说明

解决问题：
系统中存在多个相同对象,需要共享一份对象的拷贝,而不是每一次使用都要创建对象。

好处：[复用大对象、节省内存空间和对象创建时间]
1.节省重复创建对象的开销,享元对象只会被创建一次。
2.创建数量少，系统内存需求减少，gc的压力也会降低。

注意点：
1.享元工厂维护享元对象，提供对外获取对象的方法

实现方式：
参考FlyWeight下的实现

享元对象是不可相互替换的。对象池中的对象都是等价的，比如数据库连接池。

源码实践

享元接口

package xin.rtime.design.flyweight;
// 享元接口
public interface IFlyWeight {
    String method();
}

接口实现

package xin.rtime.design.flyweight;
// 享元对象实现
public class FlyWeightImpl implements IFlyWeight {
    @Override
    public String method() {
        return "method";
    }
}

享元工厂

package xin.rtime.design.flyweight;
import java.util.HashMap;
import java.util.Map;
// 享元工厂
// 职能： 维护享元对象
public class FlyWeightFactory {
    private FlyWeightFactory() {}
    private Map<String,IFlyWeight> flyweights =new HashMap<String,IFlyWeight>();
    // 获取享元对象
    public IFlyWeight getFlyWeight(String tenantId) {
        IFlyWeight flyWeight = flyweights.get(tenantId);
        if(flyWeight == null) {
            flyWeight = new FlyWeightImpl();
            flyweights.put(tenantId, flyWeight);
        }
        return flyWeight;
    }
    public static FlyWeightFactory getInstance() {
        return FlyWeightFactoryHodler.instance;
    }
    private static class FlyWeightFactoryHodler {
        private static FlyWeightFactory instance = new FlyWeightFactory();
    }
}

验证

package xin.rtime.design;

import xin.rtime.design.flyweight.FlyWeightFactory;
import xin.rtime.design.flyweight.IFlyWeight;

public class FlyWeightTest {

    public static void main(String[] args) {

        FlyWeightFactory factory = FlyWeightFactory.getInstance();
        IFlyWeight flyWeight = factory.getFlyWeight("test");
        System.out.println(flyWeight.method());

    }
}