Spring Tutorial for Beginners

Introduction
Spring Framework
Create Maven Project
Declaring basic library of Spring
Code Project
Spring @Configuration & IoC
Spring ApplicationContext
Working Principle of Spring
Programming Web Application using Spring Boot
Appendix: Download Spring Library

1. Introduction

This document is written based on:

Spring Framework 4.x
Eclipse 4.6 NEON (ok for Eclipse 4.5 MARS)

In this document, I use Maven to declare the Spring library will use, instead of downloading Spring library and declaring in the normal way.

Maven is a tool that help you manage your library automatically and efficiently, and it has become customary which any Java programmers must know. If you do not know about Maven you can spend 10 minutes to learn how to use it here:

Maven Tutorial for Beginners

In case you want to download Spring and declare the library in the traditional way you can see the appendix at the end of the document.

2. Spring Framework

The illustration below shows the structure of the Spring Framework.

IoC Container: This is the most important and also the basis, the foundation of Spring. It is the role of configuration and lifecycle management of Java objects. Posts Today we will learn about this part.
DAO, ORM, AOP, WEB: The module is available tool or framework is integrated into the Spring.

Inversion of Control & Dependency Injection

To understand this issue we take a few classes below:

// Interface HelloWorld
public interface HelloWorld {
    public void sayHello();
}

// Class implements HelloWorld
public class SpringHelloWorld implements HelloWorld {
   public void sayHello()  {
           System.out.println("Spring say Hello!");
   }
}

// Other class implements HelloWorld
public class StrutsHelloWorld implements HelloWorld {
   public void sayHello()  {
           System.out.println("Struts say Hello!");
   }
}


// And Service class
public class HelloWorldService {
   
     // Field type HelloWorld
     private HelloWorld helloWorld;
   
     // Constructor HelloWorldService
     // It initializes the values for the field 'helloWorld'
     public HelloWorldService()  {
           this.helloWorld = new StrutsHelloWorld();
     }

}

It is obvious that class HelloWorldService manages the creation of HelloWorld objects.

- In the above situation, when a HelloWorldService object is created from its constructor, HelloWorld object is also created. It is created from StrutsHelloWorld.

The question is that you want to create a HelloWorldService object and HelloWorld object is simultaneously created, but it has to be SpringHelloWorld.
So HelloWorldService is controlling "object creation" of HelloWorld. Why don't we transfer the creation of HelloWorld to a third party, instead of making it in HelloWorldService? We have the definition of "inversion of control" (IoC).

And IoC Container will act as manager and creating both HelloWorldService and HelloWorld.

IoC = Inversion of Control

IoC container creates HelloWorldService object and then pass the object HelloWorld into HelloWorldService through setter. The IoC container is doing is "dependency injection" into HelloWorldService. The dependence here means that the dependence between objects: HelloWorldService and HelloWorld.

At this point we have identified clearly what IoC & DI. Let's take an example to better understand.

3. Create Maven Project

File/New/Other...

Enter:

Group Id: org.o7planning
Artifact Id: HelloSpringAnnotation
package: org.o7planning.spring

Your project has been created:

Ensure that your Project is built on Java 7 or newer. Right-click the project and select Properties.

4. Declaring basic library of Spring

This is HelloWorld Spring example, so we just use the basic Spring library (Core). Open the pom.xml file to declare the library will use:

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/POM/4.0.0
  http://maven.apache.org/xsd/maven-4.0.0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.o7planning</groupId>
  <artifactId>HelloSpringAnnotation</artifactId>
  <version>0.0.1-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>HelloSpringAnnotation</name>
  <url>http://maven.apache.org</url>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

    <dependencies>

        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>3.8.1</version>
            <scope>test</scope>
        </dependency>

        <!-- Spring Core -->
        <!-- http://mvnrepository.com/artifact/org.springframework/spring-core -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>4.1.4.RELEASE</version>
        </dependency>

        <!-- Spring Context -->
        <!-- http://mvnrepository.com/artifact/org.springframework/spring-context -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context</artifactId>
            <version>4.1.4.RELEASE</version>
        </dependency>

    </dependencies>
 
</project>

5. Code Project

Below is an illustration of the project structure:

Language.java

package org.o7planning.spring.lang;

// A Language
public interface Language {

    // Get a greeting
    public String getGreeting();

    // Get a bye
    public String getBye();

}

English.java

package org.o7planning.spring.lang.impl;

import org.o7planning.spring.lang.Language;

// English
public class English  implements Language {

 @Override
 public String getGreeting() {
     return "Hello";
 }

 @Override
 public String getBye() {
     return "Bye bye";
 }


}

Vietnamese.java

package org.o7planning.spring.lang.impl;

import org.o7planning.spring.lang.Language;

// Vietnamese
public class Vietnamese implements Language {

   @Override
   public String getGreeting() {
       return "Xin Chao";
   }

   @Override
   public String getBye() {
       return "Tam Biet";
   }

}

@Service is an annotation which is used to annotate on a class to inform Spring that the class is a Spring BEAN.

@Autowired is annotated on a field to inform Spring that let's inject value into the field. Note: The meaning of term "inject" is similar to assigning a value to that field.

GreetingService.java

package org.o7planning.spring.bean;

import org.o7planning.spring.lang.Language;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class GreetingService {

   @Autowired
   private Language language;

   public GreetingService() {

   }

   public void sayGreeting() {
       
       String greeting = language.getGreeting();

       System.out.println("Greeting: " + greeting);
   }

}

@Repository is an annotation which is used to annotate on a class to inform Spring that the class is a Spring BEAN.

MyRepository.java

package org.o7planning.spring.bean;

import java.util.Date;

import org.springframework.stereotype.Repository;

@Repository
public class MyRepository {

    public String getAppName() {
        return "Hello Spring App";
    }

    public Date getSystemDateTime() {
        return new Date();
    }
    
    
}

@Component is an annotation which is used to annotate on a class to inform Spring that the class is a Spring BEAN.

@Autowired is annotated on a field to inform Spring that let's inject value into the field. Note: The meaning of term "inject" is similar to assigning a value to that field.

MyComponent

package org.o7planning.spring.bean;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class MyComponent {
   
    @Autowired
    private MyRepository repository;

    public void showAppInfo() {
        System.out.println("Now is: "+ repository.getSystemDateTime());
        System.out.println("App Name: "+ repository.getAppName());
    }

}

There is no difference between the usage of @Service, @Component and @Repository, you can use them to annotate on your class that is suitable for the meaning and context of the application.

6. Spring @Configuration & IoC

@Configuration is an annotation which is annotated in a class defining Spring BEANs.

@ComponentScan - Deliver report to Spring about packages to search for other Spring BEANs, Spring will scan the packages to search for.

AppConfiguration.java

package org.o7planning.spring.config;

import org.o7planning.spring.lang.Language;
import org.o7planning.spring.lang.impl.Vietnamese;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

@Configuration
@ComponentScan({"org.o7planning.spring.bean"})
public class AppConfiguration {

    @Bean(name ="language")
    public Language getLanguage() {

        return new Vietnamese();
    }
     
}

Spring BEANs that are created will be managed in Spring IoC Container.

7. Spring ApplicationContext

MainProgram.java

package org.o7planning.spring;

import org.o7planning.spring.bean.GreetingService;
import org.o7planning.spring.bean.MyComponent;
import org.o7planning.spring.config.AppConfiguration;
import org.o7planning.spring.lang.Language;
import org.springframework.context.ApplicationContext;
import org.springframework.context.annotation.AnnotationConfigApplicationContext;

public class MainProgram {

   public static void main(String[] args) {

       // Creating a Context Application object by reading
       // the configuration of the 'AppConfiguration' class.
       ApplicationContext context = new AnnotationConfigApplicationContext(AppConfiguration.class);

       System.out.println("----------");
       Language language = (Language) context.getBean("language");
     
       System.out.println("Bean Language: "+ language);
       System.out.println("Call language.sayBye(): "+ language.getBye());
     
       System.out.println("----------");
     
       GreetingService service = (GreetingService) context.getBean("greetingService");
 

       service.sayGreeting();
 
       System.out.println("----------");
     
       MyComponent myComponent = (MyComponent) context.getBean("myComponent");
     
       myComponent.showAppInfo();
     
   }
 
}

Run MainProgram class

Results:

8. Working Principle of Spring

You create an ApplicationContext object by reading configures in class AppConfiguration. For example, see the code below.

ApplicationContext context = new AnnotationConfigApplicationContext(AppConfiguration.class);

Spring will create Spring BEANs according to the definitions in class AppConfiguration (Note: AppConfiguration class must be annotated by @Configuration).

Next, Spring will search in package "org.o7planning.spring.bean" in order to create other Spring BEANs (Create objects from classes annotated by @Service, @Component or @Repository).

Spring BEAN is now created and is contained in Spring IoC. The fields of Spring BEANs are annotated by @Autowired that will have values injected. Let's see illustration below:

So, what is IoC?
In case that an object is created from a class traditionally, its fields have value assigned inside the class. Reversely, for Spring, its objects and fields have value injected from the outside by an object called as IoC.

IoC stands for "Inversion of Control"

IoC Container is a container containing all Spring BEANs used in the application.

9. Programming Web Application using Spring Boot

Next you can learn programming web applications with Spring Boot:

Spring Boot Tutorial for Beginners

10. Appendix: Download Spring Library

You can download Spring at:

https://maven.springframework.org/release/org/springframework/spring/

Unzip the downloaded zip file to a hard drive folder: