Implementation:SeleniumHQ Selenium Bootstrap Main Entry

Knowledge Sources	Selenium
Domains	Distributed_Testing, Process_Management, Selenium_Grid
Last Updated	2026-02-11 00:00 GMT

Overview

Concrete tool for bootstrapping Selenium Grid from the command line provided by the Bootstrap and Main classes.

Description

Bootstrap is the JVM entry point (public static void main(String[] args)). It parses --ext flags for extension JAR paths (using File.pathSeparator as delimiter), creates a URLClassLoader with those JARs, wraps it in a custom PossessiveClassLoader (child-first classloader that only delegates java.*, javax.*, sun.*, and jdk.* prefixes to the parent), sets it as the thread context classloader, then reflectively loads and invokes Main.main(). Main uses ServiceLoader to discover all CliCommand implementations sorted by name via a TreeSet, matches args[0] to a command name using parallelStream().filter(), and calls command.configure(out, err, remainingArgs).run(). If no command matches, a built-in Help command displays all registered commands.

Usage

Invoked when running java -jar selenium-server.jar <command>. The first argument determines which Grid component starts.

Code Reference

Source Location

• Repository: Selenium
• File: java/src/org/openqa/selenium/grid/Bootstrap.java (L39-181)
• File: java/src/org/openqa/selenium/grid/Main.java (L34-157)

Signature

public class Bootstrap {
    public static void main(String[] args);
    // Handles --ext for extensions via PossessiveClassLoader
    // Delegates to Main.main(args) via reflection
}

public class Main {
    public static void main(String[] args);
    Main(PrintStream out, PrintStream err, String[] args);
    void go();
    // Discovers CliCommand implementations via ServiceLoader
    // Matches args[0] to command name
    // Falls back to Help command if no match
}

Import

// Entry point classes - not directly imported by user code
// Invoked via: java -jar selenium-server.jar <command> [args]

I/O Contract

Inputs

Name	Type	Required	Description
args[0]	String	No	Command name: standalone, hub, node, distributor, router, sessions, sessionqueue. If omitted, displays help.
--ext	String	No	File.pathSeparator-separated extension JAR paths or directories. Must be first argument if present.
remaining args	String[]	No	Forwarded to the selected command's configure() method

Outputs

Name	Type	Description
Running Grid	HTTP Server	Grid component running on configured port
Help output	Text (stdout)	List of available commands with descriptions (if no command specified)

Usage Examples

# Standard standalone
java -jar selenium-server.jar standalone

# With extensions (colon-separated on Linux, semicolon on Windows)
java -jar selenium-server.jar --ext /path/to/extensions:/path/to/plugin.jar standalone --port 4444

# Help for a specific command
java -jar selenium-server.jar standalone --help

# List all available commands
java -jar selenium-server.jar

Related Pages

Implements Principle

• Principle:SeleniumHQ_Selenium_Grid_Bootstrap_Process

Requires Environment

• Environment:SeleniumHQ_Selenium_Grid_Deployment_Environment