Spring系列：@FactoryBean注解用法介绍

Posted 2022-03-17 IT技术分享社区

​今天给大家介绍@FactoryBean注解用法，希望对大家能有所帮助！​

​1、@FactoryBean注解介绍​

​FactoryBean是实现了FactoryBean<T>接口的Bean，可以该Bean的ID从BeanFactory中获取的实际上是FactoryBean中getObject()方法返回的实例对象，而并不是直接FactoryBean本身，想要获取FactoryBean对象本身，可以在id前面加一个&符号来获取。​

​BeanFactory部分代码：​

​说明：String FACTORY_BEAN_PREFIX = "&" ，&符号表示要获取FactoryBean本身​

package org.springframework.beans.factory;

import org.springframework.beans.BeansException;
import org.springframework.core.ResolvableType;
import org.springframework.lang.Nullable;

public interface BeanFactory 
    String FACTORY_BEAN_PREFIX = "&";

​2、@FactoryBean的源码内容如下：​

​Spring3.0版本之后，FactoryBean开始支持泛型，即接口声明改为FactoryBean<T>的形式​

package org.springframework.beans.factory;

import org.springframework.lang.Nullable;

public interface FactoryBean<T> 
    String OBJECT_TYPE_ATTRIBUTE = "factoryBeanObjectType";

    @Nullable
    T getObject() throws Exception;

    @Nullable
    Class<?> getObjectType();

    default boolean isSingleton() 
        return true;
    

​实现FactoryBean<T>接口有一下三个方法​

• ​getObject:获取bean对应的实例对象​
• ​getObjectType:获取factoryBean获取到的实例类型​
• ​isSingleton:factoryBean创建的实例是否是单实例​

​3、用法示例​

​3.1 新建Book.java​

package com.spring.bean;

public class Book 
    private String bookName;
    private String bookType;
    private double price;

    public Book(String bookName, String bookType, double price) 
        this.bookName = bookName;
        this.bookType = bookType;
        this.price = price;
    

    public String getBookName() 
        return bookName;
    

    public void setBookName(String bookName) 
        this.bookName = bookName;
    

    public String getBookType() 
        return bookType;
    

    public void setBookType(String bookType) 
        this.bookType = bookType;
    

    public double getPrice() 
        return price;
    

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

    @Override
    public String toString() 
        return "Book" +
                "bookName=" + bookName + \\ +
                ", bookType=" + bookType + \\ +
                ", price=" + price +
                ;
    

​3.2 新建BookFactoryBean.java​

package com.spring.bean;


import org.springframework.beans.factory.FactoryBean;


public class BookFactoryBean implements FactoryBean<Book> 
    public BookFactoryBean factoryBeanVO() 
        return new BookFactoryBean();
    

    public Book getObject() throws Exception 
        return new Book("红楼梦", "中国名著", 88);
    

    public Class<?> getObjectType() 
        return Book.class;
    

    public boolean isSingleton() 
        return true;
    

​3.3 FactoryBeanConfig.java​

package com.spring.config;

import com.spring.bean.BookFactoryBean;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class FactoryBeanConfig  
    @Bean
    public BookFactoryBean bookFactoryBean()
    
        return new BookFactoryBean();
    

​3.4 TestFactoryBean.java​

package com.spring.test;

import com.spring.config.FactoryBeanConfig;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class TestFactoryBean 

    public static void main(String[] args) 
        AnnotationConfigApplicationContext annotationContext = new AnnotationConfigApplicationContext(FactoryBeanConfig.class);
        // 获取工厂类的bean
        Object bookFactoryBean = annotationContext.getBean("bookFactoryBean");
        System.out.println(bookFactoryBean.getClass());
        // 输出结果： class com.spring.bean.Book
        //获取FactoryBean 本身 加 &符号
        Object bookFactoryBean1 = annotationContext.getBean("&bookFactoryBean");
        System.out.println(bookFactoryBean1.getClass());
        // 输出结果： class com.spring.bean.BookFactoryBean
    

​4、@FactoryBean应用场景​

• ​单一的对象使用FactoryBean意义不大。​
• ​创建对象时需要依赖于需要别的接口来监听数据、根据推送数据过来的接口做一些数据处理。​
• ​搭配其他接口协作, 依赖于Spring生命周期, 针对某个时间节点、合适的条件判断，来生成自己需要的对象。​

​5、典型应用​

• ​MyBatis3 提供 mybatis-spring项目中的 org.mybatis.spring.SqlSessionFactoryBean：​
• ​阿里开源的分布式服务框架 Dubbo 中的Consumer 也使用到了FactoryBean​
• ​shiro中ShiroFilterFactoryBean​
• ​druid的JdbcStatManagerFactoryBean​