Deep Dive into the Clean Lifecycle in Maven

The Clean Lifecycle in Maven is responsible for removing old build artifacts and ensuring that the workspace is clean before a new build starts. This prevents outdated or conflicting files from interfering with a fresh build.

1️⃣ Clean Lifecycle Overview

The Clean Lifecycle consists of three phases:

1. pre-clean → Runs any custom tasks before cleaning.
2. clean → Deletes all previously compiled and packaged artifacts.
3. post-clean → Runs any custom tasks after cleaning.

Each phase can have goals (specific tasks assigned to it), which execute underlying tasks (actions performed inside each goal).

2️⃣ Clean Lifecycle Structure

Lifecycle: Clean │ ├── Phase: pre-clean │ ├── (Custom goals can be added) │ ├── Phase: clean │ ├── Goal: maven-clean-plugin:clean │ │ ├── Task: Locate the `target/` directory │ │ ├── Task: Delete all files and subdirectories inside `target/` │ │ ├── Task: Remove additional directories (if configured) │ │ ├── Task: Log cleanup results │ └── Phase: post-clean ├── (Custom goals can be added) 

The main goal used in the clean phase is:

• maven-clean-plugin:clean → Deletes old build artifacts.

3️⃣ Clean Lifecycle Phases, Goals, and Tasks

🔹 Phase 1: pre-clean

📌 Purpose:

• Runs before cleaning starts.
• No default goals are assigned, but developers can add custom goals.

📌 Possible Custom Goals:

• Backing up important files before cleaning.
• Logging information before cleanup.

📌 Example Custom Plugin

<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-antrun-plugin</artifactId> <version>1.8</version> <executions> <execution> <phase>pre-clean</phase> <goals> <goal>run</goal> </goals> <configuration> <tasks> <echo>Backup completed before cleaning</echo> </tasks> </configuration> </execution> </executions> </plugin> 

👉 This adds a custom goal that logs a message before cleaning.

🔹 Phase 2: clean

📌 Purpose:

• Deletes old build artifacts.
• Ensures a clean workspace for a fresh build.

📌 Default Goal:

• maven-clean-plugin:clean

📌 Tasks Inside This Goal:

1. Locate the target/ directory (default build output location).
2. Delete everything inside target/ (compiled .class files, packaged .jar files, logs, and reports).
3. Remove additional directories (if configured in pom.xml).
4. Log cleanup status (successful or failed deletions).

📌 How to Execute:

mvn clean 

🚀 This will trigger:

• The clean phase, which calls the maven-clean-plugin:clean goal.
• This goal will delete the target/ directory.

📌 Example Plugin Configuration in pom.xml:

<build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-clean-plugin</artifactId> <version>3.2.0</version> <configuration> <filesets> <fileset> <directory>logs</directory> </fileset> <fileset> <directory>temp</directory> </fileset> </filesets> </configuration> </plugin> </plugins> </build> 

👉 This configuration tells Maven to delete logs/ and temp/ directories in addition to target/ when mvn clean is executed.

📌 Before Running mvn clean:

my-project/ ├── src/ ├── pom.xml ├── target/ │ ├── my-project-1.0.jar │ ├── compiled-classes/ │ ├── test-reports/ └── logs/ ├── error.log 

📌 After Running mvn clean:

my-project/ ├── src/ ├── pom.xml 

🚀 Result:

• The target/ and logs/ directories are deleted.
• The workspace is clean.

🔹 Phase 3: post-clean

📌 Purpose:

• Runs after cleaning is completed.
• No default goals, but can be customized.

📌 Possible Custom Goals:

• Logging success/failure of the clean operation.
• Running additional cleanup scripts.

📌 Example: Logging Cleanup Completion

<plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-antrun-plugin</artifactId> <version>1.8</version> <executions> <execution> <phase>post-clean</phase> <goals> <goal>run</goal> </goals> <configuration> <tasks> <echo>Cleaning completed successfully.</echo> </tasks> </configuration> </execution> </executions> </plugin> 

👉 This logs "Cleaning completed successfully." after mvn clean runs.

4️⃣ Clean Lifecycle Summary Table

5️⃣ Key Takeaways

✅ Maven Clean Lifecycle ensures a fresh build environment by removing old artifacts.

✅ It has three phases (pre-clean, clean, post-clean).

✅ The main goal is maven-clean-plugin:clean, which deletes the target/ directory.

✅ Custom goals can be added to pre-clean and post-clean for extra functionality.

✅ Running mvn clean executes only the clean lifecycle (does not trigger compilation or testing).

6️⃣ FAQ

❓ Q: Does mvn clean also compile my project?

No! mvn clean only deletes files. It does not compile anything.

❓ Q: Can I delete additional folders like logs/?

Yes! Add them in pom.xml using the maven-clean-plugin configuration.

❓ Q: What happens if target/ doesn't exist?

Nothing bad—it simply skips the deletion step.

❓ Q: Can I run mvn clean package together?

Yes! It will first clean, then compile, test, and package:

mvn clean package 

👉 This deletes old files first, then builds a fresh JAR/WAR.

7️⃣ Final Thoughts

The Clean Lifecycle is simple but essential for avoiding old, stale files in your project. It ensures that each build starts with a fresh environment, reducing the risk of conflicts.