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 = "&";}
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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;
    }
}
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实现FactoryBean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 +
                '}';
    }
}
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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;
    }
}
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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();
    }
}
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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
    }
}
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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

Spring系列（七）：@FactoryBean注解用法介绍