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 :

import java.util.*;

/**

* 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

//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

if (cacheDt <= 0||cacheDt>nowDt) {

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;

}

}

}

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();

}

}