How to check code coverage with JaCoCo agent?

Question

I am going to deploy application with JaCoCo agent to production environment to let it work for some time. The result should help me identify the parts of code I can get rid of.

I started some research around the topic and prepared HelloWorld application:

public class HelloWorld {

    public static void main(String[] args) {
        System.out.println("Hello world");
    }
}

Then I compiled the class: "javac HelloWorld.java" and got HelloWorld.class file.

Now I run the app with the following command: "java -javaagent:jacocoagent.jar HelloWorld" the program executes and jacoco binary is generated. The file contains some binary data.

Everything looks fine but the coverage report shows 0% coverage although it should be 100%.

Has anyone faced this issue or correct me what I am doing the bad way?

Do you have any tests? If you don't have any test code coverage will be 0% — cyroxis
– cyroxis, Commented Jun 16, 2015 at 14:15
I don't have any tests, my goal is to identify dead code in legacy project and came up with idea of using JaCoCo. I am executing my app with agent, so class is loaded and method executed, shouldn've it been visible in coverage report? — user3450486
– user3450486, Commented Jun 16, 2015 at 14:32

Blake Yarbrough · Accepted Answer · 2015-06-16 16:04:56Z

2

I generated full report using this steps. Since I use maven for this kind of operations I added maven after your steps. I created HelloWorld.java just copying from your question. Then I follow these steps:

javac HelloWorld.java which outputs HelloWorld.class Then I created jacoco.exec by executing java -javaagent:jacocoagent.jar HelloWorld

Then I created a pom.xml file which contents are like this.

<?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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>pom</packaging>

    <name>test</name>


    <build>
        <plugins>
            <plugin>
                <groupId>org.jacoco</groupId>
                <artifactId>jacoco-maven-plugin</artifactId>
                <version>0.7.5.201505241946</version>
            </plugin>
        </plugins>
    </build>

After that I created a target/classes directory. I copied jacoco.exec to target/ and HelloWorld.class to target/classes.

Then I executed mvn jacoco:report which generates a report to target/site/jacoco. Which contains correct coverage information.

I know using maven may not sound good for a simple application. But I don't know any other way to generate reports from jacoco.exec. By the way your maven plugin version and jacocoagent version must match.

And here the result I get. result

edited Jun 16, 2015 at 16:04

Blake Yarbrough

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answered Jun 16, 2015 at 14:47

bhdrkn

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2 Comments

user3450486 Over a year ago

Thanks for your solution. As far as I understand you used maven together with jacoco plugin just to interpret binary file jacoco.exec and see html report. I did the same with IntelliJ and Jenkins plugins (no mvn) and have 0% report.

user3450486 Over a year ago

Did the same as you and it works. So it looks like IntelliJ IDEA JaCoCo plugin as well as Jenkins plugin can't generate correct reports in this case because they generate reports with 0% coverage.

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