Spring notes 6-value and the difference between ref

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Considering the complete type of learning knowledge, I think it is necessary to take out the difference between value and ref and talk about it separately, but to be honest, this thing is still very easy to distinguish, and it is very fast to learn!

The difference is briefly described above

value: when the object of the bean instance injects the object property through the setter method, the property does not belong to the bean-id reference
ref: when the object of the bean instance injects the object property through the setter method, the property belongs to the bean-id Reference (usually only when the type is injected into the attribute of the class)

Look at the following example to understand the description, and get ready for the pre-work
1. Create a template (any name)

2. Create beans.xml file under resource

3. Create a package on blue java, create User class and Friend class under the package

4. Create myTest class on green java and

import basic configuration information in beans.xml

Code:

<?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
       https://www.springframework.org/schema/beans/spring-beans.xsd">

</beans>

Write the following attributes in the User class

Code:

public class User {
    
    
    private Friend myFriend;
    private String name;

    public Friend getMyFriend() {
    
    
        return myFriend;
    }

    public void setMyFriend(Friend myFriend) {
    
    
        this.myFriend = myFriend;
    }

    public String getName() {
    
    
        return name;
    }

    public void setName(String name) {
    
    
        this.name = name;
    }

    @Override
    public String toString() {
    
    
        return "User{" +
                "myFriend=" + myFriend.toString() +
                ", name='" + name + '\'' +
                '}';
    }
}

Write the following properties under the Friend class

Code:

package com.ysj.study;

public class Friend {
    
    
    private String name;
    private int age;

    public String getName() {
    
    
        return name;
    }

    public void setName(String name) {
    
    
        this.name = name;
    }

    public int getAge() {
    
    
        return age;
    }

    public void setAge(int age) {
    
    
        this.age = age;
    }

    @Override
    public String toString() {
    
    
        return "Friend{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

I believe students who have learned this should know that if you instantiate an object through the id of the bean.

First of all, for the int and String properties, they can be injected directly, without instantiation, so you can inject the value through the value.
But for the myFriend property, it is an object, and the instantiation of the class must be handed over to the bean for assembly and instantiation. One of the bean-id in this figure is an object of the Freind class, called friend. So you can inject this value into the id object of myUser, but because friend is assembled in a bean, you cannot use value. To use ref (reference bean-id),
in fact, to summarize ,As long as the value you need to inject is bean-id, use ref, otherwise you can use value (in the case of some complex types that are not considered)

Write the following code under the myTest class

Code:

import com.ysj.study.User;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class myTest {
    
    
    public static void main(String[] args) {
    
    
        ApplicationContext context = new ClassPathXmlApplicationContext("beans.xml");

        User myUser = (User) context.getBean("myUser");

        System.out.println(myUser.toString());
    }
}

Output result