Maven compilation error: package does not exist

When building a multi-module Maven project, everything works fine for the first two modules, but compilation fails for module 3 with errors like:

[ERROR] COMPILATION ERROR :
[INFO] -------------------------------------------------------------
[ERROR] \Module3\src\com\company\sharedartifact\package\SomeClass.java:[8,55] package com.company.sharedartifact.package does not exist
[ERROR] \Module3\src\com\company\sharedartifact\package\SomeClass.java:[9,55] package com.company.sharedartifact.package does not exist
[ERROR] \Module3\src\com\company\sharedartifact\package\SomeClass.java:[17,85] cannot find symbol
symbol  : class SomeOtherClass

This issue arises despite the required JAR being listed as a dependency in both module 2 and module 3. Attempts to fix it by:

Adding the dependency explicitly in module 3
Relying on transitive dependencies
Refreshing and re-downloading dependencies
…have not resolved the issue.

Why This Happens

This type of error often stems from:

Incorrect Transitive Dependency Resolution: Maven does not always correctly propagate dependencies between modules.
Classpath Issues in IDEs: Tools like Eclipse can sometimes misconfigure the build classpath for multi-module projects.
Build Order Problems: Modules may not compile in the correct order, leading to missing artifacts during the build process.

Solution

Here’s a step-by-step approach to fix the issue:

1. Verify Dependency Declaration

Ensure the dependencies are correctly defined in the POM files. For module 3, explicitly declare the required dependencies:

Module 3 POM:

<dependency>
    <groupId>com.company</groupId>
    <artifactId>Module2</artifactId>
    <version>0.0.1-SNAPSHOT</version>
</dependency>

<dependency>
    <groupId>com.company</groupId>
    <artifactId>SharedArtifact</artifactId>
    <version>1.1</version>
</dependency>

2. Check the Parent POM

Ensure the parent POM defines all modules and dependencies properly:

<modules>
    <module>module-1</module>
    <module>module-2</module>
    <module>module-3</module>
</modules>

3. Build Modules in the Correct Order

Run the following command to build the modules step-by-step:

mvn clean install -pl module-1,module-2,module-3

This ensures each module is compiled and installed sequentially.

4. Use Dependency Plugin to Analyze Issues

Run the Maven Dependency plugin to inspect your dependency tree:

mvn dependency:tree

This helps identify conflicting or missing dependencies.

5. Configure Eclipse Properly

If you’re using Eclipse, perform these steps:

Right-click the project > Maven > Update Project.
Check “Force Update of Snapshots/Releases.”
Ensure M2_REPO is set up correctly in your Eclipse classpath.

6. Clean and Rebuild

Sometimes, stale artifacts can cause issues. Try the following:

mvn clean install -U

The -U flag forces Maven to update snapshots and releases.

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