Knowledge Base > Cover CLI > Measuring the coverage of a main method

Measuring the coverage of a main method

This article provides guidance how to measure and visualize the coverage associated to executing a Java main class.

• Using Intellij IDEA
• Maven projects
• Gradle projects

Using Intellij IDEA

1. Load the project in Intellij IDEA.
2. Right-click on the small green ‘play’ button next to the method and then ‘Run <main method> with Coverage’:

Maven projects

1. Compile the project:

   mvn compile
   

2. Copy the project dependencies using the Maven goal dependency:copy-dependencies:

   mvn dependency:copy-dependencies
   

3. Get the JaCoCo agent:

   mvn dependency:copy -Dartifact=org.jacoco:org.jacoco.agent:0.8.8:jar:runtime
   

4. Run the main method with the JaCoCo agent:

   java -javaagent:target/dependency/org.jacoco.agent-0.8.8-runtime.jar \
      -cp 'target/classes/:target/dependency/*' \
      com.example.YourMainClass
   

5. The coverage report is at ./jacoco.exec, you can now visualize it in Intellij.

Complete example on Spring Pet Clinic:

git clone https://github.com/spring-projects/spring-petclinic
cd spring-petclinic

mvn compile
mvn dependency:copy-dependencies
mvn dependency:copy -Dartifact=org.jacoco:org.jacoco.agent:0.8.8:jar:runtime

java -javaagent:target/dependency/org.jacoco.agent-0.8.8-runtime.jar \
   -cp 'target/classes/:target/dependency/*' \
   org.springframework.samples.petclinic.PetClinicApplication

Gradle projects

1. Modify the build.gradle file to configure the application and jacoco plugins this way:

   plugins {
     id 'application'
     id 'jacoco'
   }
   
   application {
     mainClass = 'com.example.YourMainClass'
   }
   
   jacoco {
     applyTo run
   }
   

2. Run the application

   ./gradlew run
   

3. The coverage report is at ./build/jacoco/run.exec, you can now visualize it in Intellij.

Complete example on Spring Pet Clinic:

git clone https://github.com/spring-projects/spring-petclinic
cd spring-petclinic

# modify the build.gradle file, to introduce the following changes:
git diff build.gradle
 --- a/build.gradle
 +++ b/build.gradle
 @@ -2,6 +2,8 @@ plugins {
    id 'org.springframework.boot' version '2.6.6'
    id 'io.spring.dependency-management' version '1.0.11.RELEASE'
    id 'java'
 +  id 'application'
 +  id 'jacoco'
  }

  apply plugin: 'java'
 @@ -39,3 +41,11 @@ dependencies {
  test {
    useJUnitPlatform()
  }
 +
 +application {
 +  mainClass = 'org.springframework.samples.petclinic.PetClinicApplication'
 +}
 +
 +jacoco {
 +  applyTo run
 +}

# run the application
./gradlew run