断是否过期
	private static boolean cacheExpired(String key) {
		CacheItem item = (CacheItem) Cache.__cacheList.get(key);
		if (item == null) {
			return false;
		}
		long milisNow = new Date().getTime();
		long milisExpire = item.getTimeOut();
		if (milisExpire <= 0) { // 不过期
			return false;
		} else if (milisNow >= milisExpire) {
			return true;
		} else {
			return false;
		}
	}
}

　　

public class CacheItem {

	private String key;
	private Object value;
	private long timeOut;
	private ICacheMethod callback = null;

	public CacheItem() {

	}

	public ICacheMethod getCallback() {
		return callback;
	}

	public void setCallback(ICacheMethod callback) {
		this.callback = callback;
	}

	public CacheItem(String key, Object value) {
		this.key = key;
		this.value = value;
		this.timeOut = 0;
	}

	public CacheItem(String key, Object value, long timeOut) {
		this.key = key;
		this.value = value;
		this.timeOut = timeOut;
	}

	public CacheItem(String key, Object value, long timeOut, ICacheMethod callback) {
		this.key = key;
		this.value = value;
		this.timeOut = timeOut;
		this.callback = callback;
	}

	public String getKey() {
		return key;
	}

	public void setKey(String key) {
		this.key = key;
	}

	public Object getValue() {
		return value;
	}

	public void setValue(Object value) {
		this.value = value;
	}

	public long getTimeOut() {
		return timeOut;
	}

	public void setTimeOut(long timeOut) {
		this.timeOut = timeOut;
	}
}

　　

public interface ICacheMethod {
	public void execute(String key); 
}