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Spring系列（七）：@FactoryBean注解用法介绍

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Spring系列（七）：@FactoryBean注解用法介绍

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IT技术分享社区 2022-03-16 12:59:19 ©著作权

文章标签 spring java 数据 文章分类 Java 编程语言 阅读数265

​今天给大家介绍@FactoryBean注解用法，希望对大家能有所帮助！​

Spring系列（七）：@FactoryBean注解用法介绍_数据

​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​
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