Building an Executable JAR — Spring Technical Interview Questions & Answers

The fat/uber JAR with an embedded server.

Building an Executable JAR

  • Boot builds a fat JAR that contains your code, libraries, and embedded server.
  • One file to run: java -jar app.jar.
  • No need to install Tomcat separately for that style of deploy.
  • Created by the Spring Boot packaging plugin.
  • Confusing a thin library JAR with Boot’s executable uber JAR.
  • Fat JAR = app + deps + embedded server.

Technical Interview Tip: Executable JAR runs with java -jar and embeds the server.

Code Examples for Building an Executable JAR

Building an Executable JAR — working example

// Typical layout after Initializr (Maven):
// src/main/java/.../DemoApplication.java
// src/main/resources/application.properties
// pom.xml → spring-boot-starter-web

import org.springframework.boot.CommandLineRunner;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
class BootHooks {
  @Bean
  CommandLineRunner seed() {
    return args -> System.out.println("app ready: " + String.join(",", args));
  }
}

Building an Executable JAR — create projects via Initializr/STS; run the @SpringBootApplication main class or package an executable jar.

How to Explain Building an Executable JAR to an Interviewer

What is Building an Executable JAR (sb)?

Used for a short Building an Executable JAR sb example a small REST app Not just the heading

Give one small example of Building an Executable JAR (sb).

the smallest Building an Executable JAR sb example you can type The fat/uber JAR with an embedded server

What mistake do beginners make with Building an Executable JAR (sb)?

only saying “Building an Executable JAR sb” with no example Show the fix

Where do you use Building an Executable JAR (sb)?

a small REST app a short Building an Executable JAR sb example