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Spring Boot 2 cheat sheet
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Spring Boot 2.1.x - Date : November 2018

What is Spring Boot ?

  • Built on top of a lot of Spring Projects (https://spring.io)
  • Opinionated configuration
  • Wide ecosystem
  • Start a project faster with no configuration

Features

  • Bootstrap class SpringApplication
  • Default logger (@see spring-jcl)
  • FailureAnalyzers : friendly failure report
  • Application Events on Listeners
  • Choose the right ApplicationContext
  • Accessing application arguments
  • Control application exit code

Quickstart

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.1.0.RELEASE</version>
</parent>

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

@SpringBootApplication
public class MyApp {

    public static void main(String[] args) {
        SpringApplication.run(MyApp.class, args);
    }

}

Best practices

Warning : Don't use the **default** package. Prefer using the Java convention *com.example.project*

Code structure

com
  + example
  |  + project
  |  |  - MyApp.java
  |  |  |
  |  |  + player
  |  |  |  - Player.java
  |  |  |  - PlayerService.java

Configuration

Properties files in folder src/main/resources/ are loaded automatically

  • YAML : **/application*.yml or **/application*.yaml
  • Properties : **/application*.properties

Auto-configuration

  • Enabled by @SpringBootApplication or @EnableAutoConfiguration
  • Spring Boot scans all libs on the classpath and auto-configures them (if you didn't manually)

Display Spring Boot Autoconfigure report

java -jar myapp.jar --debug

Disabling an auto-configuration class with Java conf

@EnableAutoConfiguration(exclude={DataSourceAutoConfiguration.class})

Disabling an auto-configuration class with properties

spring.autoconfigure.exclude= \
org.springframework.boot.autoconfigure.XXXX
Spring Boot 2 cheat sheet

Build a production JAR

Maven

<build>
  <plugins>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
    </plugin>
  </plugins>
</build>

Gradle

plugins {
    id 'org.springframework.boot' version '2.1.0.RELEASE'
}

Actuator

Production ready features threw HTTP or JMX

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

Running the code

Standalone

java -jar target/myapplication-0.0.1-SNAPSHOT.jar

Standalone with remote debug

java -Xdebug \
-Xrunjdwp:server=y,transport=dt_socket\
,address=8000,suspend=n -jar target/myapplication-0.0.1-SNAPSHOT.jar

Maven

mvn spring-boot:run

Gradle

gradle bootRun

Starters

Official starters : spring-boot-starter-*

Application starters

Name Function
web Web applications using Spring MVC (Tomcat embedded)
test Spring test using JUnit, Hamcrest and Mockito
security Secured services with Spring Security
webflux WebFlux applications using Spring Framework’s Reactive Web
websocket WebSocket applications using Spring Framework’s WebSocket
data-jdbc Configured resources to use Spring Data JDBC
data-mongodb Configured resources to use Spring Data JPA with Hibernate
data-rest Web applications using Spring Data repositories over REST
actuator Production ready features using Spring's Actuator (monitor and manage)

Technical starters

Name Function
jetty Using Jetty over the default Tomcat
log4j2 Using Log4j2 for logging over the default Logback
undertow Using Undertow over the default Tomcat

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