【设计模式】【25】享元模式

应用场景

享元模式，英文名Flyweight Pattern

该模式通过对象复用，来避免大量创建复杂对象

主要用于线程池，连接池等场景，实现上比较简单

代码实现

	public class Product {
	
	}

	//每种类型的产品，共享一个对象
	public class ProductFactory {
	
	    //对象复用池
	    private static final Map pool = new HashMap();
	    //对象使用状态
	    private static final Map usage = new HashMap();
	
	    synchronized public static Product obtain(String type) {
	        //对象不存在，创建新对象
	        if (!pool.containsKey(type)) {
	            Product product = new Product();
	            pool.put(type, product);
	            usage.put(type, true);
	            return product;
	        }
	        //对象正在使用
	        if (usage.get(type))
	            throw new RuntimeException("object is in usage");
	        //复用旧对象
	        usage.put(type, true);
	        return pool.get(type);
	    }
	
	    //释放对象
	    synchronized public static void release(Product product) {
	        for (String type : pool.keySet())
	            if (pool.get(type) == product)
	                usage.put(type, false);
	    }
	}