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[Theory+Example] Spring Boot Command Line Runner

If you need to run some specific code once the SpringApplication has started, you can implement the ApplicationRunner or CommandLineRunner interfaces. Both interfaces work in the same way and offer a single run method which will be called just before SpringApplication.run(…​) completes.

 

The CommandLineRunner interfaces provides access to application arguments as a simple string array, whereas the ApplicationRunner uses the ApplicationArguments interface.

 

Logging with Spring Boot

Spring Boot has no mandatory logging dependency, except for the Commons Logging API, of which there are many implementations to choose from.

Spring Boot attempts to configure logging based on the content of the classpath if you use spring-boot-starter-logging. Other starters such as spring-boot-starter-web depends transitively on the logging starter, and hence it is automatically added if they are being used.

 

Spring Boot Dependency Management - BOM and Uber Jar

Bill of Materials

Spring boot calls its collection of dependencies as BOM or bill of materials.

The Spring Boot starter parent is responsible for most of the default configurations, plugins etc. which aides in the BOM. When adding dependencies, Spring boot tries to add matching dependency versions which will work together well.  Your starter dependencies such as spring-boot-starter-web will not have to specify any versions.

[Example] A Simple Spring Boot REST Web Application

A Spring Boot application uses the @SpringBootApplication annotation over the main executable class. The SpringApplication.run method call accepts two parameters — the configuration class annotated with @SpringBootApplication annotation and any application arguments. 

 

Bean Components

We will use a simple bean class based on our previous examples. 

Introduction to Spring Boot

Spring Boot can help us create Spring applications much faster than otherwise. Spring Boot is based on "conventions over configuration" and you have to do very little in configuring an application. For example, you can create a web application with an embedded server in few minutes and you can "just run" them like a desktop application. 

Spring boot home page @ https://projects.spring.io/spring-boot/ describe itself as follows:

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