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Maven

plugin dependency config jar scope...

<pluginManagement> in parent, it declares plugin versions and config, but does not run the plugin in any module until it's declared in of that module

Build

In Maven, the <build> tag is used in the pom.xml to configure how the project is built, including:

  • Output directories
  • Final artifact name
  • Plugins to use (and their configuration)
  • Resources to include

<plugins> in parent

  • Runs only for the parent module itself
  • Child modules do not inherit these plugins or run them unless they declare their own block

jacoco-maven-plugin

Goal Description
Measure code coverage Tracks how much of your Java code is executed during test runs
Generate coverage reports Produces HTML, XML, and CSV reports for analysis
Enforce coverage rules Can fail the build if line or branch coverage is below threshold
Supports unit and integration tests Works with Surefire (unit tests) and Failsafe (integration tests) 
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<build>
<plugins>
    <plugin>
    <groupId>org.jacoco</groupId>
    <artifactId>jacoco-maven-plugin</artifactId>
    <version>0.8.11</version>
    <executions>
        <!-- Prepares coverage instrumentation -->
        <execution>
        <id>prepare-agent</id>
        <goals>
            <goal>prepare-agent</goal>
        </goals>
        </execution>

        <!-- Generates report after tests -->
        <execution>
        <id>report</id>
        <phase>prepare-package</phase>
        <goals>
            <goal>report</goal>
        </goals>
        </execution>

        <!-- Fail build if coverage is too low -->
        <execution>
        <id>check</id>
        <goals>
            <goal>check</goal>
        </goals>
        <configuration>
            <rules>
            <rule>
                <element>BUNDLE</element>
                <limits>
                <limit>
                    <counter>LINE</counter>
                    <value>COVEREDRATIO</value>
                    <minimum>0.80</minimum>
                </limit>
                <limit>
                    <counter>BRANCH</counter>
                    <value>COVEREDRATIO</value>
                    <minimum>0.70</minimum>
                </limit>
                </limits>
            </rule>
            </rules>
        </configuration>
        </execution>
    </executions>
    </plugin>
</plugins>
</build>

After running mvn test or mvn verify, reports are generated in:

  • target/site/jacoco/index.html (HTML report)
  • target/site/jacoco/jacoco.xml (XML for CI tools like SonarQube)

Coverage Types

Metric Description
Line % of lines executed
Branch % of control structures covered
Method % of methods tested
Class % of classes touched

maven-checkstyle-plugin

Goal Description
Enforce coding standards Validates Java code against a defined style guide (e.g., Google, Sun, custom)
Ensure code consistency Helps teams maintain uniform formatting and structure
Catch style violations early Detects spacing, naming, import order, and other formatting issues
Generate style violation reports Produces HTML and XML reports for visual inspection or CI pipelines
Fail builds on violations Prevents code with style issues from passing CI/CD or being merged

The maven-checkstyle-plugin integrates Checkstyle into your Maven build to enforce Java coding standards and styles across your project.

It helps catch:

  • Improper naming conventions
  • Braces, spacing, line length issues
  • Unused imports or fields
  • Code style violations based on rules
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<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-checkstyle-plugin</artifactId>
  <version>3.3.0</version>
  <executions>
    <execution>
      <id>validate</id>
      <phase>validate</phase>
      <goals>
        <goal>check</goal>
      </goals>
    </execution>
  </executions>
  <configuration>
    <configLocation>checkstyle.xml</configLocation>
    <suppressionsLocation>checkstyle-suppressions.xml</suppressionsLocation>
    <maxAllowedViolations>0</maxAllowedViolations>
    <propertyExpansion>
      <subpackage>com.example.project</subpackage>
      <checkstyle.cache.file>${project.build.directory}/checkstyle-cachefile</checkstyle.cache.file>
    </propertyExpansion>
    <encoding>UTF-8</encoding>
    <consoleOutput>true</consoleOutput>
    <failsOnError>true</failsOnError>
  </configuration>
</plugin>
Tag Purpose
configLocation The Checkstyle ruleset XML. Use built-in like google_checks.xml, or define your own.
suppressionsLocation XML file listing rules/files to ignore. Useful for legacy files or generated code.
maxAllowedViolations Maximum allowed rule violations before build fails (usually 0 for strict mode).
propertyExpansion Allows defining variables (like subpackage) for dynamic usage inside the Checkstyle config.
encoding Ensures source is read correctly (typically UTF-8).
consoleOutput Print violations to the console output for easy debugging.
failsOnError Set true to fail build if violations are found.

propertyExpansion Use Case: subpackage

This is useful for rules that match or enforce package structure.

In POM: 

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<propertyExpansion>
  <subpackage>com.mycompany.core</subpackage>
</propertyExpansion>

In checkstyle.xml: 

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<module name="RegexpPackage">
  <property name="format" value="^${subpackage}(\..+)*$"/>
</module>

This enforces that all classes belong to com.mycompany.core or subpackages.

Output Reports

When you run:

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mvn checkstyle:checkstyle

You’ll get reports in:

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target/site/checkstyle.html
target/site/checkstyle-result.xml
Feature Description
Code Style Enforcement Enforces consistent formatting and structure
Report Generation Outputs HTML and XML reports
Fail-on-Violation Ensures CI builds fail when code violates style
Configurable Rules Use custom or built-in rules
Suppression Support Ignore violations for specific classes/files
Property Expansion Inject variables (like subpackage)

aven-surefire-plugin

Goal Description
Run unit tests Executes tests written with JUnit, TestNG, or other supported frameworks
Integrate with Maven lifecycle Automatically runs tests during the test phase
Generate test reports Produces text and XML reports under target/surefire-reports/
Detect test failures Fails the build if any unit test fails (configurable)
Support test customization Allows inclusion/exclusion patterns, parallel test execution, and filtering 
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<plugin>
  <groupId>org.apache.maven.plugins</groupId>
  <artifactId>maven-surefire-plugin</artifactId>
  <version>3.0.0-M9</version>
  <configuration>
    <includes>
      <include>**/*Tests.java</include>
      <include>**/*Tests.json</include>
    </includes>
    <runOrder>alphabetical</runOrder>
    <reportsDirectory>${project.basedir}/target/surefire-reports</reportsDirectory>
    <testFailureIgnore>false</testFailureIgnore>
  </configuration>
</plugin>

cheatsheet

  1. delete a specific dependency from your local Maven cache (~/.m2/repository) and force Maven to re-download it cleanly from the remote repository 
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    mvn dependency:purge-local-repository -DmanualInclude="org.bouncycastle:bcprov-jdk15on"