Spring Bean实例化实现过程解析

这篇文章主要介绍了Spring Bean实例化实现过程解析,文中通过示例代码介绍的非常详细,对大家的学习或者工作具有一定的参考学习价值,需要的朋友可以参考下

Bean的实例化

1.构造器实例化:Spring容器通过Bean对应类中默认的无参构造方法来实例化Bean

package com.itheima.instance.constructor;

public class Bean1 {

}

<?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 id="bean1" class="com.itheima.instance.constructor.Bean1"></bean>

</beans>

在beans1.xml文件中,定义了一个id为bean1的Bean,并通过class属性指定其对应的实现类Bean1

package com.itheima.instance.constructor;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InstanceTest1 {

public static void main(String[] args) {

//定义配置文件路径

String xmlPath = "com/itheima/instance/constructor/beans1.xml";

//ApplicationContext在加载配置文件时,对Bean进行实例化

ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);

Bean1 bean = (Bean1) applicationContext.getBean("bean1");

System.out.println(bean);

}

}

在InstanceTest1类中,首先定义了配置文件的路径,然后Spring容器ApplicationContext会加载配置文件。在加载时,Spring容器会通过id为bean1的实现类Bean1中默认的无参构造方法对Bean进行实例化。

2. 静态工厂方法实例化

package com.itheima.instance.static_factory;

public class Bean2 {

}

package com.itheima.instance.static_factory;

public class MyBean2Factory {

//使用自己的方法创建Bean2实例

public static Bean2 createBean(){

return new Bean2();

}

}

<?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 id="bean2" class="com.itheima.instance.static_factory.MyBean2Factory" factory-method="createBean"></bean>

</beans>

定义id为bean2的Bean,通过class属性指定其对应的工厂实现类(MyBean2Factory.java),需要增加factory-method属性来告诉Spring容器其方法名称为createBean。

package com.itheima.instance.static_factory;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InstanceTest2 {

public static void main(String[] args) {

//定义配置文件路径

String xmlPath = "com/itheima/instance/static_factory/beans2.xml";

//ApplicationContext在加载配置文件时,对Bean进行实例化

ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);

System.out.println(applicationContext.getBean("bean2"));

}

}

3.实例工厂方式实例化

package com.itheima.instance.factory;

public class Bean3 {

}

package com.itheima.instance.factory;

public class MyBean3Factory {

public MyBean3Factory(){

System.out.println("bean3工厂实例化中");

}

//创建Bean3实例的方法

public Bean3 createBean(){

return new Bean3();

}

}

<?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 id="myBean3Factory" class="com.itheima.instance.factory.MyBean3Factory"></bean>

<!-- 使用 factory-bean属性指向配置的实例工厂

使用factory-method属性确定使用工厂中的哪个方法 -->

<bean id="bean3" factory-bean="myBean3Factory" factory-method="createBean"></bean>

</beans>

首先配置了一个工厂Bean,然后配置了需要实例化的Bean。在id为bean3的Bean中,使用factory-bean属性指向配置的实例工厂,使用factory-method属性来确定使用工厂中的createBean()方法

package com.itheima.instance.factory;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InstanceTest3 {

public static void main(String[] args) {

//指定配置文件路径

String xmlPath = "com/itheima/instance/factory/beans3.xml";

//ApplicationContext加载配置文件时,对Bean进行实例化

@SuppressWarnings("resource")

ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);

System.out.println(applicationContext.getBean("bean3"));

}

}

以上是 Spring Bean实例化实现过程解析 的全部内容, 来源链接: utcz.com/z/339212.html

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