Spring Boot – JaCoCo Integration

JaCoCo (Java Code Coverage) is a popular open-source toolkit for measuring and reporting code coverage in Java projects. When integrated with Spring Boot, it helps ensure your tests are effectively covering your application logic, improving reliability and maintainability.

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What is JaCoCo?

JaCoCo is a free Java code coverage library distributed under the Eclipse Public License. It works with JUnit, TestNG, and other test frameworks, providing:

• Line coverage – How many lines of code were executed.
• Branch coverage – How many decision branches were executed.
• Instruction coverage – Low-level bytecode execution detail.

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Why Use JaCoCo with Spring Boot?

• Measure test effectiveness – Ensure your unit and integration tests are covering critical logic.
• Improve code quality – Detect untested and potentially faulty code.
• CI/CD integration – Fail builds based on coverage thresholds.
• Track regressions – Ensure code coverage doesn’t drop over time.

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Step-by-Step Integration of JaCoCo in Spring Boot

1. Add JaCoCo Plugin to pom.xml (Maven Projects)

<build>
    <plugins>
        <!-- JaCoCo plugin -->
        <plugin>
            <groupId>org.jacoco</groupId>
            <artifactId>jacoco-maven-plugin</artifactId>
            <version>0.8.10</version> <!-- Check for latest version -->
            <executions>
                <execution>
                    <goals>
                        <goal>prepare-agent</goal>
                    </goals>
                </execution>
                <execution>
                    <id>report</id>
                    <phase>prepare-package</phase>
                    <goals>
                        <goal>report</goal>
                    </goals>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

2. Run Tests and Generate Coverage Report

Execute:

mvn clean test

To generate the report:

mvn jacoco:report

3. View the Report

Open the report in your browser:

target/site/jacoco/index.html

You’ll see:

• Coverage by class
• Missed instructions
• Branch and line coverage visualization

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Example Directory Structure

src/
├── main/
│   └── java/
│       └── com.example.demo/
│           └── MyService.java
└── test/
    └── java/
        └── com.example.demo/
            └── MyServiceTest.java

JaCoCo will detect and include all tests from src/test.

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Custom Configuration Options

Set Coverage Thresholds

Fail the build if the coverage is below the set threshold:

<configuration>
    <rules>
        <rule>
            <element>BUNDLE</element>
            <limits>
                <limit>
                    <counter>LINE</counter>
                    <value>COVEREDRATIO</value>
                    <minimum>0.80</minimum>
                </limit>
            </limits>
        </rule>
    </rules>
</configuration>

Exclude Classes from Coverage

To ignore generated or config classes:

<configuration>
    <excludes>
        <exclude>**/config/**</exclude>
        <exclude>**/dto/**</exclude>
    </excludes>
</configuration>

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Integration with CI/CD (GitHub Actions Example)

- name: Run tests and generate JaCoCo report
  run: mvn clean verify

You can use plugins like codecov or coveralls to upload the report:

- name: Upload coverage to Codecov
  uses: codecov/codecov-action@v4
  with:
    files: target/site/jacoco/jacoco.xml

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Integration with SonarQube

To send JaCoCo coverage data to SonarQube:

<properties>
    <sonar.coverage.jacoco.xmlReportPaths>target/site/jacoco/jacoco.xml</sonar.coverage.jacoco.xmlReportPaths>
</properties>

Then run:

mvn clean verify sonar:sonar

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JaCoCo vs Other Tools

Feature	JaCoCo	Cobertura	Clover
Active development	✅ Yes	❌ No	❌ No
Integration with IDEs	✅	✅	✅
CI/CD friendly	✅	⚠️ (limited)	❌
Branch coverage	✅	❌	✅

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Best Practices

• ✅ Aim for meaningful tests, not just high coverage.
• 🧪 Cover edge cases and failure paths.
• 📊 Set and enforce coverage baselines in CI.
• ⚙️ Exclude generated and config classes to avoid skewed reports.

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Conclusion

JaCoCo + Spring Boot is a powerful combo to ensure your code is well-tested, maintainable, and production-ready. It integrates smoothly with Maven, CI/CD tools, and quality dashboards like SonarQube.

By automating test coverage tracking, you reduce bugs and improve code health—essential for modern, agile Java development.

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