Spring Concepts Overview

1. Revise Spring Bean Lifecycle

• Reference: "Spring Reference Material\diagrams\spring-bean-life-cycle.png"
• Note: The Spring bean lifecycle includes stages such as:
  • Instantiation
  • Dependency injection
  • Initialization (@PostConstruct or init-method)
  • Usage
  • Destruction (@PreDestroy or destroy-method)
  • Managed by the Spring Container (SC).

2. Different Modes of Wiring in Spring

• Reference: "Spring Reference Material\diagrams\spring wiring.png"
• Modes:
  • Explicit Wiring:
    • Constructor-based DI
    • Setter-based DI
    • Factory method-based DI
  • Implicit Wiring (Autowiring):
    • byName
    • byType
    • constructor

3. Continue to Autowiring

• Field-Level Dependency Injection (DI) (No setters, no parameterized constructor):

  1. @Autowired:

     // => autowire="byType"
     private Teacher myTeacher;
     
     

     • Outcomes:
       • No Match: SC throws NoSuchBeanDefinitionException.
       • Multiple Matches: SC throws NoUniqueBeanDefinitionException.
       • Exact Match: No exceptions, business logic (B.L) works using dependencies.

  2. @Autowired(required=false):

     // => autowire="byType"
     private Teacher myTeacher;
     
     

     • Outcomes:
       • No Match: Business logic failure (e.g., NullPointerException).
       • Multiple Matches: SC throws NoUniqueBeanDefinitionException.
       • Exact Match: No exceptions, B.L works using dependencies.

  3. @Autowired with @Qualifier:

     // => autowire="byType"
     @Qualifier("eng") // => byName
     private Teacher myTeacher;
     
     

     • Outcomes:
       • No Match: SC throws NoSuchBeanDefinitionException.
       • Multiple Matches: SC throws NoUniqueBeanDefinitionException.
       • Exact Match: No exceptions, B.L works using dependencies.

4. Hybrid Approach (Lesser XML, Majority Annotations)

• References:
  • "day12-data\day12_help\spring sequence for annotations.txt"
  • "Spring Reference Material\diagrams\xml vs annotations.png"
• Steps:

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

  2. Enable Annotation Support:

     • Add context namespace and the following tag:

       <context:annotation-config/>
       
       

       • Purpose: Enables class-internal annotations (e.g., @Autowired, @PostConstruct, @PreDestroy).

     • Include namespace configuration:

       <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 Component Scanning:

     • Use:

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

     • SC scans specified packages (and sub-packages) for classes annotated with stereotype annotations (@Component, @Service, @Repository, @Controller, @RestController, @ControllerAdvice).

• Stereotype Annotations:
  • @Component: Generic Spring-managed bean.
  • @Controller: Request-handling bean for Spring Web MVC.
  • @Service: Service layer (Business Logic) bean.
  • @Repository: DAO layer bean.
  • @RestController: RESTful web service provider bean.
  • @ControllerAdvice: Global exception handler for controllers.
  • @RestControllerAdvice: Global exception handler for REST controllers.

5. Enter Spring MVC

• Reference: "day12-data\day12_help\Spring MVC\steps for spring mvc.txt"
• End Objective: CRUD with restaurants
• Objectives:
  1. Test Spring MVC flow.
  2. Test ModelAndView to generate dynamic responses.

MVC in Custom Implementation

• Model: Java Bean (conversational state holder + B.L supplier) & POJOs.