jacoco : Cannot exclude classes

Question

I have a maven project and I want to use jacoco for code coverage. Here is the relevant section of my pom

Answer 1

I solved the duplication issue by adding <phase>prepare-package</phase> to the report execution task:

<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.5</version>
  <executions>
    <execution>
      <id>prepare-agent</id>
      <goals>
      <goal>prepare-agent</goal>
      </goals>
    </execution>
    <execution>
      <id>report</id>
      <phase>prepare-package</phase>
      <goals>
      <goal>report</goal>
      </goals>
    </execution>
  </executions>
</plugin>

Answer 2

** is for traversing into underlying directories and different than * which is a character wild card for names. Avoiding ** can result into undesirable effect.

Answer 3

Property excludes of report goal specifies which files should be excluded from analysis during generation of report. In case of /path/tp/my/project/target/classes/META-INF/bundled-dependencies/some-third-party-1-jar-with-dependencies.jar@org/slf4j/event/EventConstants.class file is /path/tp/my/project/target/classes/META-INF/bundled-dependencies/some-third-party-1-jar-with-dependencies.jar , and the rest is about class in JAR file.

Therefore as one of examples of correct configuration:

<configuration>
  <excludes>
    <exclude>META-INF/**</exclude>
  </excludes>
</configuration>

As a proof having pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.example</groupId>
  <artifactId>example</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.jacoco</groupId>
        <artifactId>jacoco-maven-plugin</artifactId>
        <version>0.8.1</version>
      </plugin>
    </plugins>
  </build>

</project>

src/main/java/Example.java

public class Example {
}

and src/test/java/ExampleTest.java

public class ExampleTest {
  @org.junit.Test
  public void test() {
  }
}

Execution of

mvn clean jacoco:prepare-agent package
mkdir target/classes/META-INF/
cp ~/.m2/repository/org/slf4j/slf4j-api/1.4.2/slf4j-api-1.4.2.jar target/classes
cp ~/.m2/repository/org/slf4j/slf4j-api/1.7.7/slf4j-api-1.7.7.jar target/classes/META-INF
mvn jacoco:report

will fail with message

Error while analyzing /private/tmp/j/target/classes/slf4j-api-1.4.2.jar@org/slf4j/helpers/BasicMarker.class. Can't add different class with same name: org/slf4j/helpers/BasicMarker

while same execution with pom.xml containing exclusion of META-INF/**

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">
  <modelVersion>4.0.0</modelVersion>

  <groupId>org.example</groupId>
  <artifactId>example</artifactId>
  <version>1.0-SNAPSHOT</version>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.12</version>
      <scope>test</scope>
    </dependency>
  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.jacoco</groupId>
        <artifactId>jacoco-maven-plugin</artifactId>
        <version>0.8.1</version>
        <configuration>
          <excludes>
            <exclude>META-INF/**</exclude>
          </excludes>
        </configuration>
      </plugin>
    </plugins>
  </build>

</project>

will succeed.

As a side note: semantic of property excludes of prepare-agent goal is different - it specifies class names (regardless of their on-disk location) that should be excluded from instrumentation during execution of tests.