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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
- package lhm.hcy.guge.frameset.cache;
- import java.util.*;
- /**
- * <p>Title: </p>
- *
- * <p>Description: 管理缓存</p>
- * Deep blue 2008-11-28 think
- * 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
- * <p>Copyright: Copyright (c) 2008</p>
- *
- * <p>Company: </p>
- *
- * @author Deepblue 2008-11-11
- * @version 1.0
- */
- 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<String> arr = new ArrayList<String>();
- 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 <= 0||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<String> 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<String> 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;
- /**
- * <p>Title: </p>
- *
- * <p>Description: 缓存DTO</p>
- *
- * <p>Copyright: Copyright (c) 2008</p>
- *
- * <p>Company: </p>
- *
- * @author Deepblue 2008-11-11
- * @version 1.0
- */
- 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();
- }
- }
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