java中实现简单cache

 

 

 

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
package org.netjframework.cache;

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;
}
}
}

cacheitem类：用于管理每个条目的cache内容和超时时间回调方法
package org.netjframework.cache;

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;
}
}

ICacheMethod接口：cache到期回调方法需要实现的接口
package org.netjframework.cache;

public interface ICacheMethod {

public void execute(String key);
}