Hybrid Configuration Approach in Spring

Overview

• Hybrid Approach: Reduced XML, reduced Java code + majority annotations.

Steps in Spring Programming Using Annotations

1. Remove all <bean> tags from the XML configuration file.

2. Enable Annotation Support:

   • Add the context namespace and the following tag in the XML configuration:

     <context:annotation-config/>
     
     

     • Purpose: Tells Spring Container (SC) to enable class-internal annotation support (e.g., @Autowired, @PostConstruct, @PreDestroy, etc.).

   • Add the following to enable beans and context namespace:

     <beans xmlns="<http://www.springframework.org/schema/beans>"
            xmlns:xsi="<http://www.w3.org/2001/XMLSchema-instance>"
            xmlns:context="<http://www.springframework.org/schema/context>"
            xsi:schemaLocation="<http://www.springframework.org/schema/beans> <http://www.springframework.org/schema/beans/spring-beans.xsd>
                                <http://www.springframework.org/schema/context> <http://www.springframework.org/schema/context/spring-context.xsd>">
     
     

3. Specify Base Package for Spring Beans:

   • Use:

     <context:component-scan base-package="comma separated list of pkgs to specify spring beans"/>
     
     

   • Purpose: Specifies base package(s) for scanning Spring beans.

   • Behavior: SC scans the specified packages (including sub-packages) for classes annotated with stereotype annotations:

     • @Component, @Service, @Repository, @Controller, @RestController, @ControllerAdvice, etc.

Basic Class-Level Annotations for Spring Container

• Super Type:
  • @Component: Spring-managed bean class, without specific logic.
• Sub-Type Annotations:
  • @Controller: For request-handling beans in Spring Web MVC.
  • @Service: For service layer (Business Logic) beans.
  • @Repository: For DAO layer beans.
  • @RestController: For RESTful web service provider beans.
  • @ControllerAdvice: Global exception handler for all controllers.
  • @RestControllerAdvice: Global exception handler for all REST controllers.

Key Annotations and Their Usage

1. @Component:

   • Equivalent to <bean id class> in XML.

   • SC interprets it and starts the bean lifecycle.

   • Examples:

     package beans;
     @Component("abc")
     public class MyBean {...}
     
     

     • XML equivalent: <bean id="abc" class="beans.MyBean"/>

     @Component
     public class MyBean {...}
     
     

     • XML equivalent: <bean id="myBean" class="beans.MyBean"/>
2. @Controller:
   • For Spring Web MVC request-handling controllers.
3. @Repository:
   • For DAO layer classes.
4. @Service:
   • For service layer beans (Business Logic).
5. @Scope(value="singleton|prototype|request|session"):
   • Class-level annotation.
   • Equivalent to the scope attribute in XML.
6. @Lazy(true|false):
   • Class-level annotation.
   • Equivalent to the lazy-init attribute in XML.
7. @PostConstruct:
   • Method-level annotation.
   • Equivalent to the init-method attribute in XML.
8. @PreDestroy:
   • Method-level annotation.
   • Equivalent to the destroy-method attribute in XML.