@FactoryBean注解用法介绍

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