Java Spring-Bean的生命周期

Spring IOC容器对Bean的生命周期进行管理的过程:

通过构造器或工厂方法创建Bean实例

为Bean的属性设置值和对其他Bean的引用

调用Bean的初始化方法

Bean可以使用了

当容器关闭时，调用Bean的销毁方法

在Bean的声明里设置init-method和destroy-method属性，为Bean指定初始化和销毁方法。

    <bean id="car" class="com.cloud.spring.beans.cycle.Car"
    init-method="init2"
    destroy-method="destory"
    >
        <property name="brand" value="Audi"></property>
    </bean>
    
    public class Car {

    private String brand;

    public Car() {
        System.out.println("Car's Constructor...");
    }

    public String getBrand() {
        return brand;
    }

    public void setBrand(String brand) {
        System.out.println("setBrand...");
        this.brand = brand;
    }

    public void init2(){
        System.out.println("init...");
    }

    public void destory(){
        System.out.println("destroy...");
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                '}';
    }
}
//输出
Car's Constructor...
setBrand...
init...
com.cloud.spring.beans.cycle.Car@77caeb3e
destroy...

Bean后置处理器允许在调用初始化方法前后对Bean进行额外的处理。Bean后置处理器对IOC容器里的所有Bean实例逐一处理，而非单一实例，其典型应用是:检查Bean属性的正确性或根据特定的标准更改Bean的属性。对Bean后置处理器而言，需要实现Interface BeanPostProcessor接口，在初始化方法被调用前后，Spring将把每个Bean实例分别传递给上述接口的以下两个方法:

Object postProcessAfterInitialization(Object bean,String beanName);
Object postProcessBeforeInitialization(Object bean,String beanName);

例子

    <bean id="car" class="com.cloud.spring.beans.cycle.Car"
    init-method="init2"
    destroy-method="destory"
    >
        <property name="brand" value="Audi"></property>
    </bean>

    <!-- 配置bean的后置处理器 -->
    <bean class="com.cloud.spring.beans.cycle.MyBeanPostProcessor"></bean>
    
    public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException{
        System.out.println("postProcessBeforeInitialization: " + bean + "," + beanName);
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException{
        System.out.println("postProcessAfterInitialization: " + bean + "," + beanName );
        return bean;
    }
}

        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("beans-cycle.xml");
        Car car = (Car)context.getBean("car");
        System.out.println(car);

        //关闭IOC容器
        context.close();
//输出
Car's Constructor...
setBrand...
postProcessBeforeInitialization: Car{brand='Audi'},car
init...
postProcessAfterInitialization: Car{brand='Audi'},car
Car{brand='Audi'}
destroy...

在postProcessAfterInitialization方法中处理返回Bean，最后改变生成的bean。

public class MyBeanPostProcessor implements BeanPostProcessor {
    @Override
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException{
        System.out.println("postProcessBeforeInitialization: " + bean + "," + beanName);
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException{
        System.out.println("postProcessAfterInitialization: " + bean + "," + beanName );
        Car car = new Car();
        car.setBrand("Ford");
        return car;
    }
}
//输出
Car's Constructor...
setBrand...
postProcessBeforeInitialization: Car{brand='Audi'},car
init...
postProcessAfterInitialization: Car{brand='Audi'},car
Car's Constructor...
setBrand...
Car{brand='Ford'}
destroy...

    <bean id="car" class="com.cloud.spring.beans.cycle.Car"
    init-method="init2"
    destroy-method="destory"
    >
        <property name="brand" value="Audi"></property>
    </bean>
<!-- 实现BeanPostProcessor接口，并具体提供
     Object postProcessBeforeInitialization(Object bean,String beanName): init-method 之前被调用
     Object postProcessAfterInitialization(Object bean,String beanName):init-method 之后被调用
     的实现

     bean:bean 实例本身
     beanName:IOC 容器配置的bean的名字
     返回值:是实际上放回给用户的那个Bean，注意:可以在以上两个方法中修改返回的bean，甚至返回一个新的bean
-->
    <!-- 配置bean的后置处理器 -->
    <bean class="com.cloud.spring.beans.cycle.MyBeanPostProcessor"></bean>

添加Bean后置处理器后Bean的生命周期

Spring IOC容器对Bean的生命周期进行管理的过程:

通过构造器或工厂方法创建Bean实例

为Bean的属性设置值和对其他Bean的引用

将Bean实例传递给Bean后置处理器的postProcessBeforeInitialization方法

调用Bean的初始化方法

将Bean实例传递给Bean后置处理器的postProcessAfterInitialization方法

Bean可以使用了

当容器关闭时，调用Bean的销毁方法