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";@NullableT getObject() throws Exception;@NullableClass<?> 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;}@Overridepublic 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  {@Beanpublic 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beanObject 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

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