Spring DI依赖注入

• setter设置注入（保证类中有提供setter方法）
• 构造器注入
• 命名空间注入

1、项目结构

image.png

1.1 pom.xml

<dependencies>
        <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>5.1.5.RELEASE</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework/spring-beans -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-beans</artifactId>
            <version>5.1.5.RELEASE</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>5.1.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.12</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

1.2 Teahcer

public class Teacher {
  private String name ;
   private int age;
  //省略getter setter方法
}

1.3 Course

public class Course {
    private String courseName;
    private int courseHours;
    private Teacher teacher;
  //省略getter setter方法
}

2、setter方法注入

2.1 bean.xml

  <bean id="teacher" class="com.springdi.Teacher">
        <property name="age" value="22"></property>
        <property name="name" value="HeloWxl"></property>
    </bean>

    <bean id="course" class="com.springdi.Course">
        <property name="courseHours" value="100"></property>
        <property name="teacher" ref="teacher"></property>
        <property name="courseName" value="Java"></property>
    </bean>

• Value:表示的是给name所表示的简单类型的属性赋值（如String,int）
• Ref:表示的是“自定义类型”的对象属性赋值（如这里的Teacher）,ref值的另一个bean的id值，从而实现多个bean之间的相互引用，相互依赖的关系

2.2 测试类

    @Test
    public void testDi(){
        //从spring容器获得 //1 获得容器
        String xmlPath="bean.xml";
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext(xmlPath);

        //2获得内容 --不需要自己new，都是从spring容器获得
        Teacher teacher = (Teacher) applicationContext.getBean("teacher");
        System.out.println(teacher.toString());

        Course course = (Course) applicationContext.getBean("course");
        course.showInfo();
    }

2.3 测试结果

image.png

3、构造器注入

3.1 Course里面进行添加有参构造函数

  public Course(){
    }
    public Course(String courseName, int courseHours, Teacher teacher) {
        this.courseName = courseName;
        this.courseHours = courseHours;
        this.teacher = teacher;
    }

3.2 Teacher里面进行添加有参构造函数

  public Teacher(){}
    public Teacher(String name, int age) {
        this.name = name;
        this.age = age;
    }

3.3 bean.xml

  <bean id="course" class="com.springdi.Course">
        <constructor-arg value="Python"></constructor-arg>
        <constructor-arg value="12"></constructor-arg>
        <constructor-arg ref="teacher"></constructor-arg>
    </bean>
    <bean id="teacher" class="com.springdi.Teacher">
        <constructor-arg value="HeloWxl"></constructor-arg>
        <constructor-arg value="20"></constructor-arg>
    </bean>

• 在bean中，<constructor-arg>的顺序要和构造方法中参数的顺序一样，即可保证第一个< constructor-arg>的value值赋值给了构造方法的第一个参数，第二个<constructor-arg>的value值赋值给了第二个参数。

如果不能保证<constructor-arg>的顺序和构造方法中参数的顺序一致，则可以使用index或者name属性指定

<!--    Index指定-->
    <bean id="course" class="com.springdi.Course">
        <constructor-arg value="java" index="0"></constructor-arg>
        <constructor-arg value="100" index="1"></constructor-arg>
        <constructor-arg ref="teacher" index="2"></constructor-arg>
    </bean>

<!--    Name指定-->
    <bean id="teacher" class="com.springdi.Teacher">
        <constructor-arg value="HeloWxl" name="name"></constructor-arg>
        <constructor-arg value="20" name="age"></constructor-arg>
    </bean>

3.4 测试方法同上

3.5 测试结果

image.png

4、命名空间方法注入

4.1bean.xml

需要在bean.xml头部引入

   xmlns:p="http://www.springframework.org/schema/p"

    <bean id="course" class="com.springdi.Course"
          p:courseHours="200"
          p:courseName=".NET"
          p:teacher-ref="teacher"
    />
    <bean id="teacher" class="com.springdi.Teacher"
          p:age="20" p:name="老王"
    />

4.2 测试方法同上

4.3 测试结果

image.png