Java 中常用缓存Cache机制的实现

Cache所谓缓存，就是将程序或系统经常要调用的对象存在内存中，一遍其使用时可以快速调用，不必再去创建新的重复的实例。

这样做可以减少系统开销，提高系统效率。

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：package lhm.hcy.guge.frameset.cache;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;}elsereturn 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FALSEcacheMap.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FALSEreturn 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();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 {}}}package lhm.hcy.guge.frameset.cache;public class Cache {private String key;//缓存IDprivate 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 getV alue() {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();}}。