Spring - Hello World Example

Let us start actual programming with Spring Framework. Before you start writing your first example using Spring framework, you have to make sure that you have set up your Spring environment properly and created a project as explained in Spring - Environment Setup Chapter. We also assume that you have a bit of working knowledge on Eclipse IDE.

Now let us proceed to update the simple Spring Application, which will print "Hello World!" or any other message based on the configuration done in Spring Beans Configuration file.

Create Source Files

Now let us create actual source files under the spring project. First we need to create a package called com.tutorialspoint. To do this, right click on src in package explorer section and follow the option − New → Package.

Next we will create HelloWorld.java and MainApp.java files under the com.tutorialspoint package.

HelloWorld.java

package com.tutorialspoint;

public class HelloWorld {
   private String message;

   public void setMessage(String message){
      this.message  = message;
   }
   public void getMessage(){
      System.out.println("Your Message : " + message);
   }
}

MainApp.java

package com.tutorialspoint;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class MainApp {
   public static void main(String[] args) {
      ApplicationContext context = new ClassPathXmlApplicationContext("Beans.xml");
      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();
   }
}

Following two important points are to be noted about the main program −

• The first step is to create an application context where we used framework API ClassPathXmlApplicationContext(). This API loads beans configuration file and eventually based on the provided API, it takes care of creating and initializing all the objects, i.e. beans mentioned in the configuration file.

• The second step is used to get the required bean using getBean() method of the created context. This method uses bean ID to return a generic object, which finally can be casted to the actual object. Once you have an object, you can use this object to call any class method.

Create Bean Configuration File

You need to create a Bean Configuration file which is an XML file and acts as a cement that glues the beans, i.e. the classes together. This file needs to be created under the src/main/resources directory of maven project to ensure file is in classpath.

Usually developers name this file as Beans.xml, but you are independent to choose any name you like. You have to make sure that this file is available in CLASSPATH and use the same name in the main application while creating an application context as shown in MainApp.java file.

The Beans.xml is used to assign unique IDs to different beans and to control the creation of objects with different values without impacting any of the Spring source files. For example, using the following file you can pass any value for "message" variable and you can print different values of message without impacting HelloWorld.java and MainApp.java files. Let us see how it works −

Beans.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%20%20%20http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">

   <bean id = "helloWorld" class = "com.tutorialspoint.HelloWorld">
      <property name = "message" value = "Hello World!"/>
   </bean>

</beans>

When Spring application gets loaded into the memory, Framework makes use of the above configuration file to create all the beans defined and assigns them a unique ID as defined in <bean> tag. You can use <property> tag to pass the values of different variables used at the time of object creation.

Running the Program

Once you are done with creating the source and beans configuration files, you are ready for this step, which is compiling and running your program. To do this, keep MainApp.Java file tab active and use either Run option available in the Eclipse IDE or use Ctrl + F11 to compile and run your MainApp application. If everything is fine with your application, this will print the following message in Eclipse IDE's console −

Your Message : Hello World!

Congratulations, you have successfully created your first Spring Application. You can see the flexibility of the above Spring application by changing the value of "message" property and keeping both the source files unchanged.