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=ERROR

applicationContext.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