What is Spring Bean? What is Spring Container? IoC (inversion of control) | Creating a simple Spring project and configuration Spring Container in an XML file

Programming, development, testing

→

Java

→

Spring in Java (Spring Framework, Spring Data, Spring Boot, ...)

→

What is Spring Bean? What is Spring Container? IoC (inversion of control) | Creating a simple Spring project and configuration Spring Container in an XML file | Editor IntelliJ Idea and language Java

Looked at 2904 times Comments 5

Last Comment: (4 February 2025 10:38) Спасибо, вы правы есть ошибка в [java_code]Book book =... read... Write a comment...

What is Spring Bean, Spring Container? IoC (inversion of control) | Creating a simple Spring project and configuration Spring Container in an XML file | Editor IntelliJ Idea and language Java

last updated: 7 April 2025

I create a regular object like this:

Java

Book book = new Book();

What is Spring Bean?

Spring Bean This is a regular object that is not created by me, but the object is created by Spring Container.

Java

Spring Container knows how to create my object(Bean) because everything is described in the configuration file:

<?xml version="1.0" encoding="UTF-8"?>
<beans>

<bean id="myBook1" class="com.example.springproj1.Book">
</bean>

</beans>

Note! Why use Spring to create an object when you can create my object in one line:
Book book = new Book();
Answer: Because it's a good style to describe all objects in a single configuration file xml.

What is Spring Container?

Spring Container is responsible for creating Bean (my object).

Spring Container performs 2 functions: IoC and DI

IoC - inversion of control (you do not create and manage objects, the library Spring creates and manages objects itself)

Interface org.springframework.context.ApplicationContext represents IoC Spring Container and is responsible for creating, configuring Bean because it inherits from interface BeanFactory.
ApplicationContext (IoC Spring Container) knows how to create objects, but needs to be configured.

You can make a configuration for IoC Spring Container using:
1) XML file (I use it in my example below)
    The ClassPathXmlApplicationContext class is an implementation of the ApplicationContext interface.
    The ClassPathXmlApplicationContext class takes the configuration from the XML file.

  2) Annotations in Java: @Service, @Component, @Scope

3) Java code: @Configuration, @ComponentScan, @Bean
@Configuration indicate configuration class.
@Bean indicate method that create bean.

Configuration for IoC Spring Container is an explanation for IoC Spring Container how to create bean objects.
Someone who controls and can manage all of your classes is called ApplicationContext (IoC Spring Container)

DI - Dependency Injection (used to create complex objects)

Note! In my example below, I don't use Dependency Injection. Because I have only one class in my example.
And for Dependency Injection you need two classes that depend on each other

DI Spring is when a class needs another class...

Create a simple Spring project and configure Spring Bean in an XML file | Editor IntelliJ Idea and language Java

Download an example:

SpringProj1.zip ...
size: 20 kb

Note! You must have Java JDK installed. If you don't have it, then need to download and install Java JDK ...

Note! You must have IntelliJ IDEA Ultimate installed. If you don't have it, then need to download and install IntelliJ IDEA ...

Step 1. Create a new project with the type Spring Boot

Select Spring Boots:

Since we have a simple project, do not check the boxes:

The project was created:

Step 2. Create a new Book.java file

Right-click on my package folder and create a new java file

Let's write the name Book
And choose the type Class

Press Enter
The file was created.

Inside the Book.java file, add the code:

package com.example.springproj1;

public class Book {
     public String name;

     public Book()
     {
          name = "Tom Sawyer";
     }
}

Step 3. Create a new configuration MyConfig.xml file

Right-click on the folder resources and create a new Spring Config file

Let's write the name MyConfig

Press Enter
The file was created.

Inside the MyConfig.xml file, add bean a description:
Spring reads the bean description from the xml file and knows how to create the bean object in the future.

<?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="myBook1" class="com.example.springproj1.Book">
     </bean>

</beans>

Step 4. Add the code to the SpringProj1Application.java file

// Spring Container creates bean.
ApplicationContext context = new ClassPathXmlApplicationContext("MyConfig.xml"); // Create Spring Container from the configuration file
Book book = (Book) context.getBean("myBook1"); // Spring Container creates a book object by id

// Showing the result on the screen
System.out.println("See what book created: " + book.name); // Displaying the name of the book

Note!

// Option 1
Book book = (Book) context.getBean("myBook1");

// Or you can do it like this

// Option 2
Book book = context.getBean("myBook1", Book.class);

Step 5. Launching the project

To start the project, you need to open the application java file and click on the green triangle:

After launching the program, we will see the result on the screen:

See what book created: Tom Sawyer

← Previous topic
What is Spring? Why use Spring in Java?

Next topic →
What is Dependency Injection in Spring? Creating a simple Spring project with Dependency Injection in the constructor with the attributes @Component, @Autowired | Editor IntelliJ Idea and language Java