Spring - Bean Definition

The objects that form the backbone of your apppcation and that are managed by the Spring IoC container are called beans. A bean is an object that is instantiated, assembled, and otherwise managed by a Spring IoC container. These beans are created with the configuration metadata that you supply to the container. For example, in the form of XML <bean/> definitions which you have already seen in the previous chapters.

Bean definition contains the information called configuration metadata, which is needed for the container to know the following −

How to create a bean

Bean s pfecycle details

Bean s dependencies

All the above configuration metadata translates into a set of the following properties that make up each bean definition.

Spring Configuration Metadata

Spring IoC container is totally decoupled from the format in which this configuration metadata is actually written. Following are the three important methods to provide configuration metadata to the Spring Container −

XML based configuration file.

Annotation-based configuration

Java-based configuration

You already have seen how XML-based configuration metadata is provided to the container, but let us see another sample of XML-based configuration file with different bean definitions including lazy initiapzation, initiapzation method, and destruction method −

<?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">

   <!-- A simple bean definition -->
   <bean id = "..." class = "...">
      <!-- collaborators and configuration for this bean go here -->
   </bean>

   <!-- A bean definition with lazy init set on -->
   <bean id = "..." class = "..." lazy-init = "true">
      <!-- collaborators and configuration for this bean go here -->
   </bean>

   <!-- A bean definition with initiapzation method -->
   <bean id = "..." class = "..." init-method = "...">
      <!-- collaborators and configuration for this bean go here -->
   </bean>

   <!-- A bean definition with destruction method -->
   <bean id = "..." class = "..." destroy-method = "...">
      <!-- collaborators and configuration for this bean go here -->
   </bean>

   <!-- more bean definitions go here -->
   
</beans>

You can check Spring Hello World Example to understand how to define, configure and create Spring Beans.

We will discuss about Annotation Based Configuration in a separate chapter. It is intentionally discussed in a separate chapter as we want you to grasp a few other important Spring concepts, before you start programming with Spring Dependency Injection with Annotations.