Spring(bean为什么需要依赖注入)

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Spring,bean为什么需要依赖注入，恰卡网带你了解更多相关信息。

具体步骤：

1.创建一个maven项目 spring-day1-constructor

2.导入依赖

    
        UTF-8
        
        11
        11
        
        5.3.1
        1.18.20
        4.12
    
    
        
            org.springframework
            spring-beans
            ${spring.version}
        
        
            org.springframework
            spring-context
            ${spring.version}
        
        
            org.projectlombok
            lombok
            ${lombok.version}
        
        
            junit
            junit
            ${junit.version}

3.工程项目结构

样例1：

1.创建一个Student类

public class Student {
    private Long number;
    private String name;
    private String school;
    public void setNumber(Long number) {
        this.number = number;
    }
    public void setName(String name) {
        this.name = name;
    }
    public void setSchool(String school) {
        this.school = school;
    }
    public Student() {
    }
    public Student(Long number, String name, String school) {
        this.number = number;
        this.name = name;
        this.school = school;
    }
    @Override
    public String toString() {
        return "Student{" +
                "number=" + number +
                ", name='" + name + '\'' +
                ", school='" + school + '\'' +
                '}';
    }
}

写一个配置文件

3.测试

   @org.junit.Test
    public void testStudent(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Student student = applicationContext.getBean("s2", Student.class);
        System.out.println(student);
    }

样例2：

1.创建Teacher类

public class Teacher {
    private String name;
    private String school;
    private List studentList;
    private Map map;
    private Set set;
    public Teacher(String name, String school, List studentList, Map map, Set set) {
        this.name = name;
        this.school = school;
        this.studentList = studentList;
        this.map = map;
        this.set = set;
    }
    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + '\'' +
                ", school='" + school + '\'' +
                ", studentList=" + studentList +
                ", map=" + map +
                ", set=" + set +
                '}';
    }
}public class Teacher {
    private String name;
    private String school;
    private List studentList;
    private Map map;
    private Set set;
    public Teacher(String name, String school, List studentList, Map map, Set set) {
        this.name = name;
        this.school = school;
        this.studentList = studentList;
        this.map = map;
        this.set = set;
    }
    @Override
    public String toString() {
        return "Teacher{" +
                "name='" + name + '\'' +
                ", school='" + school + '\'' +
                ", studentList=" + studentList +
                ", map=" + map +
                ", set=" + set +
                '}';
    }
}

2.beans.xml

3.测试

    @org.junit.Test
    public void testTeacher(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Teacher teacher  = applicationContext.getBean("teacher", Teacher.class);
        System.out.println(teacher);
    }

Spring单例模式和原型模式

一、单例模式

Spring默认是单例模式的。

以Student的那个样例1 为例。 scope=“singleton” 加上这么一个设置当然默认也是它。

bean id="s1" class="com.crush.pojo.Student" scope="singleton">

这个时候我们来进行测试

    @org.junit.Test
    public void testStudent(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Student student1 = applicationContext.getBean("s1", Student.class);
        Student student2 = applicationContext.getBean("s1", Student.class);
        // 并且如果我们对其中一个做了修改 ，其余也会跟着一起被修改
        // 可以看到我们只修改了一个
        student1.setSchool("梦中的学校");
        System.out.println(student1);
        System.out.println(student2);
        System.out.println(student1==student2);
    }

二、原型模式

我们还是以**Student来做例子讲解 ** 注意：我们把原来设置改成了 scope=“prototype” 也就是原型模式

接着测试

    @org.junit.Test
    public void testStudent(){
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
        Student student1 = applicationContext.getBean("s2", Student.class);
        Student student2 = applicationContext.getBean("s2", Student.class);
        // 并且如果我们对其中一个做了修改 ，其余也会跟着一起被修改
        // 可以看到我们只修改了一个
        student1.setSchool("梦中的学校");
        System.out.println(student1);
        System.out.println(student2);
        System.out.println(student1==student2);
    }

思考为什么需要依赖注入

为什么我们以前用一个对象 new一下就好了，但用了Spring 之后，反而还需要写

这样一段代码再去获取勒？明明感觉更麻烦啦丫？用这个又有什么样的好处呢？

ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");
Student student1 = applicationContext.getBean("s2", Student.class);