弹簧范围差异答案

【问题标题】：Spring scopes differences弹簧范围差异
【发布时间】：2017-03-11 07:07:09
【问题描述】：

在 spring 作用域中，如果我使用单例，它会在执行逻辑之前加载配置文件时初始化所有 bean。但是如果我使用原型作为范围，bean 将根据调用进行初始化。对吗？单例是否作为静态变量和原型作为实例变量工作？

MainJava.java：

import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainJava {
public static void main(String arg[]){
AbstractApplicationContext applicationContext=new        ClassPathXmlApplicationContext("Beans.xml");
HelloWorld helloWorld=(HelloWorld) applicationContext.getBean("helloworld");
applicationContext.registerShutdownHook();
System.out.println(helloWorld.getMessage());

System.out.println("_________________________");

HelloWorld helloindia=(HelloWorld) applicationContext.getBean("helloindia");
System.out.println(helloindia.getMessage());
helloindia.setMessage("hello vishwa,thisa Bharat");
System.out.println(helloindia.getMessage());
System.out.println("_________________________");

HelloWorld hellonation=(HelloWorld) applicationContext.getBean("helloindia");
System.out.println(hellonation.getMessage());

 }
 }

HelloWorld.java：

     public class HelloWorld {
     private String message;

     public String getMessage() {
     return message;
     }

   public void setMessage(String message) {
   this.message = message;
    }

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

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

初始化HelloWorld.java：

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

  public class InitHelloWord implements BeanPostProcessor{

  @Override
  public Object postProcessAfterInitialization(Object bean, String beanName)     throws BeansException {
    System.out.println("after initalizing the bean "+beanName);
    return bean;
}

     @Override
     public Object postProcessBeforeInitialization(Object bean, String   beanName) throws BeansException {
    System.out.println("before initalizing the bean "+beanName);
    return bean;
   }

   }

Beans.xml：

  <?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-3.0.xsd">

     <bean name="helloworld" class="com.vishwa.bhat.HelloWorld" init-  method="init" destroy-method="destroy">
  <property name="message" value="hi vishwa,welcome to this world"> </property>
   </bean>

       <bean name="helloindia" class="com.vishwa.bhat.HelloWorld" scope="prototype" init-method="init" destroy-method="destroy">
     <property name="message" value="hi vishwa,welcome to India"></property>
    </bean>
     <bean class="com.vishwa.bhat.InitHelloWord"/>
    </beans>

如果作用域是单例则输出：

  before initalizing the bean helloworld
  initializing bean
  after initalizing the bean helloworld
  before initalizing the bean helloindia
  initializing bean
  after initalizing the bean helloindia
  hi vishwa,welcome to this world
  _________________________
  hi vishwa,welcome to India
  hello vishwa,thisa Bharat
  _________________________
 hello vishwa,thisa Bharat

 destroying bean
 destroying bean

范围原型的输出：

 before initalizing the bean helloworld
 initializing bean
after initalizing the bean helloworld
hi vishwa,welcome to this world
_________________________
before initalizing the bean helloindia
initializing bean
after initalizing the bean helloindia
hi vishwa,welcome to India
hello vishwa,thisa Bharat
_________________________
 before initalizing the bean helloindia
 initializing bean
  after initalizing the bean helloindia
 hi vishwa,welcome to India
 destroying bean

【问题讨论】：

标签： java spring

【解决方案1】：

ApplicationContext 默认加载单例模式。

ApplicationContext 实现的默认行为是在启动时急切地预实例化所有单例 bean。预实例化意味着 ApplicationContext 将急切地创建和配置其所有单例 bean，作为其初始化过程的一部分。通常这是一件好事，因为这意味着配置或周围环境中的任何错误都会立即被发现（而不是可能的数小时甚至数天）。

如果您需要重新定义单例的默认行为，只需指定 lazy-init="true"

【讨论】：