Java框架spring Boot学习笔记（三）：Bean的作用域

Spring 框架Bean支持以下五个作用域:

下面介绍两种作用域，singleton和protoype

singleton作用域

singleton作用域为默认作用域，在同一个ioc容器内getBean是同一个bean，如果创建一个singleton作用域Bean定义的对象实例，该实例将存储在该Bean的缓存中，那么以后所有针对该 bean的请求和引用都返回缓存对象。

编写HelloWorld.java

 1 package com.example.spring;
 2
 3 public class HelloWorld {
 4     private String message;
 5     public void setMessage(String message){
 6         this.message  = message;
 7     }
 8     public void getMessage(){
 9         System.out.println("Your Message : " + message);
10     }
11 }

编写Beans.xml，设置为singleton作用域

1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5
6     <bean id="helloWorld" class="com.example.spring.HelloWorld" scope="singleton">
7     </bean>
8 </beans>

编写Application.java

 1 package com.example.spring;
 2
 3 import org.springframework.beans.factory.BeanFactory;
 4 import org.springframework.context.support.ClassPathXmlApplicationContext;
 5
 6 public class Application {
 7     public static void main(String[] args) {
 8         //bean配置文件所在位置 D:\\IdeaProjects\\spring\\src\\Beans.xml
 9         //使用BeanFactory容器
10         BeanFactory factory = new ClassPathXmlApplicationContext("file:D:\\IdeaProjects\\spring\\src\\Beans.xml");
11         HelloWorld objA = (HelloWorld)factory.getBean("helloWorld");
12         objA.setMessage("I‘m object A");
13         objA.getMessage();
14         HelloWorld objB = (HelloWorld) factory.getBean("helloWorld");
15         objB.getMessage();
16     }
17 }

运行输出

Your Message : I‘m object A
12:06:56.273 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Returning cached instance of singleton bean ‘helloWorld‘
Your Message : I‘m object A

prototype作用域

如果作用域设置为 prototype，每次创建对象实例只针对当前实例配置Bean，getBean是不同的bean。

将上述的Beans.xml，设置为prototype作用域

1 <?xml version="1.0" encoding="UTF-8"?>
2 <beans xmlns="http://www.springframework.org/schema/beans"
3        xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
4        xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
5
6     <bean id="helloWorld" class="com.example.spring.HelloWorld" scope="prototype">
7     </bean>
8 </beans>

运行输出：

Your Message : I‘m object A
13:52:03.767 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Creating instance of bean ‘helloWorld‘
13:52:03.767 [main] DEBUG org.springframework.beans.factory.support.DefaultListableBeanFactory - Finished creating instance of bean ‘helloWorld‘
Your Message : null