java缓存技术学习

package com.citics.crm.customerwidget.utils;  
  
/** 
 * <p>Description: 缓存DTO</p> 
 * @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;  
        }  
}  
  



package com.citics.crm.customerwidget.utils;  
  
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 
 * @version 1.0 
 */  
public class CacheUtil {  
    private static HashMap cacheMap = new HashMap();  
  
    //单实例构造方法  
    private CacheUtil() {  
        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;  
        }  
    }  
  
}  
  
  

 

 

评论

4 楼 SpringJava 2014-07-29  

freezingsky 写道

SpringJava 写道

//private static HashMap cacheMap = new HashMap();

//改为：
private static ConcurrentHashMap<K, V> cacheMap = new ConcurrentHashMap<K, V>();

还不止这个，不信你多线程跑跑试试。

是的，在有put,remove操作之处加ReentrantReadWriteLock。

3 楼 freezingsky 2014-07-26  

SpringJava 写道

//private static HashMap cacheMap = new HashMap();

//改为：
private static ConcurrentHashMap<K, V> cacheMap = new ConcurrentHashMap<K, V>();

还不止这个，不信你多线程跑跑试试。

2 楼 SpringJava 2014-07-26  

//private static HashMap cacheMap = new HashMap();

//改为：
private static ConcurrentHashMap<K, V> cacheMap = new ConcurrentHashMap<K, V>();

1 楼 freezingsky 2014-07-26  

缺少考虑并发情况！