spring学习45-spring的单例bean

pom.xml
    <?xml version="1.0" encoding="UTF-8"?>
     <project xmlns="http://maven.apache.org/POM/4.0.0"
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
              xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
         <modelVersion>4.0.0</modelVersion>
         <groupId>com.geyao</groupId>
         <artifactId>spring01geyao</artifactId>
         <version>1.0-SNAPSHOT</version>
         <dependencies>
             <dependency>
                 <groupId>org.springframework</groupId>
                 <artifactId>spring-context</artifactId>
                 <version>4.3.13.RELEASE</version>
             </dependency>
             <dependency>
                 <groupId>org.springframework</groupId>
                 <artifactId>spring-test</artifactId>
                 <version>3.2.0.RELEASE</version>
             </dependency>
             <dependency>
                 <groupId>log4j</groupId>
                 <artifactId>log4j</artifactId>
                 <version>1.2.17</version>
             </dependency>
             <dependency>
                 <groupId>junit</groupId>
                 <artifactId>junit</artifactId>
                 <version>4.12</version>
             </dependency>
             <dependency>
                 <groupId>org.springframework</groupId>
                 <artifactId>spring-test</artifactId>
                 <version>4.3.4.RELEASE</version>
                 <scope>test</scope>
             </dependency>
             <dependency>
                 <groupId>org.springframework</groupId>
                 <artifactId>spring-test</artifactId>
                 <version>4.3.4.RELEASE</version>
                 <scope>test</scope>
             </dependency>
         </dependencies>
     </project>log4j.properties
    ### 设置###
     log4j.rootLogger = ERROR,stdout
     ### 输出信息到控制抬 ###
     log4j.appender.stdout = org.apache.log4j.ConsoleAppender
     log4j.appender.stdout.layout = org.apache.log4j.PatternLayout
     log4j.appender.stdout.layout.ConversionPattern = [%-5p] %d{yyyy-MM-dd HH:mm:ss,SSS} method:%l%n%m%n
     log4j.category.org.springframework.beans.factory=ERRORapplicationContext.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.xsd">
         <!--
         bean元素：描述当前的对象需要由spring容器管理
         id属性：标识对象 未来在应用程序中可以根据id获取对象
         class对象：被管理的对象的全名
        -->
         <bean id="notepad" class="com.geyao.demo.NotePad"/>
     </beans>notepad类
    package com.geyao.demo;
     public class NotePad {
         public NotePad() {
             super();
             System.out.println("NotePad的构造函数"+this.toString());
         }
     }Notepadtest类
    package com.geyao.demo;
     import org.junit.Test;
     import org.springframework.context.support.ClassPathXmlApplicationContext;
     //无论我们是否去主动获取对象，spring上下文刚加载就会创建对象
     //无论获取多少次，都是统一对象
     //
     public class NotepadTest {
         @Test
         public void test01(){
             ClassPathXmlApplicationContext context=new ClassPathXmlApplicationContext("applicationContext.xml");
            NotePad notePad1= (NotePad)context.getBean("notepad");
             NotePad notePad2= (NotePad)context.getBean("notepad");
             System.out.println(notePad1=notePad2);
         }
     }notepadtestAuto类
    package com.geyao.demo;
     import org.junit.Test;
     import org.junit.runner.RunWith;
     import org.springframework.beans.factory.annotation.Autowired;
     import org.springframework.test.context.ContextConfiguration;
     import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
     @RunWith(SpringJUnit4ClassRunner.class)
     @ContextConfiguration("classpath:applicationContext.xml")
     public class NotePadTestAuto {
         @Autowired
         private NotePad notePad1;
         @Autowired
         private NotePad notePad2;
         @Test
         public void test01(){
             System.out.println(notePad1==notePad2);
         }
     }运行结果
    NotePad的构造函数com.geyao.demo.NotePad@20ccf40b
     true