IDEA: getting started with Spring: IOC inversion of control

Posted by beanman1 on Wed, 12 Feb 2020 15:11:01 +0100

1, Writing process

First create a web project using IDEA

1. Download the latest Spring development package (jar package)
2. Copy the jar package to the project project (under lib)
3. Write the core configuration file, for example (applicationContext.xml)
4. Read the Spring configuration file in the program, obtain the Bean through the Spring framework, and complete the corresponding operations

2, Import jar package

3, Write target class

1. First, create the interface and its implementation class, such as UserDao and UserDaoImpl

2. Get the instance in the UserDao implementation class

2.1 in the previous development, we just need to directly new an object. Namely: UserDao userDao = new UserDaoImpl();
2.2 after learning spring, spring will create an instance of the object – > that is, when an instance object is required after IoC inversion of control, it can be obtained from the Spring Factory (container), and the fully qualified name (path name) of the implementation class needs to be configured into the xml file

package com.chaz.dao;

public interface UserDao {
    void save();

package com.chaz.dao.impl;

import com.chaz.dao.UserDao;

 * Original coding method
public class UserDaoImpl implements UserDao {
    public void save() {
        System.out.println("The original coding method...");

4, Create and write Spring configuration file: XXX.xml

Location: any, can be leveled with src (need to be created additionally), or under src
Name: arbitrary, generally applicationContext.xml


<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns=""
    <!-- IOC Introduction to configuration 
    		<bean> Configure the objects to be created
            id : Unique, non repeatable, for subsequent Spring The
            name: It's the only one, but it's not usually used
            class : The fully qualified class name of the instance to be created -->
    <bean id="userDao" class="com.chaz.dao.impl.UserDaoImpl2"></bean>

Five. Test

package com.chaz.test;

import com.chaz.dao.UserDao;
import com.chaz.dao.impl.UserDaoImpl;
import org.junit.Test;
import org.springframework.context.ApplicationContext;

 * Test class 1
 * IOC Inversion of control
public class SpringTest {

     * Traditional writing
    public void test01(){
        UserDao userDao = new UserDaoImpl();;

     * Spring Frame writing
    public void test02(){
    	//Get container
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        //Get content from container
        UserDao bean = (UserDao) applicationContext.getBean("userDao");;

The concept of IoC (Inverse of Control) is to manually create the control right of UserDaoImpl object in the program, which is managed by Spring framework.

In short, the control to create the UserServiceImpl object is reversed to the Spring framework.
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