Spring基于XML的DI之构造注入

蔚落 2023-10-17 12:04 1阅读 0赞

## Spring基于XML的DI之构造注入 ##

#### 构造注入       ####

##### 构造注入是指，在构造 调用者实例化的同时，完成被调用者的实例的初始化，即：使用构造器设置依赖关系。       #####

#### 举个栗子       ####

#### Studnet.java ####

package com.hk.spring.di02;
    
    public class Student {
    
        private String name;
        private int age;
        private School school;//域属性
    
        public Student() {
            System.out.println("无参构造器被执行");
        }
    
        public Student(String name, int age, School school) {
            this.name = name;
            this.age = age;
            this.school = school;
        }
        public void setSchool(School school) {
            this.school = school;
        }
        @Override
        public String toString() {
            return "Student [name=" + name + ", age=" + age + ", school=" + school
                    + "]";
        }
    
    
    }

#### School.java ####

package com.hk.spring.di02;
    
    public class School {
        
    
        private String schloolName;
    
        public void setSchloolName(String schloolName) {
            this.schloolName = schloolName;
        }
    
        @Override
        public String toString() {
            return "School [schloolName=" + schloolName + "]";
        }
    
    }

#### applicationContext.xml ####

<?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.xsd">
        
        <bean id="mySchool" class="com.hk.spring.di02.School">
            <property name="schloolName" value="红林小学"/>
        </bean>
        <bean id="myStudent" class="com.hk.spring.di02.Student">
            
            <constructor-arg index="0" value="小明"/>
            <constructor-arg index="1" value="9"/>
            
            <constructor-arg index="2" ref="mySchool"/>
        </bean>
    </beans>

##### 又是似曾相识的index，这玩意先别说不一定知道从0还是1开始，光是顺序就要搞死人，所以一般用name属性       #####

#### applicationContext.xml优化版 ####

<?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.xsd">
        
        <bean id="mySchool" class="com.hk.spring.di02.School">
            <property name="schloolName" value="红林小学"/>
        </bean>
        <bean id="myStudent" class="com.hk.spring.di02.Student">
            
            <constructor-arg name="name" value="小明"/>
            <constructor-arg name="age" value="9"/>
            
            <constructor-arg name="school" ref="mySchool"/>
        </bean>
    </beans>

#### 测试类 ####

package com.hk.spring.di02;
    
    import org.junit.Test;
    import org.springframework.context.ApplicationContext;
    import org.springframework.context.support.ClassPathXmlApplicationContext;
    
    public class Mytest {
        @Test
        public void test1(){
            String resource = "com/hk/spring/di02/applicationContext.xml";
            ApplicationContext ac = new ClassPathXmlApplicationContext(resource);
            Student stu = (Student) ac.getBean("myStudent");
            System.out.println(stu);
    
        }
    }

#### 结果 ####

Student [name=小明, age=9, school=School [schloolName=红林小学]]

##### 可能你已经发现了，无参构造器并没有执行，其实构造注入不需      要无参构造器，但是无参构造器还是需要的，别的地方可能会使用 #####