Spring basic process analysis - IOC

Keywords: Java Spring

Reference video: 2021 latest Spring source code tutorial 305 episode IDEA version is easy to understand - the most complete Spring source code architect tutorial at Alibaba P8 level in station B + mybatis source code_ Beep beep beep_ bilibili

On the introduction of Spring framework, there are many good and detailed articles on the Internet. My personal ability is limited. I can only use my blog to record my current knowledge! There are mistakes, welcome to correct!

This blog will briefly introduce the simple running process of the Spring framework.

The process of SpringIOC is roughly as follows:

1. Create BeanFactory first

2. Read the information in xml into BeanDefinition through BeanDefinitionReader

3. After some processing

4. Instantiated by BeanFactory

5. Fill in attributes, such as Name and id

6. Initialization

7. Complete

Sample code

Users.java

package com.piao.pojo;

public class Users {
    private int id;
    private String name;

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

    public Users() {
    }

    public Users(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

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

}

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="user" class="com.piao.pojo.Users">
        <property name="id" value="12"/>
        <property name="name" value="mike"/>
    </bean>
</beans>

Test code

@Test
    public void test(){
        ClassPathXmlApplicationContext con = new ClassPathXmlApplicationContext("applicationContext.xml");
        Users user = con.getBean("user", Users.class);
        System.out.println(user);
    }

Process analysis

Why didn't you enter the ClassPathXmlApplicationContext class? The reasons are as follows:

Because of the inheritance relationship in the above figure, before implementing ClassPathXmlApplicationContext, the static method block identified by static in its parent class and the static attribute of initializing the parent class will be implemented first;

After that, it will enter the construction method of ClassPathXmlApplicationContext

The refresh method in the figure above is the most critical step, because many attribute initialization, BeanFactory construction and preliminary preparations are called from this method.

Back to business, let's explore it step by step,

super(parent) will call the constructor of the parent class. If there is no operation in the middle, we won't show them one by one. Go directly to

All member variables are initialized before calling the null parameter constructor.

And then

setConfigLocations(configLocations)

In fact, it can be understood as an initialization. It is understood that it is only necessary to assign values to the member variables of this class. The contents have no impact on the whole process. At the beginning, it is not necessary to study too much, otherwise it will be very confused. We have to learn to first breadth and then depth, and there is no more explanation,

And then