Spring ApplicationContext Container

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The Application Context is spring's more advanced container. Similar to BeanFactory it can load bean definitions, wire beans together and dispense beans upon request. Additionally it adds more enterprise-specific functionality such as the ability to resolve textual messages from a properties file and the ability to publish application events to interested event listeners. This container is defined by the org.springframework.context.ApplicationContext interface.

The ApplicationContext includes all functionality of the BeanFactory, it is generally recommended over the BeanFactory. BeanFactory can still be used for light weight applications like mobile devices or applet based applications.

The most commonly used ApplicationContext implementations are:

  • FileSystemXmlApplicationContext: This container loads the definitions of the beans from an XML file. Here you need to provide the full path of the XML bean configuration file to the constructor.

  • ClassPathXmlApplicationContext This container loads the definitions of the beans from an XML file. Here you do not need to provide the full path of the XML file but you need to set CLASSPATH properly because this container will look bean configuration XML file in CLASSPATH.

  • WebXmlApplicationContext: This container loads the XML file with definitions of all beans from within a web application.

We already have seen an example on ClassPathXmlApplicationContext container in Spring Hello World Example, and we will talk more about XmlWebApplicationContext in a separate chapter when we will discuss web based Spring applications. So let see one example on FileSystemXmlApplicationContext.

Example:

Let us have working Eclipse IDE in place and follow the following steps to create a Spring application:

StepDescription
1Create a project with a name SpringExample and create a package com.tutorialspoint under the src folder in the created project.
2Add required Spring libraries using Add External JARs option as explained in the Spring Hello World Example chapter.
3Create Java classes HelloWorld and MainApp under the com.tutorialspoint package.
4Create Beans configuration file Beans.xml under the src folder.
5The final step is to create the content of all the Java files and Bean Configuration file and run the application as explained below.

Here is the content of HelloWorld.java file:

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);
   }
}

Following is the content of the second file MainApp.java:

package com.tutorialspoint;

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

public class MainApp {
   public static void main(String[] args) {

      ApplicationContext context = new FileSystemXmlApplicationContext
            ("C:/Users/ZARA/workspace/HelloSpring/src/Beans.xml");

      HelloWorld obj = (HelloWorld) context.getBean("helloWorld");
      obj.getMessage();
   }
}

There are following two important points to note about the main program:

  1. First step is to create factory object where we used framework API FileSystemXmlApplicationContext to create the factory bean after loading the bean configuration file from the given path. The FileSystemXmlApplicationContext() API takes care of creating and initializing all the objects ie. beans mentioned in the XML bean configuration file.

  2. Second step is used to get 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 actual object. Once you have object, you can use this object to call any class method.

Following is the content of the bean configuration file 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
    http://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>

Once you are done with creating source and bean configuration files, let us run the application. If everything is fine with your application, this will print the following message:

Your Message : Hello World!


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