Implementation:SeleniumHQ Selenium DevTools Event

Knowledge Sources	SeleniumHQ_Selenium Selenium Documentation
Domains	WebDriver, DevTools_Protocol
Last Updated	2026-02-12 00:00 GMT

Overview

The Event class is a generic container representing a Chrome DevTools Protocol event, encapsulating the event method name and a mapper function to deserialize event payloads.

Description

Event<X> models a CDP event that can be listened for through a DevTools session. Each event carries a method name (e.g., "Network.requestWillBeSent") and a Function<JsonInput, X> mapper that deserializes the incoming JSON event payload into the expected type X. The class provides a toString() override that returns the method name, making it convenient for logging and debugging purposes.

Usage

Use Event when subscribing to CDP events through a DevTools session. Like Command, events are typically instantiated by auto-generated CDP domain classes (e.g., Network.requestWillBeSent()), but can be constructed directly for custom or experimental CDP events.

Code Reference

Source Location

• Repository: SeleniumHQ_Selenium
• File: java/src/org/openqa/selenium/devtools/Event.java

Signature

public class Event<X> {

  public Event(String method, Function<JsonInput, X> mapper)

  public String getMethod()
  public String toString()
}

Import

import org.openqa.selenium.devtools.Event;

I/O Contract

Constructor Parameters

Parameter	Type	Required	Description
method	String	Yes	The CDP event method name (e.g., "Network.requestWillBeSent")
mapper	Function<JsonInput, X>	Yes	Function to deserialize the JSON event payload into type X

Return Values

Method	Return Type	Description
getMethod()	String	The CDP event method name
toString()	String	Returns the event method name (useful for logging)

Internal Access

Method	Return Type	Visibility	Description
getMapper()	Function<JsonInput, X>	Package-private	The mapper function used internally by the DevTools session to deserialize event data

Usage Examples

// Subscribing to a CDP event via the DevTools session
DevTools devTools = ((HasDevTools) driver).getDevTools();
devTools.createSession();

// Using auto-generated domain events (typical usage)
devTools.addListener(Network.requestWillBeSent(), requestWillBeSent -> {
    System.out.println("Request URL: " + requestWillBeSent.getRequest().getUrl());
});

// Creating a custom event manually
Event<Map<String, Object>> customEvent = new Event<>(
    "Runtime.consoleAPICalled",
    input -> input.read(new TypeToken<Map<String, Object>>(){}.getType())
);
devTools.addListener(customEvent, data -> {
    System.out.println("Console event: " + data);
});

Related Pages

• DevTools Command -- companion class for sending CDP commands
• DevTools ConverterFunctions -- utility functions for building event mappers
• Observer Pattern -- events follow a publish-subscribe model via addListener
• Type Safety -- generic type parameter ensures event payloads are deserialized to the correct type