Spring全家桶(四)Bean的生命周期

十、Bean生命周期

10.1 Bean的生命周期

Spring IOC容器可以管理Bean的生命周期，也允许在Bean生命周期的特定点执行定制的任务。

Spring IOC容器对Bean的生命周期进行管理的过程如下：

1. 通过构造器或者工厂方法创建Bean实例
2. 为Bean的属性设置值和对其他Bean的引用
3. 调用Bean的初始化方法
4. 使用Bean
5. 容器关闭时，调用Bean的销毁方法

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

测试，创建一个Car类：

package com.stuspring.cycle;

/** * Created by bee on 17/4/26. */
public class Car {
    public Car() {
        System.out.println("Constructor....");
    }

    private String brand;

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

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

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

}

创建beans-cycle.xml并配置一个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" xmlns:p="http://www.springframework.org/schema/p" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="car" class="com.stuspring.cycle.Car" p:brand="Audi" init-method="initMethod" destroy-method="destoryMethod"/>
</bean

测试：

package com.stuspring.cycle;

import org.springframework.context.ApplicationContext;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/** * Created by bee on 17/4/26. */
public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-cycle.xml");
        Car car = (Car) ctx.getBean("car");
        System.out.println(car);
        ((ConfigurableApplicationContext) ctx).close();
    }
}

运行结果：

Constructor.... set Brand... init method.... com.stuspring.cycle.Car@604ed9f0 destory method...

10.2 Bean的后置处理器

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后置处理器会对IOC容器中的所有Bean实例逐一处理，要想针对特定Bean进行处理可以根据beanName参数进行判断。Bean后置处理器的典型应用是检查Bean属性的正确性或者根据特定的标准更改Bean的属性。

使用Bean后置处理器需要实现BeanPostProcessor接口，在Bean初始化方法被调用前后，Spring将把每个Bean实例分别传递给Bean接口的Object postProcessBeforeInitialization(Object bean, String beanName)和Object postProcessAfterInitialization(Object bean, String beanName)方法。

下面是测试例子：
新建一个Car类：

 package com.stuspring.cycle;

/** * Created by bee on 17/4/26. */
public class Car {
    private String brand;

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

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

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

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


    public String getBrand() {
        return brand;
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                '}';
    }
}

创建BeanPostProcessor的实现类：

package com.stuspring.cycle;

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

/** * Created by bee on 17/4/27. */
public class MyBeanPostProcessor implements BeanPostProcessor {
    public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException {
        System.out.println("postProcessBeforeInitialization: " + bean + "," + beanName);


        if ("car".equals(beanName)){
            Car car=new Car();
            car.setBrand("BaoMa");
            return car;
        }
        return bean;
    }

    public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException {

        System.out.println("postProcessAfterInitialization: " + bean + "," + beanName);
        return bean;
    }
}

创建Bean：

    <bean id="car" class="com.stuspring.cycle.Car" p:brand="Audi" init-method="initMethod"
          destroy-method="destoryMethod"/>
    <bean class="com.stuspring.cycle.MyBeanPostProcessor"/>

Main函数中测试：

package com.stuspring.cycle;

import org.springframework.context.ApplicationContext;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/** * Created by bee on 17/4/26. */
public class Main {

    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-cycle.xml");
        Car car = (Car) ctx.getBean("car");
        System.out.println(car.toString());
        System.out.println(car.getBrand());
        ((ConfigurableApplicationContext) ctx).close();
    }
}

运行结果：

Constructor.... set Brand... postProcessBeforeInitialization:    Car{brand='Audi'},car
Constructor.... set Brand... init method.... postProcessAfterInitialization: Car{brand='BaoMa'},car
Car{brand='BaoMa'}
BaoMa
destory method...

添加Bean的后置处理器以后Bean的生命周期如下;

1. 通过构造器或者工厂方法创建Bean实例
2. 为Bean的属性设置值和对其他Bean的引用
3. 将Bean实例传递给Bean后置处理器的postProcessBeforeInitialization方法
4. 调用Bean的初始化方法
5. 将Bean实例传递给Bean后置处理器的postProcessAfterInitialization方法
6. 使用Bean
7. 容器关闭时，调用Bean的销毁方法