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We build and test Apache Kafka with Java 8, 11 and 17. We set the release parameter in javac and scalac
to 8 to ensure the generated binaries are compatible with Java 8 or higher (independently of the Java version
used for compilation). Java 8 support has been deprecated since Apache Kafka 3.0 and will be removed in Apache
Kafka 4.0 (see KIP-750 for more details).
Scala 2.12 and 2.13 are supported and 2.13 is used by default. Scala 2.12 support has been deprecated since
Apache Kafka 3.0 and will be removed in Apache Kafka 4.0 (see KIP-751
for more details). See below for how to use a specific Scala version or all of the supported Scala versions.
./gradlew javadoc
./gradlew javadocJar # builds a javadoc jar for each module
./gradlew scaladoc
./gradlew scaladocJar # builds a scaladoc jar for each module
./gradlew docsJar # builds both (if applicable) javadoc and scaladoc jars for each module
Run unit/integration tests
./gradlew test # runs both unit and integration tests
./gradlew unitTest
./gradlew integrationTest
Force re-running tests without code change
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div class="snippet-clipboard-content notranslate position-relative overflow-auto" data-snippet-clipboard-copy-content="./gradlew -Prerun-tests test
./gradlew -Prerun-tests unitTest
./gradlew -Prerun-tests integrationTest">
./gradlew -Prerun-tests test
./gradlew -Prerun-tests unitTest
./gradlew -Prerun-tests integrationTest
By default, each failed test is retried once up to a maximum of five retries per test run. Tests are retried at the end of the test task. Adjust these parameters in the following way:
./gradlew test -PmaxTestRetries=1 -PmaxTestRetryFailures=5
The release file can be found inside ./core/build/distributions/.
Building auto generated messages
Sometimes it is only necessary to rebuild the RPC auto-generated message data when switching between branches, as they could
fail due to code changes. You can just run:
Running a task with one of the Scala versions available (2.12.x or 2.13.x)
Note that if building the jars with a version other than 2.13.x, you need to set the SCALA_VERSION variable or change it in bin/kafka-run-class.sh to run the quick start.
You can pass either the major version (eg 2.12) or the full version (eg 2.12.7):
./gradlew -PscalaVersion=2.12 jar
./gradlew -PscalaVersion=2.12 test
./gradlew -PscalaVersion=2.12 releaseTarGz
Running a task with all the scala versions enabled by default
Invoke the gradlewAll script followed by the task(s):
./gradlewAll test
./gradlewAll jar
./gradlewAll releaseTarGz
Running a task for a specific project
This is for core, examples and clients
./gradlew core:jar
./gradlew core:test
Streams has multiple sub-projects, but you can run all the tests:
./gradlew :streams:testAll
Listing all gradle tasks
./gradlew tasks
Building IDE project
Note that this is not strictly necessary (IntelliJ IDEA has good built-in support for Gradle projects, for example).
./gradlew eclipse
./gradlew idea
The eclipse task has been configured to use ${project_dir}/build_eclipse as Eclipse's build directory. Eclipse's default
build directory (${project_dir}/bin) clashes with Kafka's scripts directory and we don't use Gradle's build directory
to avoid known issues with this configuration.
Publishing the jar for all versions of Scala and for all projects to maven
The recommended command is:
./gradlewAll publish
For backwards compatibility, the following also works:
./gradlewAll uploadArchives
Please note for this to work you should create/update ${GRADLE_USER_HOME}/gradle.properties (typically, ~/.gradle/gradle.properties) and assign the following variables
Publishing the streams quickstart archetype artifact to maven
For the Streams archetype project, one cannot use gradle to upload to maven; instead the mvn deploy command needs to be called at the quickstart folder:
cd streams/quickstart
mvn deploy
Please note for this to work you should create/update user maven settings (typically, ${USER_HOME}/.m2/settings.xml) to assign the following variables
There are two code quality analysis tools that we regularly run, spotbugs and checkstyle.
Checkstyle
Checkstyle enforces a consistent coding style in Kafka.
You can run checkstyle using:
./gradlew checkstyleMain checkstyleTest
The checkstyle warnings will be found in reports/checkstyle/reports/main.html and reports/checkstyle/reports/test.html files in the
subproject build directories. They are also printed to the console. The build will fail if Checkstyle fails.
Spotbugs
Spotbugs uses static analysis to look for bugs in the code.
You can run spotbugs using:
./gradlew spotbugsMain spotbugsTest -x test
The spotbugs warnings will be found in reports/spotbugs/main.html and reports/spotbugs/test.html files in the subproject build
directories. Use -PxmlSpotBugsReport=true to generate an XML report instead of an HTML one.
JMH microbenchmarks
We use JMH to write microbenchmarks that produce reliable results in the JVM.
The following options should be set with a -P switch, for example ./gradlew -PmaxParallelForks=1 test.
commitId: sets the build commit ID as .git/HEAD might not be correct if there are local commits added for build purposes.
mavenUrl: sets the URL of the maven deployment repository (file://path/to/repo can be used to point to a local repository).
maxParallelForks: maximum number of test processes to start in parallel. Defaults to the number of processors available to the JVM.
maxScalacThreads: maximum number of worker threads for the scalac backend. Defaults to the lowest of 8 and the number of processors
available to the JVM. The value must be between 1 and 16 (inclusive).
ignoreFailures: ignore test failures from junit
showStandardStreams: shows standard out and standard error of the test JVM(s) on the console.
skipSigning: skips signing of artifacts.
testLoggingEvents: unit test events to be logged, separated by comma. For example ./gradlew -PtestLoggingEvents=started,passed,skipped,failed test.
xmlSpotBugsReport: enable XML reports for spotBugs. This also disables HTML reports as only one can be enabled at a time.
maxTestRetries: maximum number of retries for a failing test case.
maxTestRetryFailures: maximum number of test failures before retrying is disabled for subsequent tests.
enableTestCoverage: enables test coverage plugins and tasks, including bytecode enhancement of classes required to track said
coverage. Note that this introduces some overhead when running tests and hence why it's disabled by default (the overhead
varies, but 15-20% is a reasonable estimate).
scalaOptimizerMode: configures the optimizing behavior of the scala compiler, the value should be one of none, method, inline-kafka or
inline-scala (the default is inline-kafka). none is the scala compiler default, which only eliminates unreachable code. method also
includes method-local optimizations. inline-kafka adds inlining of methods within the kafka packages. Finally, inline-scala also
includes inlining of methods within the scala library (which avoids lambda allocations for methods like Option.exists). inline-scala is
only safe if the Scala library version is the same at compile time and runtime. Since we cannot guarantee this for all cases (for example, users
may depend on the kafka jar for integration tests where they may include a scala library with a different version), we don't enable it by
default. See https://www.lightbend.com/blog/scala-inliner-optimizer for more details.
Dependency Analysis
The gradle dependency debugging documentation mentions using the dependencies or dependencyInsight tasks to debug dependencies for the root project or individual subprojects.
Alternatively, use the allDeps or allDepInsight tasks for recursively iterating through all subprojects: