Spring Boot Cheatsheet

Setup

Use this Spring Boot reference while you build software engineering projects, review code for technical interview prep, or polish examples for a software engineer resume.

Project Generation

Use this Spring Boot programming cheatsheet as a backend developer reference while you build Java REST APIs. For full-stack work, keep the React cheatsheet, SQL cheatsheet, Git cheatsheet, and Python cheatsheet nearby for UI, data, version control, and automation syntax.

Use Spring Initializr or the CLI to scaffold a project.

# Spring CLI (install via SDKMAN or brew)
spring init --dependencies=web,data-jpa,postgresql,validation,security \
  --build=maven --java-version=21 my-app

Initializr settings: - Project: Maven or Gradle (Kotlin DSL) - Language: Java 21+ (LTS) - Spring Boot: 3.x (latest stable) - Packaging: Jar (default); War only for servlet containers

Maven `pom.xml` Essentials

<parent>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter-parent</artifactId>
  <version>3.3.2</version>
</parent>

<dependencies>
  <!-- Web / REST -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>

  <!-- JPA + Hibernate -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-jpa</artifactId>
  </dependency>

  <!-- Validation (Jakarta Bean Validation) -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-validation</artifactId>
  </dependency>

  <!-- Security -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-security</artifactId>
  </dependency>

  <!-- PostgreSQL driver -->
  <dependency>
    <groupId>org.postgresql</groupId>
    <artifactId>postgresql</artifactId>
    <scope>runtime</scope>
  </dependency>

  <!-- Dev Tools (hot reload, disable caching in dev) -->
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-devtools</artifactId>
    <scope>runtime</scope>
    <optional>true</optional>
  </dependency>

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

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

Gradle (`build.gradle.kts`) Essentials

plugins {
    java
    id("org.springframework.boot") version "3.3.2"
    id("io.spring.dependency-management") version "1.1.5"
}

dependencies {
    implementation("org.springframework.boot:spring-boot-starter-web")
    implementation("org.springframework.boot:spring-boot-starter-data-jpa")
    implementation("org.springframework.boot:spring-boot-starter-validation")
    implementation("org.springframework.boot:spring-boot-starter-security")
    runtimeOnly("org.postgresql:postgresql")
    developmentOnly("org.springframework.boot:spring-boot-devtools")
    testImplementation("org.springframework.boot:spring-boot-starter-test")
}

Main Application Class

package com.example.myapp;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication   // = @Configuration + @EnableAutoConfiguration + @ComponentScan
public class MyAppApplication {
    public static void main(String[] args) {
        SpringApplication.run(MyAppApplication.class, args);
    }
}

@SpringBootApplication scans the package it lives in and all sub-packages. Put it at the root package.

Common Starters Reference

Starter	Brings In
`spring-boot-starter-web`	Spring MVC, Tomcat, Jackson
`spring-boot-starter-webflux`	Project Reactor, Netty (reactive)
`spring-boot-starter-data-jpa`	Hibernate, Spring Data
`spring-boot-starter-data-mongodb`	MongoDB driver, Spring Data Mongo
`spring-boot-starter-data-redis`	Lettuce, Spring Data Redis
`spring-boot-starter-security`	Spring Security filter chain
`spring-boot-starter-oauth2-resource-server`	JWT / opaque-token validation
`spring-boot-starter-validation`	Hibernate Validator (Jakarta EE)
`spring-boot-starter-actuator`	Health, metrics, info endpoints
`spring-boot-starter-mail`	JavaMailSender
`spring-boot-starter-cache`	Spring Cache abstraction
`spring-boot-starter-aop`	AspectJ / Spring AOP
`spring-boot-starter-test`	JUnit 5, Mockito, AssertJ, MockMvc

Running the Application

# Maven
./mvnw spring-boot:run

# Gradle
./gradlew bootRun

# Fat JAR
./mvnw package
java -jar target/my-app-0.0.1-SNAPSHOT.jar

# Override properties at runtime
java -jar my-app.jar --server.port=9090 --spring.profiles.active=prod

Project Structure Convention

src/
  main/
    java/com/example/myapp/
      MyAppApplication.java     ← root (place @SpringBootApplication here)
      controller/               ← @RestController classes
      service/                  ← @Service classes
      repository/               ← @Repository / JPA interfaces
      model/                    ← @Entity + DTO classes
      config/                   ← @Configuration classes
      exception/                ← custom exceptions + @ControllerAdvice
    resources/
      application.properties    ← (or application.yml)
      application-dev.properties
      application-prod.properties
      static/                   ← served at "/"
      templates/                ← Thymeleaf / Mustache
  test/
    java/com/example/myapp/     ← mirrors main structure

Auto-configuration Gotchas

Auto-config fires only when a class/bean is not already defined — define your own bean to override.
Check what was configured: --debug flag prints a conditions report.
Exclude specific auto-config: @SpringBootApplication(exclude = DataSourceAutoConfiguration.class).
spring-boot-devtools is not included in the fat JAR by default (optional=true).