实战CGLib系列之proxy篇(四)：改进版延迟加载Dispatcher

作者shensy及出处http://shensy.iteye.com/blog/1884572

 

实战CGLib系列文章

本篇介绍改进版延迟加载器Dispatcher。

一、作用：

上一篇文章中，介绍了延迟加载器LazyLoader。本篇介绍另一种延迟加载接口Dispatcher。

Dispatcher接口同样继承于Callback，也是一种回调类型。

但是Dispatcher和LazyLoader的区别在于：LazyLoader只在第一次访问延迟加载属性时触发代理类回调方法，而Dispatcher在每次访问延迟加载属性时都会触发代理类回调方法。

二、示例：

与上篇文章相同，先定义一个实体类DispatcherBean，该Bean内有一个需要延迟加载的属性PropertyBean。PropertyBean的代码与上一篇相同，这里只看一下DispatcherBean：

public class DispatcherBean {
    private String name;
    private String value;
    private PropertyBean propertyBean;
    public DispatcherBean(){
        this.name="DispatcherBean";
        this.value="abc";
        this.propertyBean=createDispatcherBean();
    }
    protected PropertyBean createDispatcherBean(){
        Enhancer enhancer=new Enhancer();
        enhancer.setSuperclass(PropertyBean.class);
        return (PropertyBean)enhancer.create(PropertyBean.class,new ConcreteClassDispatcher());
    }
        //setter/getter
}

public class DispatcherBean {
	private String name;
	private String value;
	private PropertyBean propertyBean;
	public DispatcherBean(){
		this.name="DispatcherBean";
		this.value="abc";
		this.propertyBean=createDispatcherBean();
	}
	protected PropertyBean createDispatcherBean(){
		Enhancer enhancer=new Enhancer();
		enhancer.setSuperclass(PropertyBean.class);
		return (PropertyBean)enhancer.create(PropertyBean.class,new ConcreteClassDispatcher());
	}
        //setter/getter
}

同样对propertybean生成了代理类，回调类ConcreteClassDispatcher实现了Dispatcher接口，如下：

public class ConcreteClassDispatcher implements Dispatcher{
    public Object loadObject() throws Exception {
        System.out.println("Dispatcher loadObject ...");
        PropertyBean object=new PropertyBean();
        object.setPropertyName("PropertyBeanName!");
        object.setPropertyValue(1);
        return object;
    }
}

public class ConcreteClassDispatcher implements Dispatcher{
	public Object loadObject() throws Exception {
		System.out.println("Dispatcher loadObject ...");
		PropertyBean object=new PropertyBean();
		object.setPropertyName("PropertyBeanName!");
		object.setPropertyValue(1);
		return object;
	}
}

验证延迟加载：

DispatcherBean dispatcherBean=new DispatcherBean();
System.out.println(dispatcherBean.getName());
System.out.println(dispatcherBean.getValue());

PropertyBean pb=dispatcherBean.getPropertyBean();
System.out.println(pb.getPropertyName());
//在每次访问时都要进行回调
System.out.println(pb.getPropertyValue());

DispatcherBean dispatcherBean=new DispatcherBean();
System.out.println(dispatcherBean.getName());
System.out.println(dispatcherBean.getValue());

PropertyBean pb=dispatcherBean.getPropertyBean();
System.out.println(pb.getPropertyName());
//在每次访问时都要进行回调
System.out.println(pb.getPropertyValue());

控制台输出：

DispatcherBean
abc
Dispatcher loadObject ...
PropertyBeanName!
Dispatcher loadObject ...
1

DispatcherBean
abc
Dispatcher loadObject ...
PropertyBeanName!
Dispatcher loadObject ...
1

由此可见，每次获取property bean的属性都会自动触发回调方法加载对象。