13. Structuring your code

Spring Boot does not require any specific code layout to work, however, there are some best practices that help.

13.1 Using the “default” package

When a class doesn’t include a package declaration it is considered to be in the “default package”. The use of the “default package” is generally discouraged, and should be avoided. It can cause particular problems for Spring Boot applications that use @ComponentScan or @EntityScan annotations, since every class from every jar, will be read.


We recommend that you follow Java’s recommended package naming conventions and use a reversed domain name (for example, com.example.project).

13.2 Locating the main application class

We generally recommend that you locate your main application class in a root package above other classes. The @EnableAutoConfiguration annotation is often placed on your main class, and it implicitly defines a base “search package” for certain items. For example, if you are writing a JPA application, the package of the @EnableAutoConfiguration annotated class will be used to search for @Entity items.

Using a root package also allows the @ComponentScan annotation to be used without needing to specify a basePackage attribute.

Here is a typical layout:

 +- example
     +- myproject
         +- Application.java
         +- domain
         |   +- Customer.java
         |   +- CustomerRepository.java
         +- service
         |   +- CustomerService.java
         +- web
             +- CustomerController.java

The Application.java file would declare the main method, along with the basic @Configuration.

package com.example.myproject;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;

public class Application {

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