java cache过期策略两种实现，一个基于list轮询一个基于timer定时

最近项目要引入缓存机制，但是不想引入分布式的缓存框架，所以自己就写了一个轻量级的缓存实现，有两个版本，一个是通过timer实现其超时过期处理，另外一个是通过list轮询。
首先要了解下java1.6中的ConcurrentMap ，他是一个线程安全的Map实现，特别说明的是在没有特别需求的情况下可以用ConcurrentHashMap。我是想学习一下读写锁的应用，就自己实现了一个SimpleConcurrentHashMap.

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package com.cttc.cache.entity;
import java.util.ArrayList;
import java.util.Collection;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
public class SimpleConcurrentMap<K, V> implements Map<K, V> {
final ReadWriteLock lock = new ReentrantReadWriteLock();
final Lock r = lock.readLock();
final Lock w = lock.writeLock();
final Map<K, V> map;
public SimpleConcurrentMap(Map<K, V> map) {
this.map = map;
if (map == null) throw new NullPointerException();
}
public void clear() {
w.lock();
try {
map.clear();
} finally {
w.unlock();
}
}
public boolean containsKey(Object key) {
r.lock();
try {
return map.containsKey(key);
} finally {
r.unlock();
}
}
public boolean containsValue(Object value) {
r.lock();
try {
return map.containsValue(value);
} finally {
r.unlock();
}
}
public Set<java.util.Map.Entry<K, V>> entrySet() {
throw new UnsupportedOperationException();
}
public V get(Object key) {
r.lock();
try {
return map.get(key);
} finally {
r.unlock();
}
}
public boolean isEmpty() {
r.lock();
try {
return map.isEmpty();
} finally {
r.unlock();
}
}
public Set<K> keySet() {
r.lock();
try {
return new HashSet<K>(map.keySet());
} finally {
r.unlock();
}
}
public V put(K key, V value) {
w.lock();
try {
return map.put(key, value);
} finally {
w.unlock();
}
}
public void putAll(Map<? extends K, ? extends V> m) {
w.lock();
try {
map.putAll(m);
} finally {
w.unlock();
}
}
public V remove(Object key) {
w.lock();
try {
return map.remove(key);
} finally {
w.unlock();
}
}
public int size() {
r.lock();
try {
return map.size();
} finally {
r.unlock();
}
}
public Collection<V> values() {
r.lock();
try {
return new ArrayList<V>(map.values());
} finally {
r.unlock();
}
}
}

缓存对象CacheEntity.Java为：

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package com.cttc.cache.entity;
import java.io.Serializable;
public class CacheEntity implements Serializable{
private static final long serialVersionUID = -3971709196436977492L;
private final int DEFUALT_VALIDITY_TIME = 20;//默认过期时间 20秒
private String cacheKey;
private Object cacheContext;
private int validityTime;//有效期时长，单位：秒
private long timeoutStamp;//过期时间戳
private CacheEntity(){
this.timeoutStamp = System.currentTimeMillis() + DEFUALT_VALIDITY_TIME * 1000;
this.validityTime = DEFUALT_VALIDITY_TIME;
}
public CacheEntity(String cacheKey, Object cacheContext){
this();
this.cacheKey = cacheKey;
this.cacheContext = cacheContext;
}
public CacheEntity(String cacheKey, Object cacheContext, long timeoutStamp){
this(cacheKey, cacheContext);
this.timeoutStamp = timeoutStamp;
}
public CacheEntity(String cacheKey, Object cacheContext, int validityTime){
this(cacheKey, cacheContext);
this.validityTime = validityTime;
this.timeoutStamp = System.currentTimeMillis() + validityTime * 1000;
}
public String getCacheKey() {
return cacheKey;
}
public void setCacheKey(String cacheKey) {
this.cacheKey = cacheKey;
}
public Object getCacheContext() {
return cacheContext;
}
public void setCacheContext(Object cacheContext) {
this.cacheContext = cacheContext;
}
public long getTimeoutStamp() {
return timeoutStamp;
}
public void setTimeoutStamp(long timeoutStamp) {
this.timeoutStamp = timeoutStamp;
}
public int getValidityTime() {
return validityTime;
}
public void setValidityTime(int validityTime) {
this.validityTime = validityTime;
}
}

List缓存处理对象：

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package com.cttc.cache.handler;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import com.cttc.cache.entity.CacheEntity;
import com.cttc.cache.entity.SimpleConcurrentMap;
/**
* @projName：WZServer
* @className：CacheHandler
* @description：缓存操作类，对缓存进行管理，采用处理队列，定时循环清理的方式
* @creater：Administrator
* @creatTime：2013年7月22日上午9:18:54
* @alter：Administrator
* @alterTime：2013年7月22日上午9:18:54
* @remark：
* @version
*/
public class CacheListHandler {
private static final long SECOND_TIME = 1000;
private static final SimpleConcurrentMap<String, CacheEntity> map;
private static final List<CacheEntity> tempList;
static{
tempList = new ArrayList<CacheEntity>();
map = new SimpleConcurrentMap<String, CacheEntity>(new HashMap<String, CacheEntity>(1<<18));
new Thread(new TimeoutTimerThread()).start();
}
/**
* 增加缓存对象
* @param key
* @param ce
*/
public static void addCache(String key, CacheEntity ce){
addCache(key, ce, ce.getValidityTime());
}
/**
* 增加缓存对象
* @param key
* @param ce
* @param validityTime 有效时间
*/
public static synchronized void addCache(String key, CacheEntity ce, int validityTime){
ce.setTimeoutStamp(System.currentTimeMillis() + validityTime * SECOND_TIME);
map.put(key, ce);
//添加到过期处理队列
tempList.add(ce);
}
/**
* 获取缓存对象
* @param key
* @return
*/
public static synchronized CacheEntity getCache(String key){
return map.get(key);
}
/**
* 检查是否含有制定key的缓冲
* @param key
* @return
*/
public static synchronized boolean isConcurrent(String key){
return map.containsKey(key);
}
/**
* 删除缓存
* @param key
*/
public static synchronized void removeCache(String key){
map.remove(key);
}
/**
* 获取缓存大小
* @param key
*/
public static int getCacheSize(){
return map.size();
}
/**
* 清除全部缓存
*/
public static synchronized void clearCache(){
tempList.clear();
map.clear();
System.out.println("clear cache");
}
static class TimeoutTimerThread implements Runnable {
public void run(){
while(true){
try {
checkTime();
} catch (Exception e) {
e.printStackTrace();
}
}
}
/**
* 过期缓存的具体处理方法
* @throws Exception
*/
private void checkTime() throws Exception{
//"开始处理过期 ";
CacheEntity tce = null;
long timoutTime = 1000L;
//" 过期队列大小 : "+tempList.size());
if(1 > tempList.size()){
System.out.println("过期队列空，开始轮询");
timoutTime = 1000L;
Thread.sleep(timoutTime);
return;
}
tce = tempList.get(0);
timoutTime = tce.getTimeoutStamp() - System.currentTimeMillis();
//" 过期时间 : "+timoutTime);
if(0 < timoutTime){
//设定过期时间
Thread.sleep(timoutTime);
return;
}
System.out.print(" 清除过期缓存： "+tce.getCacheKey());
//清除过期缓存和删除对应的缓存队列
tempList.remove(tce);
removeCache(tce.getCacheKey());
}
}
}

Timer方式

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package com.cttc.cache.handler;
import java.util.HashMap;
import java.util.Timer;
import java.util.TimerTask;
import com.cttc.cache.entity.CacheEntity;
import com.cttc.cache.entity.SimpleConcurrentMap;
/**
* @projName：WZServer
* @className：CacheHandler
* @description：缓存操作类，对缓存进行管理,清除方式采用Timer定时的方式
* @creater：Administrator
* @creatTime：2013年7月22日上午9:18:54
* @alter：Administrator
* @alterTime：2013年7月22日上午9:18:54
* @remark：
* @version
*/
public class CacheTimerHandler {
private static final long SECOND_TIME = 1000;//默认过期时间 20秒
private static final int DEFUALT_VALIDITY_TIME = 20;//默认过期时间 20秒
private static final Timer timer ;
private static final SimpleConcurrentMap<String, CacheEntity> map;
static{
timer = new Timer();
map = new SimpleConcurrentMap<String, CacheEntity>(new HashMap<String, CacheEntity>(1<<18));
}
/**
* 增加缓存对象
* @param key
* @param ce
*/
public static void addCache(String key, CacheEntity ce){
addCache(key, ce, DEFUALT_VALIDITY_TIME);
}
/**
* 增加缓存对象
* @param key
* @param ce
* @param validityTime 有效时间
*/
public static synchronized void addCache(String key, CacheEntity ce, int validityTime){
map.put(key, ce);
//添加过期定时
timer.schedule(new TimeoutTimerTask(key), validityTime * SECOND_TIME);
}
/**
* 获取缓存对象
* @param key
* @return
*/
public static synchronized CacheEntity getCache(String key){
return map.get(key);
}
/**
* 检查是否含有制定key的缓冲
* @param key
* @return
*/
public static synchronized boolean isConcurrent(String key){
return map.containsKey(key);
}
/**
* 删除缓存
* @param key
*/
public static synchronized void removeCache(String key){
map.remove(key);
}
/**
* 获取缓存大小
* @param key
*/
public static int getCacheSize(){
return map.size();
}
/**
* 清除全部缓存
*/
public static synchronized void clearCache(){
if(null != timer){
timer.cancel();
}
map.clear();
System.out.println("clear cache");
}
/**
* @projName：WZServer
* @className：TimeoutTimerTask
* @description：清除超时缓存定时服务类
* @creater：Administrator
* @creatTime：2013年7月22日上午9:34:39
* @alter：Administrator
* @alterTime：2013年7月22日上午9:34:39
* @remark：
* @version
*/
static class TimeoutTimerTask extends TimerTask{
private String ceKey ;
public TimeoutTimerTask(String key){
this.ceKey = key;
}
@Override
public void run() {
CacheTimerHandler.removeCache(ceKey);
System.out.println("remove : "+ceKey);
}
}
}

timer方式有点是适用性更强，因为每个缓存的过期时间都可以独立配置的；ist只能适用于缓存时间都一样的线性过期。从性能开销方面，因为timer是与缓存对象数量成正比的，在缓存量很大的时候，在缓存时间内系统开销也随之提高；而list方式只要一个线程管理过期清理就可以了。

这里要感谢饭饭泛，从其微博学习到很多http://www.blogjava.net/xylz/archive/2010/07/14/326080.html

对timer方式的改进，定时程序只需要一个就可以了，过期时间，通过一个对象保存，根据每个对象的过期时间判断是否移除该缓存。于是得到下面的版本：

package com.cttc.cache.handler;

import java.util.HashMap;
import java.util.Map;
import java.util.Timer;
import java.util.TimerTask;
/**
 * 在缓存的时候，同时记录下该key,缓存时间，失效周期
 * 在读取缓存的时候，更新该key的缓存时间，
 * 定时器每两个小时运行一次，检查每个key是否过期，如果过期，删除Jboss中的cache
 *
 */
public class CacheTimerMamager{
private static final long SECOND_TIME = 1000;//毫秒
private static final long DEFUALT_VALIDITY_TIME = SECOND_TIME * 60 * 60 * 2;//默认过期时间 :2小时
private static final Timer timer ;
private static final Map<String, CacheOutTime> map;

static{
timer = new Timer();
map = new HashMap<String, CacheOutTime>();
timer.schedule(new CacheTimerTask(), DEFUALT_VALIDITY_TIME, DEFUALT_VALIDITY_TIME);
}

/**
 * 增加缓存对象
 * @param key
 * @param ce
 */
public static synchronized void  addCache(String key){
CacheOutTime cot = map.get(key);
long outTime = System.currentTimeMillis()+DEFUALT_VALIDITY_TIME;
if(cot==null){
cot = new CacheOutTime(key, outTime);
map.put(key, cot);
}else{
//更新该key的过期时间
cot.setTimeoutStamp(outTime);
}
}

//移除cache
/**
 * 考虑，在多线程时，当有线程已经取得缓存对象时，删掉了缓存，会产生什么情况
 */
public static synchronized void removeCache() {
CacheOutTime cot;
long currentTime = System.currentTimeMillis();
for (String key : map.keySet()) {
cot = map.get(key);
if(cot.getTimeoutStamp()<=currentTime){
System.out.println("remove : "+key);
}
}
}
static class CacheTimerTask extends TimerTask{
@Override
public void run() {
//移除cache
CacheTimerMamager.removeCache();
}
}

}

class CacheOutTime {
private String cacheKey;
private long timeoutStamp;//过期时间戳，在最后一次访问该key的时候计算得到

public CacheOutTime() {
super();
}
public CacheOutTime(String cacheKey, long timeoutStamp) {
super();
this.cacheKey = cacheKey;
this.timeoutStamp = timeoutStamp;
}

public String getCacheKey() {
return cacheKey;
}
public void setCacheKey(String cacheKey) {
this.cacheKey = cacheKey;
}
public long getTimeoutStamp() {
return timeoutStamp;
}
public void setTimeoutStamp(long timeoutStamp) {
this.timeoutStamp = timeoutStamp;
}
}

package com.cttc.cache.handler;
import java.util.HashMap;import java.util.Map;import java.util.Timer;import java.util.TimerTask;/** * 在缓存的时候，同时记录下该key,缓存时间，失效周期 * 在读取缓存的时候，更新该key的缓存时间， * 定时器每两个小时运行一次，检查每个key是否过期，如果过期，删除Jboss中的cache * */public class CacheTimerMamager{private static final long SECOND_TIME = 1000;//毫秒private static final long DEFUALT_VALIDITY_TIME = SECOND_TIME * 60 * 60 * 2;//默认过期时间 :2小时private static final Timer timer ;private static final Map<String, CacheOutTime> map;static{timer = new Timer();map = new HashMap<String, CacheOutTime>();timer.schedule(new CacheTimerTask(), DEFUALT_VALIDITY_TIME, DEFUALT_VALIDITY_TIME);}/** * 增加缓存对象 * @param key * @param ce */public static synchronized void addCache(String key){CacheOutTime cot = map.get(key);long outTime = System.currentTimeMillis()+DEFUALT_VALIDITY_TIME;if(cot==null){cot = new CacheOutTime(key, outTime);map.put(key, cot);}else{//更新该key的过期时间cot.setTimeoutStamp(outTime);}}//移除cache/** * 考虑，在多线程时，当有线程已经取得缓存对象时，删掉了缓存，会产生什么情况 */public static synchronized void removeCache() {CacheOutTime cot;long currentTime = System.currentTimeMillis();for (String key : map.keySet()) {cot = map.get(key);if(cot.getTimeoutStamp()<=currentTime){System.out.println("remove : "+key);}}}static class CacheTimerTask extends TimerTask{@Overridepublic void run() {//移除cacheCacheTimerMamager.removeCache();}}}
class CacheOutTime {private String cacheKey;private long timeoutStamp;//过期时间戳，在最后一次访问该key的时候计算得到public CacheOutTime() {super();}public CacheOutTime(String cacheKey, long timeoutStamp) {super();this.cacheKey = cacheKey;this.timeoutStamp = timeoutStamp;}public String getCacheKey() {return cacheKey;}public void setCacheKey(String cacheKey) {this.cacheKey = cacheKey;}public long getTimeoutStamp() {return timeoutStamp;}public void setTimeoutStamp(long timeoutStamp) {this.timeoutStamp = timeoutStamp;}}

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java cache过期策略两种实现，一个基于list轮询一个基于timer定时

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