一般情况下,Spring 通过反射机制利用 <bean> 的 class 属性指定实现类实例化 Bean ,在某些情况下,实例化 Bean 过程比较复杂,如果按照传统的方式,则需要在 <bean> 中提供大量的配置信息。配置方式的灵活性是受限的,这时采用编码的方式可能会得到一个简单的方案。 Spring 为此提供了一个 org.springframework.bean.factory.FactoryBean 的工厂类接口,用户可以通过实现该接口定制实例化 Bean 的逻辑。

FactoryBean接口对于 Spring 框架来说占用重要的地位, Spring 自身就提供了 70 多个 FactoryBean 的实现。它们隐藏了实例化一些复杂 Bean 的细节,给上层应用带来了便利。从 Spring 3.0 开始, FactoryBean 开始支持泛型,即接口声明改为 FactoryBean<T> 的形式:

public interface FactoryBean<T> {

   /**
* Return an instance (possibly shared or independent) of the object
* managed by this factory.
* <p>As with a {@link BeanFactory}, this allows support for both the
* Singleton and Prototype design pattern.
* <p>If this FactoryBean is not fully initialized yet at the time of
* the call (for example because it is involved in a circular reference),
* throw a corresponding {@link FactoryBeanNotInitializedException}.
* <p>As of Spring 2.0, FactoryBeans are allowed to return {@code null}
* objects. The factory will consider this as normal value to be used; it
* will not throw a FactoryBeanNotInitializedException in this case anymore.
* FactoryBean implementations are encouraged to throw
* FactoryBeanNotInitializedException themselves now, as appropriate.
* @return an instance of the bean (can be {@code null})
* @throws Exception in case of creation errors
* @see FactoryBeanNotInitializedException
*/
T getObject() throws Exception; /**
* Return the type of object that this FactoryBean creates,
* or {@code null} if not known in advance.
* <p>This allows one to check for specific types of beans without
* instantiating objects, for example on autowiring.
* <p>In the case of implementations that are creating a singleton object,
* this method should try to avoid singleton creation as far as possible;
* it should rather estimate the type in advance.
* For prototypes, returning a meaningful type here is advisable too.
* <p>This method can be called <i>before</i> this FactoryBean has
* been fully initialized. It must not rely on state created during
* initialization; of course, it can still use such state if available.
* <p><b>NOTE:</b> Autowiring will simply ignore FactoryBeans that return
* {@code null} here. Therefore it is highly recommended to implement
* this method properly, using the current state of the FactoryBean.
* @return the type of object that this FactoryBean creates,
* or {@code null} if not known at the time of the call
* @see ListableBeanFactory#getBeansOfType
*/
Class<?> getObjectType(); /**
* Is the object managed by this factory a singleton? That is,
* will {@link #getObject()} always return the same object
* (a reference that can be cached)?
* <p><b>NOTE:</b> If a FactoryBean indicates to hold a singleton object,
* the object returned from {@code getObject()} might get cached
* by the owning BeanFactory. Hence, do not return {@code true}
* unless the FactoryBean always exposes the same reference.
* <p>The singleton status of the FactoryBean itself will generally
* be provided by the owning BeanFactory; usually, it has to be
* defined as singleton there.
* <p><b>NOTE:</b> This method returning {@code false} does not
* necessarily indicate that returned objects are independent instances.
* An implementation of the extended {@link SmartFactoryBean} interface
* may explicitly indicate independent instances through its
* {@link SmartFactoryBean#isPrototype()} method. Plain {@link FactoryBean}
* implementations which do not implement this extended interface are
* simply assumed to always return independent instances if the
* {@code isSingleton()} implementation returns {@code false}.
* @return whether the exposed object is a singleton
* @see #getObject()
* @see SmartFactoryBean#isPrototype()
*/
boolean isSingleton(); }

在该接口中还定义了以下3 个方法:

  • T getObject():返回由 FactoryBean 创建的 Bean 实例,如果 isSingleton() 返回 true ,则该实例会放到 Spring 容器中单实例缓存池中;
  • boolean isSingleton():返回由 FactoryBean 创建的 Bean 实例的作用域是 singleton 还是 prototype ;
  • Class<T> getObjectType():返回 FactoryBean 创建的 Bean 类型。

当配置文件中<bean> 的 class 属性配置的实现类是 FactoryBean 时,通过 getBean() 方法返回的不是 FactoryBean 本身,而是 FactoryBean#getObject() 方法所返回的对象,相当于 FactoryBean#getObject() 代理了 getBean() 方法。

测试:

package com.xiya.spring.beans.factorybean;

/**
* Created by N3verL4nd on 2017/3/20.
*/
public class Car {
private String brand;
private int price; public Car() {
} public Car(String brand, int price) {
this.brand = brand;
this.price = price;
} public String getBrand() {
return brand;
} public void setBrand(String brand) {
this.brand = brand;
} public int getPrice() {
return price;
} public void setPrice(int price) {
this.price = price;
} @Override
public String toString() {
return "Car{" +
"brand='" + brand + '\'' +
", price=" + price +
'}';
}
}
package com.xiya.spring.beans.factorybean;

import org.springframework.beans.factory.FactoryBean;

/**
* 通过 FactoryBean 来配置bean
* 需要实现 FactoryBean 接口
* Created by N3verL4nd on 2017/3/20.
*/
public class CarFactoryBean implements FactoryBean<Car> { private String brand; public void setBrand(String brand) {
this.brand = brand;
} public void fun() {
System.out.println("CarFactoryBean::fun()");
} //返回bean的对象
@Override
public Car getObject() throws Exception {
Car car = new Car(brand, 500000);
return car;
} //返回bean的类型
@Override
public Class<?> getObjectType() {
return Car.class;
} //返回bean是不是单实例
@Override
public boolean isSingleton() {
return true;
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!--
通过 FactoryBean 来配置 bean 的实例
class: 指向 FactoryBean 的全类名
property: 配置 FactoryBean 的属性
但实际返回的实例却是 FactoryBean 的 getObject()方法返回的实例。
-->
<bean id="car" class="com.xiya.spring.beans.factorybean.CarFactoryBean">
<property name="brand" value="BMW"/>
</bean>
</beans>

输出:

Car{brand='BMW', price=500000}

CarFactoryBean::fun()





Process finished with exit code 0

总之,当需要依赖现有的bean时,可以利用FactoryBean

三、通过 FactoryBean 来配置bean的更多相关文章

  1. Spring学习记录(十)---使用FactoryBean配置Bean

    之前学了,配置bean可以用普通全类名配置.用工厂方法配置,FactoryBean又是什么呢 有时候配置bean要用到,IOC其他Bean,这时,用FactoryBean配置最合适. FactoryB ...

  2. 通过FactoryBean配置Bean

    这是配置Bean的第三种方式,FactoryBean是Spring为我们提供的,我们先来看看源码: 第一个方法:public abstract T getObject() throws Excepti ...

  3. 4.spriing:Bean的生命周期/工厂方法配置Bean/FactoryBean

    1.Bean的生命周期 scope:singleton/prototype 1)spring容器管理singleton作用的生命周期,spring能够精确知道Bean合适创建,何时初始化完成,以及何时 ...

  4. Spring4.0学习笔记(7) —— 通过FactoryBean配置Bean

    1.实现Spring 提供的FactoryBean接口 package com.spring.facoryBean; import org.springframework.beans.factory. ...

  5. spring FactoryBean配置Bean

    概要: 实例代码具体解释: 文件夹结构 Car.java package com.coslay.beans.factorybean; public class Car { private String ...

  6. Spring配置bean的方法(工厂方法和Factorybean)

    通过工厂方法配置bean 通过调用静态工厂方法创建bean 通过静态工厂方法创建bean是将对象创建的过程封装到静态方法中.当客户端需要对象时,只需要简单地调用静态方法,而不关心创建对象的细节. 要声 ...

  7. spring4-2-bean配置-10-通过FactoryBean配置bean

    aaarticlea/png;base64,iVBORw0KGgoAAAANSUhEUgAAAk8AAAFHCAIAAAA3Hj/JAAAgAElEQVR4nO2dzdX0rA2Gp6asclwQTW

  8. Spring_通过 FactoryBean 配置 Bean

    beans-factorybean.xml <?xml version="1.0" encoding="UTF-8"?><beans xmln ...

  9. 12.Spring通过FactoryBean配置Bean

    为啥要使用FactoryBean: 在配置Bean的时候,需要用到IOC容器中的其它Bean,这个时候使用FactoryBean配置最合适. public class Car { private St ...

随机推荐

  1. linux技巧---创建应用快捷方式

    linux中启动或关闭应用有时候比较麻烦,你必须cd到该应用的可执行脚本的目录中再执行该脚本,不能在任意目录下开启或关闭应用..当然,设置了环境变量path可以解决在任意目录下开启应用的问题,但是每个 ...

  2. Wireshark抓包,带你快速入门

    前言 关于抓包我们平时使用的最多的可能就是Chrome浏览器自带的Network面板了(浏览器上F12就会弹出来).另外还有一大部分人使用Fiddler,Fiddler也是一款非常优秀的抓包工具.但是 ...

  3. CF1277A. Happy Birthday, Polycarp! 题解 枚举/数位DP

    题目链接:http://codeforces.com/contest/1277/problem/A 题目大意: 求区间 \([1,n]\) 范围内有多少只包含一个数字的数. 比如:\(1,77,777 ...

  4. 小小知识点(十八)U盘中病毒了,System Volume Information文件夹删除不掉

    win+R调出命令窗口后搜索cmd,启用cmd命令编辑器,并输入以下命令: attrib "H:\System Volume Information" -s   //这句话可以选择 ...

  5. 手把手带你了解消息中间件(2)——RabbitMQ

    RabbitMQ官网: http://www.rabbitmq.com/ Erlang官网:https://www.erlang.org 友情提示:RabbitMQ基于Erlang语言开发的,要想使用 ...

  6. python隐藏类中的属性

    方法一: 效果图一: 代码一: # 定义一个矩形的类 class Rectangle: # 定义初始化方法 def __init__(self,width,height): self.hidden_w ...

  7. USACO简介导论

      1000: USACO简介 时间限制: 1 Sec  内存限制: 128 MB提交: 8  解决: 7[提交] [状态] [讨论版] [命题人:外部导入] 题目描述 来源/分类 USACO-00  ...

  8. 弹性碰撞 poj 3684

    Simon is doing a physics experiment with N identical balls with the same radius of R centimeters. Be ...

  9. java intellij 工具的简单用法

    一.目录结构 1.新建项目(Empty Project) ->  新建module(可以有多个) => 出来src文件夹 -> 在src文件夹中新建package -> 在pa ...

  10. Qt Installer Framework翻译(5-0)

    创建安装程序 创建离线和在线安装程序,需要执行以下步骤: 为可安装组件创建一个package文件夹.有关更多信息,请参见包文件夹章节. 在config文件夹中创建一个名为config.xml的配置文件 ...