Spring|Spring bean为什么需要依赖注入 Springbean为什么需要依赖注入

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-811115.3.11.18.204.12org.springframeworkspring-beans${spring.version}org.springframeworkspring-context${spring.version}org.projectlomboklombok${lombok.version}junitjunit${junit.version}

3.工程项目结构

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【Spring|Spring bean为什么需要依赖注入】
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; }@Overridepublic String toString() {return "Student{" +"number=" + number +", name='" + name + '\'' +", school='" + school + '\'' +'}'; }}

写一个配置文件

3.测试

@org.junit.Testpublic 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; }@Overridepublic 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; }@Overridepublic String toString() {return "Teacher{" +"name='" + name + '\'' +", school='" + school + '\'' +", studentList=" + studentList +", map=" + map +", set=" + set +'}'; }}

2.beans.xml

12

3.测试

@org.junit.Testpublic 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.Testpublic 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); }

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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.Testpublic 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); }

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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);

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