Spring bean为什么需要依赖注入

Spring bean为什么需要依赖注入

目录具体步骤：样例1：样例2：Spring单例模式和原型模式一、单例模式二、原型模式思考 为什么需要依赖注入总结

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}

&ltgokDcFwai;dependency>

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

xmlns:xsi="http://w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://springframework.org/schema/beans http://springframework.org/schema/beans/spring-beans.xsd">

xmlns:xsi="http://w3.org/2001/XMLSchema-instance"

xsi:schemaLocation="http://springframework.org/schema/beans http://springframework.org/schema/beans/spring-beans.xsd">

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

1

2

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);

总结

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