Multi-module project structure in Spring Boot - Step-by-Step Execution

Concept Flow - Multi-module project structure

Parent Project (pom.xml)

↓

Build Parent -> Build Modules

↓

Modules share dependencies & build

↓

Run individual modules or combined app

The parent project manages common settings and dependencies. Each module has its own code and can be built separately or together.

Execution Sample

Spring Boot

<modules>
  <module>module-a</module>
  <module>module-b</module>
</modules>

This snippet shows the parent pom.xml listing two modules, telling Maven to build them together.

Execution Table

Step	Action	File/Module	Result
1	Read parent pom.xml	parent-pom.xml	Identify modules: module-a, module-b
2	Build module-a	module-a/pom.xml	Compile module-a code, resolve dependencies
3	Build module-b	module-b/pom.xml	Compile module-b code, resolve dependencies
4	Link modules	parent-pom.xml	Modules share common dependencies and build settings
5	Run module-a	module-a	Start module-a application or tests
6	Run module-b	module-b	Start module-b application or tests
7	Build parent	parent-pom.xml	Build all modules together
8	Exit	-	Build and run complete

💡 All modules built and linked successfully, ready to run individually or combined

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
modules	empty	[module-a, module-b]	[module-a, module-b]	[module-a, module-b]	[module-a, module-b]
module-a build status	not built	not built	built	built	built
module-b build status	not built	not built	not built	built	built
parent build status	not built	not built	not built	not built	built

Key Moments - 3 Insights

Why do we need a parent pom.xml in a multi-module project?

The parent pom.xml centralizes common dependencies and build settings so modules don't repeat them. See Step 1 and Step 4 in the execution_table.

Can modules be built and run independently?

Yes, each module has its own pom.xml and can be built or run separately, as shown in Steps 2, 3, 5, and 6.

How does building the parent project affect modules?

Building the parent triggers building all modules together, ensuring consistent versions and dependencies, as in Step 7.

Visual Quiz - 3 Questions

Look at the execution table, what modules does the parent pom.xml list?

A module-a and module-b

B Only module-a

C Only module-b

D No modules listed

💡 Hint

Check Step 1 in the execution_table where parent pom.xml identifies modules

At which step is module-b built?

A Step 2

B Step 3

C Step 5

D Step 7

💡 Hint

Look at the Action and File/Module columns in the execution_table

If the parent pom.xml did not list module-b, what would change in the execution table?

A Step 7 would build only module-b

B Step 2 would be missing

C Step 3 would be missing

D No change

💡 Hint

Modules are identified in Step 1 and built in Steps 2 and 3

Concept Snapshot

Multi-module project uses a parent pom.xml to manage common settings.
Modules have their own pom.xml files and code.
Parent pom lists modules to build together.
Modules can be built/run independently or combined.
This structure keeps code organized and dependencies consistent.

Full Transcript

A multi-module project in Spring Boot uses a parent pom.xml file that lists all modules. Each module has its own pom.xml and code. When building, Maven reads the parent pom.xml to find modules, then builds each module in order. Modules share dependencies and build settings from the parent. You can run modules separately or build the whole project together. This helps keep code organized and avoids repeating dependency info.

Practice

1. What is the main purpose of a multi-module project in Spring Boot?

easy

A. To create multiple databases for one application

B. To run multiple Spring Boot applications simultaneously

C. To split a large project into smaller, manageable parts

D. To avoid using pom.xml files

Solution

1. Step 1: Understand project organization

   Multi-module projects break a big codebase into smaller modules for easier management.

2. Step 2: Identify the main goal

   This splitting helps teams work on parts independently and share code efficiently.

3. Final Answer:

   To split a large project into smaller, manageable parts -> Option C

4. Quick Check:

   Multi-module = smaller parts [OK]

Hint: Think of dividing work into smaller folders [OK]

Common Mistakes:

• Confusing multi-module with running multiple apps
• Thinking it removes the need for pom.xml
• Assuming it creates multiple databases

2. Which file typically manages all modules in a Spring Boot multi-module project?

easy

A. application.properties

B. module-specific application.yml

C. settings.gradle

D. parent pom.xml

Solution

1. Step 1: Identify the build management file

   In Maven-based Spring Boot projects, the parent pom.xml controls all modules.

2. Step 2: Understand file roles

   Other files like application.properties configure app settings, not modules.

3. Final Answer:

   parent pom.xml -> Option D

4. Quick Check:

   Parent pom manages modules [OK]

Hint: Parent pom.xml controls modules [OK]

Common Mistakes:

• Confusing application.properties with module management
• Thinking settings.gradle is used in Maven projects
• Assuming module-specific files manage all modules

3. Given a multi-module project with modules core and web, where web depends on core, what happens if core is not built before web?

medium

A. The web module build will fail due to missing dependencies

B. The web module will build successfully without core

C. Both modules will build independently without errors

D. The core module will build automatically after web

Solution

1. Step 1: Understand module dependencies

   If web depends on core, it needs core built first to access its code.

2. Step 2: Consequence of build order

   Building web without core causes missing dependency errors and build failure.

3. Final Answer:

   The web module build will fail due to missing dependencies -> Option A

4. Quick Check:

   Dependent module needs dependency built first [OK]

Hint: Build dependencies before dependents [OK]

Common Mistakes:

• Assuming modules build independently
• Thinking build order does not matter
• Believing dependent modules build automatically

4. You have a multi-module Spring Boot project but the web module cannot find classes from the core module. What is the most likely cause?

medium

A. The core module is not listed as a dependency in web's pom.xml

B. The web module has no application.properties

C. The parent pom.xml is missing the modules section

D. The core module is using a different Java version

Solution

1. Step 1: Check module dependencies

   If web cannot find core classes, it likely lacks a dependency declaration on core.

2. Step 2: Verify dependency declaration

   Adding core as a dependency in web's pom.xml fixes class visibility.

3. Final Answer:

   The core module is not listed as a dependency in web's pom.xml -> Option A

4. Quick Check:

   Missing dependency causes class not found [OK]

Hint: Always declare module dependencies in pom.xml [OK]

Common Mistakes:

• Ignoring dependency declarations
• Thinking application.properties affects class visibility
• Assuming Java version mismatch causes missing classes

5. In a multi-module Spring Boot project, you want to share common utility classes across modules without duplicating code. Which approach is best?

hard

A. Copy utility classes into each module's source folder

B. Create a separate common module and add it as a dependency to other modules

C. Put all utility classes in the parent pom.xml

D. Use application.properties to share utility classes

Solution

1. Step 1: Identify code sharing strategy

   To avoid duplication, create a dedicated common module for shared utilities.

2. Step 2: Use module dependencies

   Other modules add common as a dependency to access shared code cleanly.

3. Final Answer:

   Create a separate common module and add it as a dependency to other modules -> Option B

4. Quick Check:

   Shared code in common module [OK]

Hint: Use a common module for shared code [OK]

Common Mistakes:

• Copying code causes duplication and maintenance issues
• Trying to put code in pom.xml (not for code)
• Using properties files to share classes