对象池的容器：包含一个指定数量的对象。从池中取出一个对象时，它就不存在池中，直到它被放回。在池中的对象有生命周期：创建，验证，销毁，对象池有助于更好地管理可用资源，防止JVM内部大量临时小对象，频繁触发垃圾回收，造成系统暂停。有许多的使用示例。特别是在应用服务器数据源池，线程池等都是对象池的使用，下面情况适合使用对象池：
同样的对象高频率使用
对象太大消耗很多内存
对象初始化需要时间
对象内涉及IO操作 (Streams, Sockets, DB, etc.)
对象并不是线程安全时。
很多人使用 Apache Commons Pool.它有ObjectPool的接口，ObjectPoolFactory，PoolableObjectFactory和许多的实现。有addObject方法，borrowObject，invalidateObject，返回object添加，删除和返回对象。 PoolableObjectFactory定义对象池的操作行为，并提供各种回调。
但是Apache Commons Pool不是一个轻量开销的对象池，它很多方法采用了不建议使用的旧的Java的关键字synchronized。而Java 5中引入了Executor框架Java并发（多线程）。这里是最好的Executor框架。
package easypool; import java.util.concurrent.ConcurrentLinkedQueue; import java.util.concurrent.Executors; import java.util.concurrent.ScheduledExecutorService; import java.util.concurrent.TimeUnit; public abstract class ObjectPool<T> { private ConcurrentLinkedQueue<T> pool; private ScheduledExecutorService executorService; /** * Creates the pool. * * @param minIdle minimum number of objects residing in the pool */ public ObjectPool(final int minIdle) { // initialize pool initialize(minIdle); } /** * Creates the pool. * * @param minIdle minimum number of objects residing in the pool * @param maxIdle maximum number of objects residing in the pool * @param validationInterval time in seconds for periodical checking of minIdle / maxIdle conditions in a separate thread. * When the number of objects is less than minIdle, missing instances will be created. * When the number of objects is greater than maxIdle, too many instances will be removed. */ public ObjectPool(final int minIdle, final int maxIdle, final long validationInterval) { // initialize pool initialize(minIdle); // check pool conditions in a separate thread executorService = Executors.newSingleThreadScheduledExecutor(); executorService.scheduleWithFixedDelay(new Runnable() { @Override public void run() { int size = pool.size(); if (size < minIdle) { int sizeToBeAdded = minIdle - size; for (int i = 0; i < sizeToBeAdded; i++) { pool.add(createObject()); } } else if (size > maxIdle) { int sizeToBeRemoved = size - maxIdle; for (int i = 0; i < sizeToBeRemoved; i++) { pool.poll(); } } } }, validationInterval, validationInterval, TimeUnit.SECONDS); } /** * Gets the next free object from the pool. If the pool doesn\'t contain any objects, * a new object will be created and given to the caller of this method back. * * @return T borrowed object */ public T borrowObject() { T object; if ((object = pool.poll()) == null) { object = createObject(); } return object; } /** * Returns object back to the pool. * * @param object object to be returned */ public void returnObject(T object) { if (object == null) { return; } this.pool.offer(object); } /** * Shutdown this pool. */ public void shutdown() { if (executorService != null) { executorService.shutdown(); } } /** * Creates a new object. * * @return T new object */ protected abstract T createObject(); private void initialize(final int minIdle) { pool = new ConcurrentLinkedQueue<T>(); for (int i = 0; i < minIdle; i++) { pool.add(createObject()); } } }