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.
Contents
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
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)
HTTP protocol
Just some quick summary related to HTTP protocol and HTTP requests:
Spring 5
Spring properties
You can find the properties hierarchy over here: https://docs.spring.io/spring-boot/docs/current/reference/html/boot-features-external-config.html
command line tricks
Spring boot provides some out-of-the-box tools.
Run the application
To run the application:
# Using the maven installation (outside the project)
mvn spring-boot:run
# Using the embedded tool
./mvnw spring-boot:run
See spring-boot commands
mvn spring-boot:help -Ddetail=true
See all spring boot magic
To see all the magic you can start in FULL DEBUG mode. This is more than the "DEBUG" logs! This will:
- Load the application
- Display each spring action such as component scan, auto-configuration, properties load, ignore beans and configuration
- Give additional information regarding spring beans access and catalog update
- etc.
mvn spring-boot:run -Dspring-boot.run.arguments=--debug
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):
- Client submits a request to the server (HTTP request)
- Dispatcher receives the request
- 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?
- 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
- 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. This is a summary of lecture 37.
Creation
This is how beans are created with Spring:
Complete description
This is the complete description of the creation lifecyle:
- instantiation of the Class. Spring will inject dependencies through the constructor, if available.
- populate properties. Spring will set the @Value attributes: it will perform placeholder resolution against environment, properties files, profiles settings, etc.
- BeanPostProcessing : set of operations that are performed once the bean has been initialized (the Object composition is complete). You just have to implements the
BeanPostProcessort
interface. These features are usually NOT used.- Pre-initialization phase: to customize the bean (and its properties) for some advanced tricks.
- After properties. To get notify once the properties are set. You have to implements
Initializing.afterPropertiesSet()
interface. - You can implement some custom loader.
- Post-initialization phase: to customize the bean once properties are set and custom loader is complete.
- Bean ready to use
There is one extra step that is not on the schema: Post processing. Spring will run the @PostConstruct
method.
Simplify lifecycle
Some steps of the lifecycle are mostly dedicated to the Spring creators and related frameworks.
Most of the Spring users only use:
- instantiation through the Spring bean's constructor
- properties by setting the @Value attributes
- Bean ready to use
- Post processing by executing the
@PostConstruct
Awareness
In the 'initialization' phase - as well as the 'reload' phase - you might want to listen to events that occurs within the application and have impact on the Spring context. Here is a list of the most common aware interfaces:
In all honesty, I've only worked with the ApplicationContextAware
interface in 7 years of Spring.
Destroy
This is how beans are destroyed with Spring:
- Container (Tomcat, Jetty, Bash, etc.) will send the shutdown signal to the application
- Disposable phase: Spring will call the @PreDestroy method
- 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.
Spring bean components
Hierarchy
You'll find below the Spring beans components hierarchy:
Each type @Controller, @Service, @Repository provides additional @nnotations + they are marked to belong to a particular N-third layer. This helps Spring a lot.