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Using JUnit 5 In Pre-Java 8 Projects

This post demonstrates how JUnit 5 can be used in pre-Java 8 projects and explains why it could be a good idea.

JUnit 5 requires at least Java 8 as runtime environment, so you want to update your whole project to Java 8. But sometimes there exists reason why you can’t immediately update your project to Java 8. For example, the version of your application server in production only supports Java 7. But an update isn’t be taken quickly because of some issues in your production code.

Now, the question is how can you use JUnit 5 without update your production code to Java 8?

You can set up the Java version separately for production code and for test code .

<!-- in Maven -->
// in Gradle
sourceCompatibility = '7'
targetCompatibility = '7'

compileTestJava {
sourceCompatibility ='8'
targetCompatibility = '8'

Precondition is that you use a Java 8 JDK for your build.

If you try to use Java 8 feature in your Java 7 production code, Maven and Gradle will fail the build.

// Maven
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-compiler-plugin:3.8.0:compile (default-compile) on project junit5-in-pre-java8-projects: Compilation failure
[ERROR] /home/sparsick/dev/workspace/junit5-example/junit5-in-pre-java8-projects/src/main/java/[8,58] lambda expressions are not supported in -source 7
[ERROR]   (use -source 8 or higher to enable lambda expressions)
// Gradle
> Task :compileJava FAILED
/home/sparsick/dev/workspace/junit5-example/junit5-in-pre-java8-projects/src/main/java/ error: lambda expressions are not supported in -source 7
Function<String, String > java8Feature = (input) -> input;
(use -source 8 or higher to enable lambda expressions)
1 error

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':compileJava'.
> Compilation failed; see the compiler error output for details.

Now you can introduce JUnit 5 in your project and start writing test with JUnit 5.

<!-- Maven-->
<!-- junit-vintage-engine is needed for running elder JUnit4 test with JUnit5-->
// in Gradle
dependencies {
testCompile 'org.junit.jupiter:junit-jupiter-api:5.3.2'
testCompile 'org.junit.jupiter:junit-jupiter-engine:5.3.2'
testCompile 'org.junit.jupiter:junit-jupiter-params:5.3.2'
testCompile 'org.junit.vintage:junit-vintage-engine:5.3.2'

Your old JUnit 4 tests need not be migrated, because JUnit 5 has a test engine, that can run JUnit 4 tests with JUnit 5. So use JUnit 5 for new tests and only migrate JUnit 4 tests if you have to touch them anyway.

Although you can’t update your production code to a newer Java version, it has some benefit to update your test code to a newer one.

The biggest benefit is that you can start learning new language feature during your daily work when you write tests. You don’t make the beginner’s mistake in the production code. You have access to new tools that can help improve your tests. For example, in JUnit 5 it’s more comfortable to write parameterized tests than in JUnit 4. In my experience, developer writes rather parameterized test with JUnit 5 than with JUnit 4 in a situation where parameterized test make sense.

The above described technique also works for other Java version. For example, your production code is on Java 11 and you want to use Java 12 feature in your test code. Another use case for this technique could be learning another JVM language like Groovy, Kotlin or Clojure in your daily work. Then use the new language in your test code.

For Maven projects, this approach has one little pitfall. IntelliJ IDEA ignores the Java version configuration for test code. It uses the configured Java version in production code section for the whole project. An issue is already opened. A workaround is also described in this issue. So only the Maven build gives you the feedback if your production code uses correct Java version. IntelliJ hasn’t this problem for Gradle projects. Here, it uses the Java version just like it is configured in Gradle build file.

The situation in Netbeans looks better for Maven projects. Netbeans loads the Java configuration for Maven project, correctly. For Gradle projects, I couldn’t check it, because in Netbeans 10, there doesn’t yet exist a Gradle plugin (status: January 2019, but for Netbeans 9, so maybe something will come)


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How to Format a Large Code Base Automatically

If you introduce code formatting rules retroactively, you have to solve the problem how to format existing code base according to the new formatting rules. You could checkout every code repository one by one in your IDE and click on Autoformat the whole project. But this is boring and waste of time. Fortunately, Intellij IDEA has a format CLI tool in its installation. You can locate it in the path <your Intellij IDEA installation>/bin. It’s called

In the next section I’d like to show you how you can automate formatting big code base. First, I will show the preparation steps like exporting your code formatting rule setting from the IDE. Then, I will demonstrate how to use the CLI-Tool At the end, I will show a small Groovy script that query all repositories (in this case they are Git repositories), formatting the code and push it back to the remote SCM.


First at all, we need the code formatting rule setting exported from Intellij IDEA. In your Intellij IDEA follow the next step

  1. Open File -> Settings -Editor-> Code Style
  2. Click on Export…
  3. Choose a name for the XML file (for example, Default.xml) and a location where this file should be saved (for example, /home/foo ).

Then, checkout or clone your SCM repository and remember the location where you checkout/clone it (for example, /home/foo/myrepository).

Format Code Base Via  CLI Tool

Three parameters are important for

  • -s : Set a path to Intellij IDEA code style settings .xml file (in our example: /home/foo/Default.xml).
  • -r : Set that directories should be scanned recursively.
  • path<n> : Set a path to a file or a directory that should be formatted (in our example: /home/foo/myrepository).

> ./
IntelliJ IDEA 2018.2.4, build IC-182.4505.22 Formatter
Usage: format [-h] [-r|-R] [-s|-settings settingsPath] path1 path2...
-h|-help Show a help message and exit.
-s|-settings A path to Intellij IDEA code style settings .xml file.
-r|-R Scan directories recursively.
-m|-mask A comma-separated list of file masks.
path<n> A path to a file or a directory.

> / -r -s ~/Default.xml ~/myrepository

It’s possible that the tool cancels scanning because of a java.lang.OutOfMemoryError: Java heap space. Then, you have to increase Java’s maximum memory size (-Xmx) in <your Intellij IDEA installation>/bin/idea64.vmoptions.

> nano idea64.vmoptions
-Xmx750m // <- here increase the maximum memory size

Groovy Script For Formatting Many Repository In a Row

Now, we want to bring everything together. The script should do four things:

  1. Find all repository URLs whose code has to be formatted.
  2. Check out / Clone the repositories.
  3. Format the code in all branches of each repostory.
  4. Commit and push the change to the remote SCM.

I choose Git as SCM in my example. The finding of the repository URLs depends on the Git Management System (like BitBucket, Gitlab, SCM Manager etc.) that you use. But the approach is in all system the same:

  1. Call the RESTful API of your Git Management System.
  2. Parse the JSON object in the response after the URLs.

For example, in BitBucket it’s like that:


import static*
import static*

def cloneUrlsForProject() {

    def projectUrl = "https://scm/rest/api/1.0/projects/PROJECT_KEY/repos?limit=1000"
    def token = "BITBUCKET_TOKEN"

    def projects = []
    def cloneUrls = []

    def http = new HTTPBuilder(projectUrl)
    http.request(GET) {
        headers."Accept" = "application/json"
        headers."Authorization" = "Bearer ${token}"

        response.success = { resp -> projects = new JsonSlurper().parseText(resp.entity.content.text)}

        response.failure = { resp ->
            throw new RuntimeException("Error fetching clone urls for '${projectKey}': ${resp.statusLine}")

    projects.values.each { value ->
        def cloneLink = value.links.clone.find { == "ssh" }

    return cloneUrls

Then, we have to clone the repositories and checkout each branch. In each branch, the has to be called. For the git operation, we use the jgit library and for the call we use a Groovy feature for process calling. In Groovy it’s possible to define the command as a String and then to call the method execute() on this String like “ls -l”.execute(). So the Groovy script for the last three tasks would be looked like that:

#!/usr/bin/env groovy
import jgit.*
import org.eclipse.jgit.api.CreateBranchCommand
import org.eclipse.jgit.api.Git
import org.eclipse.jgit.api.ListBranchCommand
import org.eclipse.jgit.transport.UsernamePasswordCredentialsProvider

import java.nio.file.Files

def intellijHome = 'path to your idea home folder'
def codeFormatterSetting = 'path to your exported code formatter setting file'
def allRepositoriesUrls = ["http://scm/repo1","http://scm/repo2"] // for simplifying

allRepositoriesUrls.each { repository ->
    def repositoryName = repository.split('/').flatten().findAll { it != null }.last()
    File localPath = Files.createTempDirectory("${repositoryName}-").toFile()
    println "Clone ${repository} to ${localPath}"
       .setCredentialsProvider(new UsernamePasswordCredentialsProvider("user", "password")) // only needed when clone url is https / http
       .withCloseable { git ->
        def remoteBranches = git.branchList().setListMode(ListBranchCommand.ListMode.REMOTE).call()
        def remoteBranchNames = remoteBranches.collect {'refs/remotes/origin/', '') }

        println "Found the following branches: ${remoteBranchNames}"

        remoteBranchNames.each { remoteBranch ->
            println "Checkout branch $remoteBranch"
               .setStartPoint("origin/" + remoteBranch)

            def formatCommand = "$intellijHome/bin/ -r -s $codeFormatterSetting $localPath"

            println formatCommand.execute().text

               .setAuthor("Automator", "")
               .setMessage('Format code according to IntelliJ setting.')

            println "Commit successful!"

           .setCredentialsProvider(new UsernamePasswordCredentialsProvider("user", "password")) // only needed when clone url is https / http

        println "Push is done"


Do you have another approach? Let me know and write a comment below.