Build Tools and Project Setup

7 pages · ~5 min✓ Reviewed

Start here. Next up: Core: IoC and Dependency Injection.

Spring BootPage 1

Spring Initializr and the Boot Mental Model

1. What Boot Is

Boot = Spring + auto-configuration + starters + embedded server
Beans are configured from the classpath: almost no XML or boilerplate
Initializr generates a zipped skeleton: build file, main class, test class
Also in the zip: application.properties, wrapper scripts
Reach it at start.spring.io, an IDE wizard, or curl

2. Initializr Choices

Choice	Options
Project type	Maven or Gradle
Language	Java, Kotlin, Groovy
Boot version	pick a stable release
Group / artifact	project coordinates
Packaging	jar or war
Java version	e.g. 21
Dependencies	starters like `web`, `data-jpa`

The same choices work from the command line via -d flags

bash

curl https://start.spring.io/starter.zip \
  -d dependencies=web,data-jpa \
  -d type=maven-project \
  -d javaVersion=21 \
  -o demo.zip

downloads demo.zip, a ready Maven project

3. Convention over Configuration

Default	Value
Port	8080
Server	embedded Tomcat
Config file	`application.properties`

Override only when needed

Boot ships sensible defaults. Change a setting only when the default does not fit.

Spring BootPage 2

Maven vs Gradle

1. Two Build Tools

	Maven	Gradle
Config	XML `pom.xml`	Groovy / Kotlin DSL `build.gradle(.kts)`
Model	fixed lifecycle	task graph
Style	declarative, convention-driven	flexible, scriptable
Speed	steady	incremental builds + build cache, usually faster on big projects
Trade-off	stricter, more uniform	faster, easier to over-customize

Spring BootPage 3

Parent POM, Dependency Management and Starters

1. The parent POM and the BOM

spring-boot-starter-parent as <parent> gives a BOM of tested versions
Also sets plugin config, Java version, UTF-8, resource filtering
Declare managed deps with no <version>
Override: property <spring-data-bom.version> or explicit <version>

xml

<parent>
  <artifactId>spring-boot-starter-parent</artifactId>
</parent>
<dependency>
  <artifactId>spring-boot-starter-web</artifactId>
</dependency>

no version on the dependency

2. No parent allowed? Import the BOM

Company parent POM: import spring-boot-dependencies in <dependencyManagement>
Gradle: the io.spring.dependency-management plugin

xml

<dependencyManagement><dependencies>
  <dependency>
    <artifactId>spring-boot-dependencies</artifactId>
    <type>pom</type>
    <scope>import</scope>
  </dependency>
</dependencies></dependencyManagement>

Spring BootPage 4

Project Layout, Main Class and @SpringBootApplication

1. Standard Layout

Path	Holds
`src/main/java`	application code
`src/main/resources`	`application.properties` or `.yml`, `static/`, `templates/`
`src/test/java`	tests

2. The Main Class

SpringApplication.run creates the ApplicationContext
Then runs auto-configuration
Then starts the embedded server

java

package com.example.demo;
@SpringBootApplication
public class DemoApplication {
  public static void main(String[] args) {
    SpringApplication.run(DemoApplication.class, args);
  }
}

Spring BootPage 5

Running and Packaging the App

1. Run and Build

Dev run: ./mvnw spring-boot:run or ./gradlew bootRun
Or the IDE run button on the main class

Tool	Package command	Output
Maven	`./mvnw clean package`	`target/demo-0.0.1-SNAPSHOT.jar`
Gradle	`./gradlew bootJar`	`build/libs/`

2. Run the Packaged App

Run the jar with java -jar

Spring BootPage 6

Spring Boot Setup Cheat Sheet

1. Bootstrap

Go to start.spring.io, or the IDE wizard
Pick build tool, Boot version, Java version
Packaging jar, then add only the starters you need

2. Commands

Goal	Maven	Gradle
Run in dev	`./mvnw spring-boot:run`	`./gradlew bootRun`
Package	`./mvnw clean package`	`./gradlew bootJar`
Run jar	`java -jar app.jar`

Spring BootPage 7

Check yourself

The main class is in com.example.demo. A @RestController sits in com.example.api. The app starts fine, but its endpoint returns 404. Why?

Component scan covers only the main class's package and its sub-packages
com.example.api is a sibling, so the controller bean is never registered
Fix: move it under com.example.demo, or set scanBasePackages

A pom uses spring-boot-starter-parent but declares spring-boot-starter-web with <version>2.5.0</version>. What is the bug?

The parent's BOM already manages that version, so the pinned one overrides it
It can drift from the other Boot libraries and cause mismatches
Remove the <version> tag

java -jar target/demo.jar fails with no main manifest attribute. What is the likely cause?

Starter	Brings
`-web`	MVC + Tomcat + Jackson
`-data-jpa`	JPA + Hibernate + Spring Data
`-test`	JUnit, Mockito, Spring test
`-security`	Spring Security
`-validation`	Bean Validation
`-actuator`	health and metrics

	Executable fat jar	War
Server	Embedded (Tomcat)	External servlet container
Libs	Nested, via `spring-boot-maven-plugin` / Boot Gradle plugin	Deployed into the container
Extra step	`java -jar` and go	Extend `SpringBootServletInitializer`