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Spring Boot Fundamentals

Overview:

  • Features of Spring Boot
    • Spring Boot starters
    • Auto configuration
  • Bootstrapping an application
    • Spring Initializr
  • Data access
  • Spring MVC

Starter Dependency

Spring Boot requires only one dependency to get all the basics for web application development up and running:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

Includes:

  • Spring MVC
  • REST
  • Tomcat
  • Jackson

Spring boot will add most of the libraries needed for testing using also just one dependency:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-test</artifactId>
  <scope>test</scope>
</dependency>

Includes:

  • JUnit
  • Mockito
  • Hamcrest
  • Spring Core
  • Spring Test

Another dependency will add everything required for Spring Data JPA with Hibernate:

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>

Includes:

  • Hibernate
  • Spring Data JPA
  • Spring ORM

Spring Boot CLI

  • Command Line Interface
  • Applications using Groovy scripts
  • Rapid Prototyping

Installation

Linux:

curl -s "https://get.sdkman.io" | bash

sdk install springboot

spring --version

Windows:

  • Go to this link
  • Download and extract spring-boot-cli-2.5.4-bin.zip to a desired location
  • Follow the 'INSTALL.txt'-instructions
    • Create a SPRING_HOME environment variable
    • Add %SPRING_HOME%/bin to the classpath
    • (Or just use the 'spring.bat'-file in the bin folder)

Generating Projects

spring init fundamentals2

spring init --dependencies=web,data-jpa fundamentals3

Running Groovy Scripts

spring run app.groovy

Actuator

  • Monitor running application
  • Manage via HTTP endpoints or JMX
  • Health status, metrics, loggers, audit events, HTTP trace

Bill of Materials (BOM)

The parent pom.xml holds pre-configured versions for a lot of dependencies, selected by the Spring team to work well together:

<parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.4</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

Auto-Configuration

Spring Boot takes a convention over configuration approach.

  • Finds JARs on the classpath and auto-configures bean
  • DAta source for Hibernate or DispatcherServlet for Spring MVC
  • User defined beans take precedence over defaults
  • Auto-configuration is applied after user defined beans are registered

Insights:

  • Start application with --debug switch

  • Add a simple property to application.properties

    logging.level.org.springframework=DEBUG

  • Use the Spring Boot Actuator

Annotations

The @SpringBootApplication annotation:

  • @SpringBootConfiguration

    Replaces @Configuration and annotates a class af configuration

  • @EnableAutoConfiguration

    Tells Spring Boot to configure beans

  • @ComponentScan

    Tells Spring Boot to scan current package and subpackages

Properties

Common Application Properties

Different properties for multiple Spring Boot Profiles:

applications-{profile}.properties

ORM with JPA

  • Persistence Data Store

  • Java Database Connectivity (JDBC)

    Connects to DB and executes queries

  • Java Persistence API (JPA)

    Abstraction that makes it easy to map Java objects to relational DB (Doesn't 'DO' anything)

  • Hibernate (Persistence Provider, Springs implementation for JPA)

    Provides repository support for the JPA

MVC

  • Model

    Representation of data in te system

  • View

    Responsible for displaying data

  • Controller

    Directing incoming user requests

Thymeleaf

  • Fragments
  • Repeatable chunks of code
  • Components reused across pages

Spring Boot Maven Plugin

  • Repackages our JAR / WAR files to be executed
  • Runs Spring Boot Application
  • Provides built-in dependency resolver
  • Manages lifecycle of Spring Boot Application

Packaging & Deployment

Options:

  • Packaged as a traditional web application in a WAR file
  • Standalone application, packaged in executable JAR file