java缓存

 图片如有雷同,那一定是缘分

概念:

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，以便再次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.

class一:

package com.yin.cache;

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


/**
 * @Explain 
 * @author  yinyl
 * @version 2017-3-9 上午9:33:59
 * 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((String) 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 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; 
            } 
        } 

}

class二:

package com.yin.cache;

/**
 *
 * @Explain 
 * @author  yinyl
 * @version 2017-3-9 上午9:34:40
 *
 */
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; 
      } 
}

class三:

package com.yin.cache;

/**
 *
 * @Explain 
 * @author  yinyl
 * @version 2017-3-9 上午9:35:06
 *
 */
public class TestCache
{

    /**
     * @param args
     */
    public static void main(String[] args)
    {
         System.out.println(CacheManager.getSimpleFlag("yinyanling is a beautiful girl")); 
       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(); 


    }

}