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 ：
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 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();
}
}