Spring笔记(二)：bean的作用域

在bean中配置作用域使用属性scope来设置bean的作用域

• scope="singleton" 也是bean配置中默认的配置

  bean配置文件代码:

   <bean id="school" class="com.example.demo.entity.School" scope="singleton">
      <property name="schoolName" value="北京大学"></property>
      <property name="schoolAddress" value="北京市海淀区"></property>
  </bean>
  

  java测试代码：

      ApplicationContext ctx = new ClassPathXmlApplicationContext("bean-scop.xml");
  
      School school = (School) ctx.getBean("school");
      School school1 = (School) ctx.getBean("school");
  
      System.out.println(school);
      System.out.println(school1);     
  

  运行结果:

  School被创建
  Disconnected from the target VM, address: '127.0.0.1:51820', transport: 'socket'
  com.example.demo.entity.School@4d5650ae
  com.example.demo.entity.School@4d5650ae
  
  Process finished with exit code 0
  

  从上可以看出bean属性scope为singleton时，容器初始化时会创建实例，该容器中对象的实例有且只有一个

• scope="prototype"

  bean配置：

   <bean id="school1" class="com.example.demo.entity.School" scope="prototype">
      <property name="schoolName" value="清华大学"></property>
      <property name="schoolAddress" value="北京市海淀区"></property>
  </bean>
  

  java测试代码：

   ApplicationContext ctx = new ClassPathXmlApplicationContext("bean-scop.xml");
  
      School school = (School) ctx.getBean("school1");
      School school1 = (School) ctx.getBean("school1");
  
      System.out.println(school);
      System.out.println(school1);
  
  

  运行结果：

  School被创建
  School被创建
  com.example.demo.entity.School@a38c7fe
  com.example.demo.entity.School@6fdbe764
  

  从运行结果可以看出bean属性scope为prototype时，容器初始化时不会创建bean的实例，只有在调用时才会创建bean的实例；

• scope="request" 和 scope="session"
  这两个属性都是涉及到与对象，一个是resquest域，两一个是session域