Spring 创建 Bean 的三种方式

在使用 Spring 框架后，对象以 Bean 的形式统一交给 IOC 容器去创建和管理。现阶段主流的方式是基于 SpringBoot 框架，基于注解的方式实现 Bean 的创建，但在原生 Spring 框架中其实存在三种创建 Bean 的方式。

一、基础类

1. BeanProcess 实体类，虽然加了 @Component 等三个注解，但只在注解方式创建 Bean 时用到了。

package com.nineya.spring.bean.register.entity;

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import javax.annotation.PreDestroy;

@Getter
@Setter
@ToString
@Component("test")
public class BeanProcess {
    private String name;
    
    @PostConstruct
    public void initMethod() {
        System.out.println("Bean InitMethodName: name = " + name);
    }

    @PreDestroy
    public void destroyMethod() {
        System.out.println("Bean DestroyMethodName: name = " + name);
    }
}

2. 后置处理器类

BeanFactoryPostProcessor 后置处理器。

package com.nineya.spring.bean.register.processor;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.stereotype.Component;

@Component
public class NineyaBeanFactoryPostProcessor implements BeanFactoryPostProcessor {

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        System.out.println("后置处理器BeanFactoryPostProcessor: postProcessBeanFactory");
    }
}

BeanPostProcessor 后置处理器。

package com.nineya.spring.bean.register.processor;

import org.springframework.beans.BeansException;
import org.springframework.beans.factory.config.BeanPostProcessor;
import org.springframework.stereotype.Component;

@Component
public class NineyaBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("后置处理器BeanPostProcessor: postProcessAfterInitialization(" + beanName + ") ：" + bean);
        return bean;
    }

    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("后置处理器BeanPostProcessor: postProcessBeforeInitialization(" + beanName + ") ：" + bean);
        return bean;
    }
}

二、三种创建方式

2.1 JavaApi 方式

JavaApi 方式没有注册 BeanFactoryPostProcessor 后置处理器的接口，应该在注册添加完所有 BeanDefinition 后，手动调用执行 BeanFactoryPostProcessor 后置处理器方法。

private static void javaApi() {
    // 创建bean工厂
    DefaultListableBeanFactory context = new DefaultListableBeanFactory();
    //构造bean定义
    GenericBeanDefinition gbd = new GenericBeanDefinition();
    gbd.setBeanClass(BeanProcess.class);
    // 设置属性
    List<PropertyValue> propertyValues = new ArrayList<>();
    propertyValues.add(new PropertyValue("name", "test"));
    gbd.setPropertyValues(new MutablePropertyValues(propertyValues));
    // 设置生命周期方法
    gbd.setInitMethodName("initMethod");
    gbd.setDestroyMethodName("destroyMethod");
    //注册到环境上下文
    context.registerBeanDefinition("test", gbd);
    context.addBeanPostProcessor(new NineyaBeanPostProcessor());
    new NineyaBeanFactoryPostProcessor().postProcessBeanFactory(context);
    // 通过class取得bean
    BeanProcess beanProcess = context.getBean(BeanProcess.class);
    System.out.println(beanProcess + " : " + beanProcess.hashCode());
}

2.2 xml方式

创建 bean 的 bean/register/spring.xml 文件。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
 http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean class="com.nineya.spring.bean.register.entity.BeanProcess" name="test" init-method="initMethod" destroy-method="destroyMethod">
        <property name="name" value="test" />
    </bean>

    <!-- 注册处理器 -->
    <bean class="com.nineya.spring.bean.register.processor.NineyaBeanPostProcessor"/>
    <bean class="com.nineya.spring.bean.register.processor.NineyaBeanFactoryPostProcessor"/>
</beans>

读取 xml 文件创建 bean 工厂。

private static void xmlFile() {
    ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("bean/register/spring.xml");
    // 通过class取得bean
    BeanProcess beanProcess = context.getBean(BeanProcess.class);
    System.out.println(beanProcess + " : " + beanProcess.hashCode());
}

2.3 注解方式

private static void annotation() {
    AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext();
    // 配置注解扫描路径
    context.scan(BeanRegisterMain.class.getPackage().getName());
    context.refresh();
    // 通过class取得bean
    BeanProcess beanProcess = context.getBean(BeanProcess.class);
    System.out.println(beanProcess + " : " + beanProcess.hashCode());
}