java 缓存的简单实现

import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; 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; } } }