以下仅是对map对方式讨论。没有对点阵图阵讨论。
作缓存要做以下2点:
1:清理及更新缓存时机的处理: . 虚拟机内存不足,清理缓存 .. 缓存时间超时,或访问次数超出, 启动线程更新 2:类和方法的反射 (线程嵌套调用) reflect.invoke的使用。
JAVA缓存有两种:
一、文件缓存,是指把数据存储在磁盘上,可以XML格式,也可以序列化文件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。
代码如下:内存中的缓存
package atest.hiyaCache; /** * * @author hiyachen * @version $Revision$ */ public class AddrDetail { public String latelyKeyword(String province, String city, String county){ System.out.println("AddrDetail.latelyKeyword=" + province + city + county); return province + city + county; } public String buildCache(String latelyKeyword){ System.out.println("AddrDetail.buildCache=" + latelyKeyword); return latelyKeyword; } }
package atest.hiyaCache; 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; } }
package atest.hiyaCache; import java.lang.reflect.Method; import java.util.ArrayList; import java.util.Arrays; import java.util.Hashtable; import org.apache.commons.logging.Log; //commons-loggings-1.1.1.jar import org.apache.commons.logging.LogFactory; public class CacheOperation { private static final Log log = LogFactory.getLog(CacheOperation.class); 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(); } /** * 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)); } /** * 取得缓存中的数据 * 与方法addCacheData(String key, Object data)配合使用 * @param key * @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(String key, long intervalTime, int maxVisitCount) { CacheData cacheData = (CacheData)cacheMap.get(key); if (cacheData == null) { return null; } if (intervalTime > 0 && (System.currentTimeMillis() - cacheData.getTime()) > intervalTime) { removeCacheData(key); return null; } if (maxVisitCount > 0 && (maxVisitCount - cacheData.getCount()) <= 0) { removeCacheData(key); return null; } else { cacheData.addCount(); } return cacheData.getData(); } /** * 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(); } /** * 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); Object o1 = oc.newInstance(); // add by chf returnValue = m.invoke(o1, 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; } /** * 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(); } } /** * 新启线程后台调用给定方法更新缓存中数据据 * @param o * @param methodName * @param parameters * @param key */ private void daemonInvoke(Object o, String methodName,Object[] parameters, String key) { if (!threadKeys.contains(key)) { InvokeThread t = new InvokeThread(o, methodName, parameters, key); t.start(); } }
/** * 些类存放方法的主调对像,名称及参数数组 * @author hiya * */ 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 hiya * */ 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); } } /** * 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(); } public String toString() { StringBuffer sb = new StringBuffer("************************ "); sb.append("正在更新的缓存数据: "); for (int i = 0; i < threadKeys.size(); i++) { sb.append(threadKeys.get(i)).append(" "); } sb.append("当前缓存大小:").append(cacheMap.size()).append(" "); sb.append("************************"); return sb.toString(); } }
实际使用:
package atest.hiyaCache; //import javax.swing.text.Document; import atest.hiyaCache.CacheOperation.MethodInfo; public class CacheExec { /** * @param args */ public static void main(String[] args) {// String province = request.getParameter("province"); // String city= request.getParameter("city"); // String county= request.getParameter("county"); // Document doc = XMLBuilder.buildLatelyKeyword(kwm.latelyKeyword(province, city, county)); // out.write(doc); String province = "Jiangsu "; String city= "Nanjing "; String county= "Jiangning"; CacheOperation co = CacheOperation.getInstance(); // MethodInfo mi = co.new MethodInfo(kwm, "latelyKeyword", new Object[]{province, city, county}); // Document doc = (Document )co.getCacheData(XMLBuilder.class,"buildLatelyKeyword",new Object[]{mi}, 120000, 0); // out.write(doc); while (true){ // [email protected] MethodInfo mi = co.new MethodInfo(AddrDetail.class, "latelyKeyword", new Object[]{province, city, county}); // 120000 毫秒(2分钟)更新缓存 String aa = (String)co.getCacheData(AddrDetail.class,"buildCache",new Object[]{mi}, 120000, 5); System.out.println("CacheExec:main=" + aa); } } }
当缓存次数超过5时,重新执行。看一下执行结果。
AddrDetail.latelyKeyword=Jiangsu Nanjing Jiangning AddrDetail.buildCache=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning AddrDetail.latelyKeyword=Jiangsu Nanjing Jiangning AddrDetail.buildCache=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning CacheExec:main=Jiangsu Nanjing Jiangning AddrDetail.latelyKeyword=Jiangsu Nanjing Jiangning AddrDetail.buildCache=Jiangsu Nanjing Jiangning
大数据量的缓存肯定还是要保存到文件,这个时候光用JDK来实现就比较复杂了,这里当然要用到第三方开源框架来实现了,常用的有Oscache,Ehcache,Jcache,Jbosscache等等很多,推荐还是Ehcache与Oscache,hibernate采用了Ehcache做为其缓存机制默认实现,Oscache没深入研究,但是Ibatis推荐的缓存为这个。
为什么要缓存,无非就是节省访问时间已经大并发量带来的访问上资源的消耗,这个资源有软资源和硬资源,做java的几乎每天都在有意识或者无意识的跟缓存打交道,最常见的缓存,Connection Pool,还有IOC其实也算一个。
缓存用的好能提高性能,用的不好反而会急剧的降低产品的性能,就拿hibernate来说,hibernate性能肯定不如jdbc,但是缓存用的好的话增删改查的性能相差无几,hibernate缓存最核心的部分个人觉得在于对象的有效性,缓存的命中率越高意味着性能越高,命中率跟缓存对象的有效性息息相关,如何保证对象有效这个很难,也很有搞头,如果缓存中对象有效性很差,其性能甚至会低于不用缓存,因为缓存本身就会耗性能跟资源,缓存的对象很多都很快失效了无疑得不偿失,还有缓存的深度也有讲究,这个深度是指从页面到数据库,显然是页面缓存的性能最好,因为调用页面缓存消耗的资源最少,当然现实中是不可能有太多页面缓存的。