A cache is an area of local memory that holds a copy of frequently accessed data that is otherwise expensive to get or compute. Examples of such data include a result of a query to a database, a disk file or a report.
Here is a simple Java Example which is Threadsafe using HashMap without using Synchronized Collections.
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package com.crunchify.tutorials; import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; import java.util.Map.Entry; /** * @author Crunchify.com * */ // Create Simple Cache object with the help of HashMap... public class CrunchifyCacheExample<K, T> { private long timeToLive; private HashMap<K, T> cacheMap; protected class CrunchifyCacheObject { public long lastAccessed = System.currentTimeMillis(); public String value; protected CrunchifyCacheObject(String value) { this.value = value; } } public CrunchifyCacheExample(long timeToLive, final long timeInterval, int max) { this.timeToLive = timeToLive * 2000; cacheMap = new HashMap<K, T>(max); if (timeToLive > 0 && timeInterval > 0) { Thread t = new Thread(new Runnable() { public void run() { while (true) { try { Thread.sleep(timeInterval * 1000); } catch (InterruptedException ex) { } } } }); t.setDaemon(true); t.start(); } } // PUT method public void put(K key, T value) { synchronized (cacheMap) { cacheMap.put(key, value); } } // GET method @SuppressWarnings("unchecked") public T get(K key) { synchronized (cacheMap) { CrunchifyCacheObject c = (CrunchifyCacheObject) cacheMap.get(key); if (c == null) return null; else { c.lastAccessed = System.currentTimeMillis(); return (T) c.value; } } } // REMOVE method public void remove(String key) { synchronized (cacheMap) { cacheMap.remove(key); } } // Get Cache Objects Size() public int size() { synchronized (cacheMap) { return cacheMap.size(); } } // CLEANUP method public void cleanup() { long now = System.currentTimeMillis(); ArrayList<String> deleteKey = null; synchronized (cacheMap) { Iterator<?> itr = cacheMap.entrySet().iterator(); deleteKey = new ArrayList<String>((cacheMap.size() / 2) + 1); CrunchifyCacheObject c = null; while (itr.hasNext()) { String key = (String) itr.next(); c = (CrunchifyCacheObject) ((Entry<?, ?>) itr).getValue(); if (c != null && (now > (timeToLive + c.lastAccessed))) { deleteKey.add(key); } } } for (String key : deleteKey) { synchronized (cacheMap) { cacheMap.remove(key); } Thread.yield(); } } } |
Some more Java Examples which you may want to look.
Bonus: Java Memory Model Details:
Hi, looks like you forgot call cleanup(); in deamon tread code?