[Spring IOC container] Bean life cycle

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Bean's life cycle

1. Concept

• In a nutshell, the life cycle of a bean is the process from object creation to object destruction.

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Second, the life cycle of the bean

(1) Create a bean instance through the constructor ( 无参数构造)

(2) Set values ​​for bean properties and reference to other beans ( 调用 set 方法)

(3) Call the method of bean initialization ( 进行配置初始化的方法)

(4) The bean can be used ( 对象获取)

(5) When the container is closed, call the method of destroying the bean ( 进行配置销毁的方法)

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Three, demonstrate the life cycle of the bean

Ⅰ. Create the Orders class

• Declare attributes
• Write a parameterless constructor
• Write the set() method
• Create initialization method
• Create bean destruction method

public class Orders {
    
    
    // 声明属性
    private String oName;

    // 1.无参构造
    public Orders() {
    
    
        System.out.println("第一步：执行无参构造器创建bean实例");
    }

    // 2.set
    public void setoName(String oName) {
    
    
        this.oName = oName;
        System.out.println("第二步：调用set方法设置属性的值");
    }

    // 3.创建执行的初始化的方法 --- 在xml文件中配置
    public void initMethod() {
    
    
        System.out.println("第三步：执行初始化的方法");
    }

    // 5.创建执行的bean销毁方法
    public void destroyMethod() {
    
    
        System.out.println("第五步：执行销毁方法");
    }
}

Ⅱ. Modify the configuration file

• Configure to create a bean object
• Add init-method属性, specify the initialization method
• Add destroy-method属性, specify the method of destroying the bean

<?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">

    <!-- 配置bean对象  -->
    <bean id="oders" class="Bean的生命周期.Orders" init-method="initMethod" destroy-method="destroyMethod">
        <property name="oName" value="电脑"></property>
    </bean>
</beans>

Ⅲ. Writing test classes

public class Test {
    
    
    @org.junit.Test
    public void test_orders(){
    
    
        try {
    
    
            ApplicationContext context = new ClassPathXmlApplicationContext("Bean的生命周期/bean_Orders.xml");
            // 4.获取bean实例对象
            Orders orders = context.getBean("orders",Orders.class);
            System.out.println("第四步：获取创建的bean实例对象");
            // 5.手动销毁bean实例对象
            ((ClassPathXmlApplicationContext)context).close();
        } catch (Exception e){
    
    
            e.getMessage();
        }
    }
}

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4. Bean's post processor, the bean life cycle has seven steps

(1) Create a bean instance through the constructor ( 无参数构造)

(2) Set values ​​for bean properties and reference to other beans ( 调用 set 方法)

• The method of passing the bean instance to the bean post processor postProcessBeforeInitialization

(3) Call the method of bean initialization ( 进行配置初始化的方法)

• The method of passing the bean instance to the bean post processor postProcessAfterInitialization

(4) The bean can be used ( 对象获取)

(5) When the container is closed, call the method of destroying the bean ( 进行配置销毁的方法)

▶ Demonstrate the effect of adding a post processor

(1) Create a class, implement the interface BeanPostProcessor, and create a post processor

public class MyBeanPost implements BeanPostProcessor {
    
    
    /**
     * 初始化之前调用
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
    
    
        System.out.println("在初始化之前执行的方法");
        return bean;
    }

    /**
     * 初始化之后调用
     * @param bean
     * @param beanName
     * @return
     * @throws BeansException
     */
    @Override
    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {
    
    
        System.out.println("在初始化之后执行的方法");
        return bean;
    }
}

(2) Modify the configuration file

• You only need to configure the bean object of the post processor class, becauseThe post-processor class implements the BeanPostProcessor接口post-processor, then the post-processor will add post-processor processing to all beans in the current configuration file。

<?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">

    <!-- 配置bean对象  -->
    <bean id="orders" class="Bean的生命周期.Orders" init-method="initMethod" destroy-method="destroyMethod">
        <property name="oName" value="电脑"></property>
    </bean>
    <!-- 配置后置处理器  -->
    <bean id="myBeanPost" class="Bean的生命周期.Test.MyBeanPost"></bean>
</beans>

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