maven-003: deep-dive-into-clean-lifecycle

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 This prevents outdated or conflicting files from interfering with a fresh build.

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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).

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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.

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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.

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🔹 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.

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🔹 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.

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4️⃣ Clean Lifecycle Summary Table

Phase	Goal	Task Performed
pre-clean	(None by default, custom only)	Runs pre-cleanup actions (e.g., backups, logging).
clean	maven-clean-plugin:clean	Deletes target/ and configured directories.
post-clean	(None by default, custom only)	Runs post-cleanup actions (e.g., logging success).

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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).

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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.

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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.