Spring 5 training (Spring guru) - personal notes

I recently (2018) subscribe to an online training related to Spring 5 on Udemy. This page is a sum-up of my personal notes related to Spring 5.

Links

• Spring initializr - to generate a quick start project based on the libraries you choose

Very simple web-application

• Go to Spring initializr
• Select
  • web > web
  • SQL > JPA
  • SQL > H2
  • Templates > Thymeleaf
  • Ops > actuator

H2 hint

When using H2 on a web application, don't forget to enable the console! Edit application.properties as follow:

spring.h2.console.enabled=true
# replace "spring5webapp" by your own application
spring.datasource.url=jdbc:h2:mem:spring5webapp;DB_CLOSE_ON_EXIT=FALSE

Then you can reach the console at http://localhost:8080/h2-console

Hibernate

General notes

Hibernate recommends to implement hashCode() and equals() on all JPA entities. They also recommend to use a particular Business ID when possible, if not then use the ID. Only the key fields should be in these methods.

IntelliJ configuration

Plugins

Useful plugings:

• File > Settings > Plugins > Browse repositories
  • .ignore
  • Ideolog
  • Sonarlint
  • Save actions
  • GenerateSerialVersion

Enable toolbars! View > Toolbar

Import optimization

see https://stackoverflow.com/questions/11704327/how-to-optimize-imports-automatically-after-each-save-in-intellij-idea

IntelliJ IDEA offers 2 options:

• Settings | Editor | General | Auto Import > Optimize imports on the fly
• Commit Project dialog > Optimize imports option

Outline like Eclipse (structure view)

see https://www.jetbrains.com/help/idea/viewing-structure-of-a-source-file.html

To view the file structure, do one of the following

• On the main menu, choose View | Tool Windows | Structure.
• Pres StructureTool Button
• Press Alt+7.
• Press Ctrl+F12.

Create new Spring project

On the main menu, choose File | New | Project

• Left side: Spring initalizr (IntelliJ ultimate)

Spring 5

How to run a spring project (command line)

Spring boot provides some out-of-the-box tools.

To run the application:

# Using the maven installation (outside the project)
mvn spring-boot:run

# Using the embedded tool
./mvnw spring-boot:run

Spring MVC

Implementation of MVC concept in Spring:

Here is a short description of the schema - as I understood it + based on my experience with Spring so far (v2 to v4):

1. Client submits a request to the server (HTTP request)
2. Dispatcher receives the request
3. Dispatcher asks the Handler WHO should take care of the request? i.e:
   • What is the Controller for the requested endpoint?
   • Is there any java Method that match the given HTTP request type (GET, POST, PUT, ..) + arguments?
4. Dispatcher invokes the Controller and forwards query
   • Controller calls a Service to process the query, interact with the database and other systems.
   • Once the Service processing is complete, it returns corresponding data to the Controller
   • The Controller will convert the data into a DTO (communication Model (pojo)
   • Controller sends the pojo back to the Dispatcher
5. Data disposal: The Dispatcher disposes of the data. i.e:
   • Send back the data directly to the client [HTTP REST calls]
   • Forward the data to a View for rending
     • View generates the page thanks to UI technology (server side) such as JSP, JSF or Themeleaf to generate HTML / Javascript / CSS
     • View sends back generated content to Dispatcher
     • Dispatcher forwards content to the Client

Spring beans lifecycle

Bean lifecycle:

1. instanciation of the Class. Spring will inject dependencies through the constructor, if available.
2. populate properties. Spring will inject the @Value properties - and it will actually perform placeholder resolution against environment, properties files, profiles settings, etc.
3. Last is the Post processor: spring will run the @PostConstruct method.