FactoryBean使用示例

半兽人 发表于: 2018-01-11   最后更新时间: 2018-01-11 17:43:19  
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一般情况下，Spring通过反射机制利用bean的class属性指定实现类来实例化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框架来说占有重要的地位，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 的形式：

package org.Springframework.beans.factory;    
public interface FactoryBean<T> {    
   T getObject() throws Exception;    
   Class<?> getObjectType();    
   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 getObjectType()：返回FactoryBean创建的bean类型。

当配置文件中的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。例如：如果使用传统方式配置下面Car的时，Car的每个属性分别对应一个元素标签。

packagecom.systemnetpackage com.system.net.springFactory;

public class Car {
    private int maxSpeed;
    private String brand;
    privatevate intt maxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        thisvate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double pricevate int maxSpeed
    private int maxSpeed;
    private String brand;
    private double price
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed
    private int maxSpeed;
    private String brand;
    private doubleprivate
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed
    private int maxSpeed;
    private String brand;
    private double priceprivate
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed
    privateprivate
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public intprivate
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand private int
    private int maxSpeed;
    private String brand;
    private double price;

    public int
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String private
    private int maxSpeed;
    private String brand;
    private double price;

    public
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    publicprivate
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeedvate int maxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public Stringvate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(intvate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public voidvate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeedvate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed
    private int maxSpeedeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public  private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    publicvate int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice() {
        return price;
    }

    public  private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public
    private int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeedivate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrandrivate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return
    private
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrandrivate int
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void
    private int maxSpeed;
    private String brand;
    private double price;

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        this.brand = brand;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

如果用FactoryBean的方式实现就会灵活一些，下例通过逗号分割符的方式一次性地为Car的所有属性指定配置值：

package com.system.net.springFactory;

import org.springframework.beans.factory.FactoryBean;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class CarFactoryBean implements FactoryBean<Car> {

    private String carInfo;

    @Override
    public Car getObject() throws Exception {
        Car car = new Car();
        String[] infos = carInfo.split(",");
        car.setBrand(infos[0]);
        car.setMaxSpeed(Integer.valueOf(infos[1]));
        car.setPrice(Double.valueOf(infos[2]));
        return car;
    }

    @Override
    public Class<Car> getObjectType() {
        return Car.class;
    }

    @Override
    public boolean isSingleton() {
        return false;
    }

    public String getCarInfo() {
        return this.carInfo;
    }

    // 接受逗号分割符设置属性信息
    public void setCarInfo(String carInfo) {
        this.carInfo = carInfo;
    }
}

有了这个CarFactoryBean后，就可以在配置文件中使用下面这种自定义的配置方式配置Car Bean了：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="https://www.springframework.org/schema/beans"
       xmlns:xsi="https://www.w3.org/2001/XMLSchema-instance"
       xmlns:p="https://www.springframework.org/schema/p"
       xsi:schemaLocation="https://www.springframework.org/schema/beans
       https://www.springframework.org/schema/beans/spring-beans-2.5.xsd">

    <bean id="car" class="com.system.net.springFactory.CarFactoryBean" p:carInfo="benz,400,289000"/>
</beans>

运行测试

    public static void main(String[] args) {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(new String[]{"spring/applicationContext.xml"});
        // 正常情况
        Car car = (Car) context.getBean("car");
        System.out.println(car.getBrand());
        System.out.println(car.getMaxSpeed());
        System.out.println(car.getPrice());

        // 获取CarFactoryBean的实例
        CarFactoryBean carFactoryBean = (CarFactoryBean) context.getBean("&car");
        System.out.println(carFactoryBean.getCarInfo());
    }

当调用getBean("car")时，Spring通过反射机制发现CarFactoryBean实现了FactoryBean的接口，这时Spring容器就调用接口方法CarFactoryBean#getObject()方法返回。如果希望获取CarFactoryBean的实例，则需要在使用getBean(beanName) 方法时在beanName前显示的加上 "&" 前缀，例如getBean("&car")。

项目已分享到git上: https://github.com/orchome/net

更新于 2018-01-11
半兽人
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