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

This section describes Spring's beans lifecycle. It is an extract of Spring 5 training from John Tompson

Creation

This is how beans are created with Spring:

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. BeanPostProcessing : set of operations that are performed once the bean has been initalized (the Object composition is complete from Spring point of view)
   1. Pre-initialization phase: to customize the bean (and its properties) for some advanced tricks. This is usually not used at all.
   2. After properties. To get notify once the properties are set you have to implements Initializing.afterPropertiesSet()
   3. You can implement some custom loader. This is usually not used.
   4. Post-initialization phase: to customize the bean once properties are set and custom loader is complete. This is usually not used at all.
4. Bean ready to use

There is one extra step that is not on the schema:

1. Last is the Post processing: spring will run the @PostConstruct method.

Summary:

Out of the lifecyle, only the following steps are really important:

1. instanciation through the Spring bean's constructor
2. properties by setting the @Value attributes
3. bean ready to use
4. Post processing by executing the @PostConstruct

Destroy

This is how beans are destroyed with Spring:

1. Container (Tomcat, Jetty, Bash, etc.) will send the shutdown signal to the application
2. Disposable phase: Spring will call the @PreDestroy method
3. You can also specify a custom destroy method that will be call at the end by implementing DisposableBean.destroy(). This is useful for custom socket connections close (example). Ideally, on new applications you should NOT use that custom part at all.