Sonar and Gradle Multi-Module Projects

I love Sonar. It is a wonderful way to collect some metrics for your Java projects - hassle-free and wrapped in a sweet-looking UI.  For Maven-based projects Sonar literally works out of the box. Just start up your Sonar instance (assuming you are using the default settings running on localhost) and then you simply fire it off using:

$ mvn sonar:sonar 

A few moments later you should have the metrics available at:

http://localhost:9000/

Well, the past few days I was setting up a multi-module Gradle project for Sonar. Let me start by stating that Gradle is awesome. Having the ability to declare dependencies as one-liners and also being able to customize your scripts easily, yet having sensible defaults, is very nice. Kind of the best of both worlds.

Setting up Sonar for a multi module project, though, is unfortunately a bit more complicated, compared to what I am used to in the Maven world. It is not awfully complicated, but it took me a while to collect all the pieces of information.

Getting your Sonar plugin to just doing something is fairly simple. Just follow the basic steps outlined in the plugin documentation at:

• http://gradle.org/docs/current/userguide/sonar_plugin.html

One differentiator between the Sonar Plugin for Gradle and Maven is, that the Gradle version does not automatically run code coverage analysis. This needs to be manually setup. This is where the official doc just vaguely refers to Cobertura.

First, I tried using Cobertura for code coverage, but I seemed to run into difficulties for my multi-module projects. The Cobertura Plugin is here:

• https://github.com/valkolovos/gradle_cobertura/wiki

By chance I realized that the Sonar guys have a GitHub repository with samples on how to setup sonars for various build systems, including Gradle:

• https://github.com/SonarSource/sonar-examples/

In their examples, they are using JaCoCo, which is not mentioned in the original Gradle docs and maybe I could have continued with Cobertura but it seemed that Sonar was preferring JaCoCo and thus I continued with that.

Some Gradle Sonar Plugin Limitations

The Gradle Sonar Plugin has an annoying limitation, where I can run it for the ROOT project OR for the sub-projects individually. See the following Gradle Jira ticket for details:

• http://issues.gradle.org/browse/GRADLE-1813

Furthermore, I hit the minor issue that I cannot set the links in the Sonar dashboard. This seems to be related to the following Sonar Jira issue:

• https://jira.codehaus.org/browse/SONAR-2749

The JaCoCo code coverage plugin is "slightly less" supported by the Gradle Sonar Plugin, e.g. the  Gradle Plugin does not have an explicit setter for the JacocoReportPath and it assumes the "target" folder as the build directory by default. Therefore you must set explicitly:

props["sonar.jacoco.reportPath"]  = "${buildDirName}/jacoco.exec"

Lastly, I deviated a bit from the SonarSource Gradle example, and instead of System properties, I wanted to use Gradle properties to allow for users to provide non-default Sonar configuration settings (databasem url, jdbc parameters etc.). Well, while setting that up I ran into yet another Gradle Jira issue:

• http://issues.gradle.org/browse/GRADLE-1826

But at the the end, I am happily able to run a multi-module Gradle project with Sonar and collecting Code Coverage statistics.  Here is the relavant code from my build.gradle file:

apply plugin: 'sonar'

sonar {

    if (rootProject.hasProperty('sonarHostUrl')) {
        server.url = rootProject.sonarHostUrl
    }

    database {
        if (rootProject.hasProperty('sonarJdbcUrl')) {
            url = rootProject.sonarJdbcUrl
        }
        if (rootProject.hasProperty('sonarJdbcDriver')) {
            driverClassName = rootProject.sonarJdbcDriver
        }
        if (rootProject.hasProperty('sonarJdbcUsername')) {
            username = rootProject.sonarJdbcUsername
        }
        if (rootProject.hasProperty('sonarJdbcPassword')) {
            password = rootProject.sonarJdbcPassword
        }
    }

    project {
        dynamicAnalysis  = "reuseReports"
        withProjectProperties { props ->
            props["sonar.core.codeCoveragePlugin"] = "jacoco"
            props["sonar.jacoco.reportPath"]       = "${buildDirName}/jacoco.exec"
        }
    }

    println("Sonar parameters used: server.url='${server.url}'; database.url='${database.url}'; database.driverClassName='${database.driverClassName}'; database.username='${database.username}'")

}

subprojects { subproject ->

    ...

    // See http://www.gradle.org/docs/current/userguide/dependency_management.html#sub:configurations
    // and http://www.gradle.org/docs/current/dsl/org.gradle.api.artifacts.ConfigurationContainer.html
    configurations {
        jacoco //Configuration Group used by Sonar to provide Code Coverage using JaCoCo
    }

    // dependencies that are common across all java projects
    dependencies {
        ...
        jacoco group: "org.jacoco", name: "org.jacoco.agent", version: "0.5.3.201107060350", classifier: "runtime"
        ...
    }

    test {
        jvmArgs "-javaagent:${configurations.jacoco.asPath}=destfile=${buildDir}/jacoco.exec,includes=org.your.project.*"
    }
    ...
}

I hope this is useful information for all Gradle users out there.