使用Hashtable和线程技术制作自己简单的内存缓存

1. 首先,我们要做一个缓存数据类
  这个数据类要有一个数据成员,存放你的缓存数据,可以是一个类,也可以是一个List
  我们这里把它统一为Object
  然后要有一个过期时间,并且有一个访问次数,如果访问达到一定数量后,自动重置缓存

代码如下:

package zeus.cache.memory;

public class CacheData {
	private Object data;
	private long time;
	private int count;

	public CacheData() {

	}

	public CacheData(Object data, long time, int count) {
		this.data = data;
		this.time = time;
		this.count = count;
	}

	public CacheData(Object data) {
		this.data = data;
		this.time = System.currentTimeMillis();
		this.count = 1;
	}

	public void addCount() {
		count++;
	}

	public int getCount() {
		return count;
	}

	public void setCount(int count) {
		this.count = count;
	}

	public Object getData() {
		return data;
	}

	public void setData(Object data) {
		this.data = data;
	}

	public long getTime() {
		return time;
	}

	public void setTime(long time) {
		this.time = time;
	}
}

2.在有了缓存数据类以后,我们将建立一个缓存操作类

public class CacheOperation {
	private static CacheOperation singleton = null;

	private Hashtable cacheMap;// 存放缓存数据

	private ArrayList threadKeys;// 处于线程更新中的key值列表

	public static CacheOperation getInstance() {
		if (singleton == null) {
			singleton = new CacheOperation();
		}
		return singleton;
	}

	private CacheOperation() {
		cacheMap = new Hashtable();
		threadKeys = new ArrayList();
	}

     ...

}

我们看到这个缓存操作类是采用singleton模式的,因为我们的缓存可能要被多次调用,而
它只占用我们内存中的同一块空间,因为必须要采用singleton模式

增加缓存数据

/**
	 * 添加数据缓存 与方法getCacheData(String key, long intervalTime, int
	 * maxVisitCount)配合使用
	 * 
	 * @param key
	 * @param data
	 */
	public void addCacheData(String key, Object data) {
		addCacheData(key, data, true);
	}

	private void addCacheData(String key, Object data, boolean check) {
		if (Runtime.getRuntime().freeMemory() < 5L * 1024L * 1024L) {// 虚拟机内存小于10兆，则清除缓存
			// log.warn("WEB缓存：内存不足，开始清空缓存！");
			removeAllCacheData();
			return;
		} else if (check && cacheMap.containsKey(key)) {
			// log.warn("WEB缓存：key值= " + key + " 在缓存中重复, 本次不缓存！");
			return;
		}
		cacheMap.put(key, new CacheData(data));
	}

缓存获取机制就比较复杂,我们要判断该缓存是否过期,如果过期,就需要用后台线程重新获取
最新的缓存数据,而获取缓存数据的机制将是一个方法调用,这里方法可以通过反射来传进去

/**
	 * 些类存放方法的主调对像,名称及参数数组
	 * 
	 * @author master haku
	 * 
	 */
	public class MethodInfo {
		private Object o;
		private String methodName;
		private Object[] parameters;

		public MethodInfo(Object o, String methodName, Object[] parameters) {
			this.o = o;
			this.methodName = methodName;
			this.parameters = parameters;
		}

		public String getMethodName() {
			return methodName;
		}

		public void setMethodName(String methodName) {
			this.methodName = methodName;
		}

		public Object getO() {
			return o;
		}

		public void setO(Object o) {
			this.o = o;
		}

		public Object[] getParameters() {
			return parameters;
		}

		public void setParameters(Object[] parameters) {
			this.parameters = parameters;
		}

		public String toString() {
			StringBuffer str = new StringBuffer(methodName);
			if (parameters != null) {
				str.append("(");
				for (int i = 0; i < parameters.length; i++) {
					if (parameters[i] instanceof Object[]) {
						str.append(Arrays.toString((Object[]) parameters[i])).append(",");
					} else {
						str.append(parameters[i]).append(",");
					}
				}
				str.append(")");
			}
			return str.toString();
		}
	}

/**
	 * 线程调用方法
	 * 
	 * @author master haku
	 * 
	 */
	private class InvokeThread extends Thread {
		private Object o;
		private String methodName;
		private Object[] parameters;
		private String key;

		public InvokeThread(Object o, String methodName, Object[] parameters,
				String key) {
			this.o = o;
			this.methodName = methodName;
			this.parameters = parameters;
			this.key = key;
		}

		public void run() {
			threadKeys.add(key);
			invoke(o, methodName, parameters, key);
			threadKeys.remove(key);
		}
	}

/**
	 * 找不到完全匹配的方法时,对参数进行向父类匹配 因为方法aa(java.util.List) 与
	 * aa(java.util.ArrayList)不能自动匹配到
	 * 
	 * @param oc
	 * @param methodName
	 * @param pcs
	 * @return
	 * @throws NoSuchMethodException
	 * @throws NoSuchMethodException
	 */
	private Method matchMethod(Class oc, String methodName, Class[] pcs)
			throws NoSuchMethodException, SecurityException {
		try {
			Method method = oc.getDeclaredMethod(methodName, pcs);
			return method;
		} catch (NoSuchMethodException e) {
			Method[] ms = oc.getDeclaredMethods();
			aa: for (int i = 0; i < ms.length; i++) {
				if (ms[i].getName().equals(methodName)) {
					Class[] pts = ms[i].getParameterTypes();
					if (pts.length == pcs.length) {
						for (int j = 0; j < pts.length; j++) {
							if (!pts[j].isAssignableFrom(pcs[j])) {
								break aa;
							}
						}
						return ms[i];
					}
				}
			}
			throw new NoSuchMethodException();
		}
	}

更新缓存数据

/**
	 * 递归调用给定方法更新缓存中数据据
	 * 
	 * @param o
	 * @param methodName
	 * @param parameters
	 * @param key
	 * @return 若反射调用方法返回值为空则返回该值的类型
	 */
	private Object invoke(Object o, String methodName, Object[] parameters,
			String key) {
		Object returnValue = null;
		try {
			Class[] pcs = null;
			if (parameters != null) {
				pcs = new Class[parameters.length];
				for (int i = 0; i < parameters.length; i++) {
					if (parameters[i] instanceof MethodInfo) {// 参数类型是MethodInfo则调用该方法的返回值做这参数
						MethodInfo pmi = (MethodInfo) parameters[i];
						Object pre = invoke(pmi.getO(), pmi.getMethodName(),
								pmi.getParameters(), null);
						parameters[i] = pre;
					}
					if (parameters[i] instanceof Class) {
						pcs[i] = (Class) parameters[i];
						parameters[i] = null;
					} else {
						pcs[i] = parameters[i].getClass();
					}
				}
			}
			Class oc = o instanceof Class ? (Class) o : o.getClass();
			// Method m = oc.getDeclaredMethod(methodName, pcs);
			Method m = matchMethod(oc, methodName, pcs);
			returnValue = m.invoke(o, parameters);
			if (key != null && returnValue != null) {
				addCacheData(key, returnValue, false);
			}
			if (returnValue == null) {
				returnValue = m.getReturnType();
			}
		} catch (Exception e) {
			// log.error("调用方法失败,methodName=" + methodName);
			if (key != null) {
				removeCacheData(key);
				// log.error("更新缓存失败，缓存key=" + key);
			}
			e.printStackTrace();
		}
		return returnValue;
	}

根据键值获取缓存数据

/**
	 * 当缓存中数据失效时，用不给定的方法线程更新数据
	 * 
	 * @param o
	 *          取得数据的对像(该方法是静态方法是不用实例，则传Class实列)
	 * @param methodName
	 *          该对像中的方法
	 * @param parameters
	 *          该方法的参数列表(参数列表中对像都要实现toString方法,若列表中某一参数为空则传它所属类的Class)
	 * @param intervalTime
	 *          缓存的时间周期，小于等于0时不限制
	 * @param maxVisitCount
	 *          访问累积次数，小于等于0时不限制
	 * @return
	 */
	public Object getCacheData(Object o, String methodName, Object[] parameters,
			long intervalTime, int maxVisitCount) {
		Class oc = o instanceof Class ? (Class) o : o.getClass();
		StringBuffer key = new StringBuffer(oc.getName());// 生成缓存key值
		key.append("-").append(methodName);
		if (parameters != null) {
			for (int i = 0; i < parameters.length; i++) {
				if (parameters[i] instanceof Object[]) {
					key.append("-").append(Arrays.toString((Object[]) parameters[i]));
				} else {
					key.append("-").append(parameters[i]);
				}
			}
		}

		CacheData cacheData = (CacheData) cacheMap.get(key.toString());
		if (cacheData == null) {// 等待加载并返回
			Object returnValue = invoke(o, methodName, parameters, key.toString());
			return returnValue instanceof Class ? null : returnValue;
		}
		if (intervalTime > 0
				&& (System.currentTimeMillis() - cacheData.getTime()) > intervalTime) {
			daemonInvoke(o, methodName, parameters, key.toString());// 缓存时间超时,启动线程更新数据
		} else if (maxVisitCount > 0 && (maxVisitCount - cacheData.getCount()) <= 0) {// 访问次数超出,启动线程更新数据
			daemonInvoke(o, methodName, parameters, key.toString());
		} else {
			cacheData.addCount();
		}
		return cacheData.getData();
	}

/**
	 * 移除缓存中的数据
	 * 
	 * @param key
	 */
	public void removeCacheData(String key) {
		cacheMap.remove(key);
	}

	/**
	 * 移除所有缓存中的数据
	 * 
	 */
	public void removeAllCacheData() {
		cacheMap.clear();
	}

如何调用

先做一个缓存服务类

public class GtaHotelCacheService {
	public List<TGtahotel> getAllHotelList() {
		GtaHotelDao_Hib hotelDao = new GtaHotelDao_Hib();
		CacheOperation co = CacheOperation.getInstance();
		Object hotels = co.getCacheData(hotelDao, "getHotelList", new Object[]{},  3600*1000, 0);
		
		return (List<TGtahotel>)hotels;
	}
}

在控制台中测试,由于要体现缓存的价值,因为我们需要一个循环
这个循环根据用户选择才退出

public class ZeusCacheTest {
	public static void main(String[] args) {
		Scanner in;
		String key = "Y";
		PerformanceManager perf = null;
		
		while (key.toUpperCase().equals("Y")) {
			/* -- Performance Test Start -- */
	    perf = new PerformanceManager("Gta Hotel From Cache", new TimeConsole());
	    perf.Start();
	    /* -- Performance Test Start -- */
	    
			GtaHotelCacheService service = new GtaHotelCacheService();
			List<TGtahotel> hotels = service.getAllHotelList();
	
			displayHotels(hotels);
			
			/* -- Performance Test End -- */
	    perf.Stop();
	    perf.PrintTime();
	    /* -- Performance Test End -- */
	    
	    in = new Scanner(System.in);
			System.out.println("Try Again(Y/N): ");
			key = in.nextLine();
		}
	}

	private static void displayHotels(List<TGtahotel> hotels) {
    System.out.println("There are " + hotels.size() + " records.");
	}
}

输出结果:
There are 52973 records.
******************************* Performance Log *******************************
Module: Gta Hotel From Cache, Time Consumed: 0h:0m:6s:836ms
*******************************************************************************
Try Again(Y/N):
y
There are 52973 records.
******************************* Performance Log *******************************
Module: Gta Hotel From Cache, Time Consumed: 0h:0m:0s:0ms
*******************************************************************************