Implementation:Apache Kafka Kafka Run Class Classpath

Knowledge Sources	Apache Kafka
Domains	Operations, JVM_Configuration
Last Updated	2026-02-09 12:00 GMT

Overview

Concrete tool for constructing the JVM classpath from Kafka's modular build directories provided by kafka-run-class.sh.

Description

The classpath assembly section of kafka-run-class.sh constructs the CLASSPATH environment variable by scanning multiple module directories. It uses a should_include_file function to filter out test, source, and javadoc JARs. The default Scala version is read from gradle.properties and can be overridden via the SCALA_VERSION environment variable.

Usage

This is an internal section of kafka-run-class.sh and is not invoked directly. It runs automatically when any Kafka script delegates to the run-class launcher. Override CLASSPATH to provide a custom classpath, or set INCLUDE_TEST_JARS=true for testing.

Code Reference

Source Location

• Repository: Apache Kafka
• File: bin/kafka-run-class.sh
• Lines: L49-198

Signature

# Function to filter JAR files
should_include_file() {
    # Excludes: *-test.jar, *-sources.jar, *-javadoc.jar
    # Includes test JARs only if INCLUDE_TEST_JARS=true
}

# Environment variables:
# SCALA_VERSION    - Scala version (default: read from gradle.properties, e.g. 2.13.18)
# INCLUDE_TEST_JARS - Include test JARs (default: false)
# CLASSPATH        - Resulting classpath (output)

# Scanned directories:
# $base_dir/core/build/libs/, $base_dir/core/build/dependant-libs-${SCALA_VERSION}/
# $base_dir/clients/build/libs/, $base_dir/streams/build/libs/
# $base_dir/tools/build/libs/, $base_dir/connect/*/build/libs/
# $base_dir/libs/ (release layout)

Import

# Automatically invoked by kafka-run-class.sh
# Override: export CLASSPATH="/custom/path/*"

I/O Contract

Inputs

Name	Type	Required	Description
SCALA_VERSION	env	No	Scala version for JAR selection (default from gradle.properties)
INCLUDE_TEST_JARS	env	No	Include test JARs in classpath (default: false)
base_dir	computed	Yes	Kafka installation root directory

Outputs

Name	Type	Description
CLASSPATH	env	Colon-separated list of all required JAR paths

Usage Examples

Default Classpath Assembly

# Normal operation (automatic via kafka-server-start.sh)
bin/kafka-server-start.sh config/server.properties
# CLASSPATH is assembled internally

# Override Scala version
export SCALA_VERSION=2.13.18
bin/kafka-run-class.sh kafka.Kafka config/server.properties

# Include test JARs for testing
export INCLUDE_TEST_JARS=true
bin/kafka-run-class.sh kafka.tools.TopicCommand --list

Related Pages

Implements Principle

• Principle:Apache_Kafka_JVM_Classpath_Assembly
• Environment:Apache_Kafka_JVM_Runtime_Environment