Java 中常用緩存Cache機制的實現

核心就是 一個 static hashMap

Cache.java

package memcahe;

public class Cache {
    private String key;//緩存ID
    private Object value;//緩存數據
    private long timeOut;//更新時間
    private boolean expired; //是否終止
    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;
    }
}

CacheManager.java

package memcahe;
import java.util.*;

//Description: 管理緩存

//可擴展的功能：當chche到內存溢出時必須清除掉最早期的一些緩存對象，這就要求對每個緩存對象保存創建時間

public class CacheManager {
    private static HashMap cacheMap = new HashMap();

    //單實例構造方法
    private CacheManager() {
        super();
    }
    //獲取布爾值的緩存
    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;
        }
    }
    //設置布爾值的緩存
    public synchronized static boolean setSimpleFlag(String key,boolean flag){
        if (flag &&getSimpleFlag(key)) {//假如爲真不允許被覆蓋
            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;
        }
    }


    //得到緩存。同步靜態方法
    private synchronized static Cache getCache(String key) {
        return (Cache) cacheMap.get(key);
    }

    //判斷是否存在一個緩存
    private synchronized static boolean hasCache(String key) {
        return cacheMap.containsKey(key);
    }

    //清除所有緩存
    public synchronized static void clearAll() {
        cacheMap.clear();
    }

    //清除某一類特定緩存,通過遍歷HASHMAP下的所有對象，來判斷它的KEY與傳入的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)) { //如果匹配則刪除掉
                    arr.add(key);
                }
            }
            for (int k = 0; k <arr.size(); k++) {
                clearOnly((String)arr.get(k));
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    //清除指定的緩存
    public synchronized static void clearOnly(String key) {
        cacheMap.remove(key);
    }

    //載入緩存
    public synchronized static void putCache(String key, Cache obj) {
        cacheMap.put(key, obj);
    }

    //獲取緩存信息
    public static Cache getCacheInfo(String key) {

        if (hasCache(key)) {
            Cache cache = getCache(key);
            if (cacheExpired(cache)) { //調用判斷是否終止方法
                cache.setExpired(true);
            }
            return cache;
        }else
            return null;
    }

    //載入緩存信息
    public static void putCacheInfo(String key, Cache obj, long dt,boolean expired) {
        Cache cache = new Cache();
        cache.setKey(key);
        cache.setTimeOut(dt + System.currentTimeMillis()); //設置多久後更新緩存
        cache.setValue(obj);
        cache.setExpired(expired); //緩存默認載入時，終止狀態爲FALSE
        cacheMap.put(key, cache);
    }
    //重寫載入緩存信息方法
    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);
    }

    //判斷緩存是否終止
    public static boolean cacheExpired(Cache cache) {
        if (null == cache) { //傳入的緩存不存在
            return false;
        }
        long nowDt = System.currentTimeMillis(); //系統當前的毫秒數
        long cacheDt = cache.getTimeOut(); //緩存內的過期毫秒數
        if (cacheDt <= 0||cacheDt>nowDt) { //過期時間小於等於零時,或者過期時間大於當前時間時，則爲FALSE
            return false;
        } else { //大於過期時間 即過期
            return true;
        }
    }

    //獲取緩存中的大小
    public static int getCacheSize() {
        return cacheMap.size();
    }

    //獲取指定的類型的大小
    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) { //如果匹配則刪除掉
                    k++;
                }
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }

        return k;
    }

    //獲取緩存對象中的所有鍵值名稱
    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;
        }
    }

    //獲取緩存對象中指定類型 的鍵值名稱
    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;
        }
    }

}

test.java

package memcahe;

import java.util.ArrayList;

/**
 * Created by Administrator on 2017/3/1.
 */
//測試類，
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());
        //System.out.println(CacheManager.getSimpleFlag("ccc"));
        System.out.println("刪除前的大小："+CacheManager.getCacheSize());
        CacheManager.clearOnly("ccc");
        System.out.println("刪除前的大小："+CacheManager.getCacheSize());
        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("刪除前的大小："+CacheManager.getCacheSize());
        ArrayList myArrayList=CacheManager.getCacheAllkey();
        for(int i = 0;i < myArrayList.size(); i ++){
            System.out.println(myArrayList.get(i));
        }
        CacheManager.clearAll("a");
        System.out.println("刪除後的大小："+CacheManager.getCacheSize());
        CacheManager.getCacheAllkey();
    }
}