享元模式

享元模式：运用共享技术有效地支持大量细的对象，可以避免大量非常相似的开销。

在程序设计中，有时需要生成大量细度的类实例来表示数据。如果发现这些实例除了几个参数外基本上都是相同的。有时就能够受大幅度得减少需要实例化的类的数量。如果能把那些参数移到类实例的外面，在方法调用时讲它们传递进来，就可以通过共享大幅度地减少单个实例的数目。

package com.jerry.design.flyweight;
abstract class Conn {
	
	public abstract void getConn();

	
}

package com.jerry.design.flyweight;

import java.util.HashMap;
import java.util.Map;

public class ConnFactory {
	private Map<String, Conn> ConnPool = new HashMap<String, Conn>();

	private static ConnFactory connFactory = new ConnFactory();

	private ConnFactory() {
	}

	public static ConnFactory getInstance() {
	   return connFactory;
	}

	public Conn addConn(String name) {
		Conn conn = null;

	   if (ConnPool.containsKey(name)) { 
		   conn = ConnPool.get(name);
	   } else {
		   conn = new JdbcConn(name);
		   ConnPool.put(name, conn);
	   }
	   return conn;
	}

	public int getTotal() {
	   return ConnPool.size();
	}
}

package com.jerry.design.flyweight;
public class JdbcConn extends Conn {
	public String name;

	public JdbcConn(String name) {
	   this.name = name;
	}


	@Override
	public void getConn() {
		System.out.println("创建了一个" + name + "的jdbc连接。");
		
	}
  }

package com.jerry.design.flyweight;

import java.util.ArrayList;
import java.util.List;



	// 测试类
public class Test {
	private static List<Conn> conns = new ArrayList<Conn>();

	private static ConnFactory connFactory;

	// 增加订单
	private static void takeOrders(String name) {
		conns.add(connFactory.addConn(name));
	}

	public static void main(String[] args) {
		connFactory = ConnFactory.getInstance();

	   // 增加连接
	   takeOrders("Oracle");
	   takeOrders("sql server");
	   takeOrders("postgrep");
	   takeOrders("mysql");
	   takeOrders("mysql");
	   takeOrders("db2");
	   takeOrders("Oracle");
	   takeOrders("Oracle");
	   takeOrders("db2");
	   takeOrders("sql server");
	   takeOrders("postgrep");
	   takeOrders("db2");
	   takeOrders("sql server");
	   takeOrders("sql server");
	   takeOrders("postgrep");
	   for (Conn conn : conns) {
		   conn.getConn();
	   }

	   System.out.println("一共创建了 " + conns.size() + " 个连接! ");

	   System.out.println("共生成了 " + connFactory.getTotal()
	     + " 个Conn对象! ");
	}
}