Config: via XML or Annotation

XML配置文件的每一个bean对应Annotation方式每一个java类，property name对应类字段，ref对应引用的其他类
XML配置和注解本质上相同，创建容器时用不同的应用上下文: ClassPathXmlApplicationContext和
AnnotationConfigApplicationContext, 传递参数分别为: XML文件 和 类对象

XML

config.xml:

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<?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-4.0.xsd ">

    <bean id="course" class="com.ssm.chap9.pojo.Course">
        <property name="module" ref="module" />
    </bean>

    <bean id="module" class="com.ssm.chap9.pojo.Module">
        <property name="assignment" ref="assignment" />
    </bean>

    <bean id="assignment" class="com.ssm.chap9.pojo.Assignment" />
</beans>

main:

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public class DemoCourse {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("config.xml");
        Course course = ctx.getBean(Course.class);
        course.getName();
    }
}

Annotation

AppContextCourse.java: 基于java配置和上面XML达到和上面XML相同的效果:

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import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppContextCourse {

    @Bean
    public Course course() {
        Course course = new Course();
        course.setModule("someModule");
        return course;
    }

    @Bean
    public Module module() {
        Module module = new Module();
        module.setAssignment("someAssignment");
        return module;
    }

    @Bean
    public Assignment assignment() {
        return new Assignment();
    }
}

main:

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public class DemoCourse {
    public static void main(String[] args) {
        ApplicationContext ctx = new AnnotationConfigApplicationContext(AppContextCourse.class);
        Course course = ctx.getBean(Course.class);
        course.getName();
    }
}

突然的感悟

Spring IoC的本质:

实际上是用XML配置文件控制javaBean的生产，而不用改java代码; “不写java代码”这一点，对应不用new主动创建对象而是用配置文件配置对应被动地生成对象，就是“控制反转”说法的来历；相当于“即插即拔”

而实际上,用java代码注解配置更多:annotation; 但是本质没有变: 没有用”new”创建Bean对象,所以用XML或者注解并没有影响IoC的实现

VVV below: not important

3 classes:

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public class Assignment {

}

public class Module {

    private String assignment;

    public String getAssignment() {
        return assignment;
    }

    public void setAssignment(String assignment) {
        this.assignment = assignment;
    }
}

public class Course {

    private String module;
    private String name; // course name

    public String getModule() {
        return module;
    }

    public void setModule(String module) {
        this.module = module;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}