# Build a Chat Room Application with Redpanda Cloud and Java > For the complete documentation index, see [llms.txt](https://docs.redpanda.com/llms.txt). Component-specific: [labs-full.txt](https://docs.redpanda.com/labs-full.txt) --- title: Build a Chat Room Application with Redpanda Cloud and Java latest-operator-version: v26.1.4 latest-console-tag: v3.7.3 latest-connect-version: 4.93.0 latest-redpanda-tag: v26.1.9 docname: cloud-java page-component-name: labs page-version: master page-component-version: master page-component-title: Labs page-relative-src-path: cloud-java.adoc page-edit-url: https://github.com/redpanda-data/redpanda-labs/edit/main/docs/modules/clients/pages/cloud-java.adoc description: Create a basic chat room application with Redpanda Cloud and Kafka Java clients. page-git-created-date: "2025-05-06" page-git-modified-date: "2025-05-06" --- Create a basic chat room application with Redpanda Cloud and [Kafka Java clients](https://central.sonatype.com/artifact/org.apache.kafka/kafka-clients). This example shows you how to: - Write a client application in Java to produce and consume chat room messages. - Build and run multiple clients to exchange chat messages streamed through Redpanda Cloud. ![Demo of the application](https://docs.redpanda.com/labs/clients/_images/chat-room.gif) ## [](#what-is-a-chat-room-application)What is a chat room application? A chat room application is software that enables users to engage in real-time textual communication with one another. These applications typically allow multiple users to join a chat room, where they can send messages and interact with others in a group conversation. Chat room applications often include features such as private messaging, user profiles, and notifications. Some popular chat room applications include Slack, Discord, and WhatsApp. ## [](#why-use-redpanda)Why use Redpanda? Redpanda offers several features that make it ideal for building a fast, scalable, and robust chat room application. - Scalability: Redpanda can scale horizontally and vertically to accommodate growing chat room usage over time. - Low-latency: Redpanda is designed for minimal latency to provide a smooth user experience and fast message delivery. - Fault tolerance: Redpanda is resilient to failures, thanks to its built-in replication and partitioning capabilities. This built-in resilience ensures that the chat room application continues to serve users even if individual brokers in the cluster experience downtime. - Durability: Redpanda persists messages on disk, maintaining chat history and allowing users to read previous conversations. ## [](#prerequisites)Prerequisites - Complete the [Redpanda Cloud Quickstart](https://docs.redpanda.com/current/get-started/quick-start-cloud/) before continuing. This example expands on the quickstart. - Install the following: - Java 11 or 17 (OpenJDK is recommended) - Maven ### Windows/Linux You can download OpenJDK from [Adoptium](https://adoptium.net/temurin/releases), and can follow the installation instructions for Maven on the [official Maven website](https://maven.apache.org/install.html). ### macOS Mac users with Homebrew installed can run the following commands to install these dependencies: ```bash brew install openjdk@11 maven ``` Make sure to follow any symlinking instructions in the Caveats output. When the prerequisites are installed, the following commands should print the version of both Java and Maven: ```bash java --version mvn --version ``` > 📝 **NOTE** > > Redpanda Cloud uses TLS certificates signed by [Let’s Encrypt](https://letsencrypt.org/). Most programming languages will load their root certificate authority (CA), `ISRG Root X1`, by default so you shouldn’t need to provide a custom CA certificate. ## [](#run-the-lab)Run the lab Compile the client chat application, run it from multiple client terminals, and chat between the clients. 1. Clone this repository: ```bash git clone https://github.com/redpanda-data/redpanda-labs.git ``` 2. Change into the example directory: ```bash cd clients/chat-room/cloud/java ``` 3. Open the Java files and replace the placeholders wrapped in angle brackets (`<>`) with the same values that you used in the Redpanda Cloud Quickstart. 4. Install the dependencies by building the project: ```bash mvn package ``` The output is verbose, but you should see a successful build message: \[INFO\] BUILD SUCCESS 5. Verify that the `chat-room` topic exists in your cluster by listing all topics: ```bash rpk topic list --tls-enabled ``` Output: NAME PARTITIONS REPLICAS chat-room 1 1 6. If the topic doesn’t exist yet, use [`rpk`](https://docs.redpanda.com/current/get-started/rpk/) to create a `chat-room` topic: ```bash rpk topic create chat-room --tls-enabled ``` Output: TOPIC STATUS chat-room OK 7. From `chat-room/cloud/java`, compile the client application: ```bash mvn compile ``` 8. Open at least two terminals, and for each terminal: 1. Run the client application: ```bash mvn exec:java -Dexec.mainClass="com.example.Main" ``` 2. When prompted with `Enter user name:`, enter a unique name for the chat room. 9. Use the chat application: enter a message in a terminal, and verify that the message is received in the other terminals. For example: Enter user name: Alice Connected, press Ctrl+C to exit Alice: Hi, I'm Alice Bob: Hi Alice, I'm Bob, nice to meet you ## [](#files-in-the-example)Files in the example This example includes the following files: - [`src/main/java/com/example/Admin.java`](https://github.com/redpanda-data/redpanda-labs/blob/main/clients/chat-room/cloud/java/src/main/java/com/example/Admin.java): Checks whether the `chat-room` topic exists and creates it if not. - [`src/main/java/com/example/ChatProducer.java`](https://github.com/redpanda-data/redpanda-labs/blob/main/clients/chat-room/cloud/java/src/main/java/com/example/ChatProducer.java): A producer that sends strings entered by the user of the terminal to the `chat-room` topic. Messages are sent as JSON encoded strings. - [`src/main/java/com/example/ChatConsumer.java`](https://github.com/redpanda-data/redpanda-labs/blob/main/clients/chat-room/cloud/java/src/main/java/com/example/ChatConsumer.java): A consumer that reads all messages from the `chat-room` topic and prints them to the console. You can start as many consumer groups as you like, but each group reads a message only once, which is why the example is using a generated UUID for the group ID. This way, each time you run the application, you see all previous messages. - [`src/main/java/com/example/Main.java`](https://github.com/redpanda-data/redpanda-labs/blob/main/clients/chat-room/cloud/java/src/main/java/com/example/Main.java): The client application that creates the topic, producer, and consumer and implements the chat logic. ## [](#next-steps)Next steps This is a basic example of a chat room application. You can improve this application by implementing additional features and components, such as: - A user interface to make it more interactive and user-friendly. - A user registration and login system to authenticate users before they can access the chat room. - Rate limiting and other measures to prevent spamming and abuse in the chat room. ## [](#suggested-reading)Suggested reading For additional resources to help you build stream processing applications that can aggregate, join, and filter your data streams, see: - [Redpanda University](https://university.redpanda.com/) - [Redpanda Blog](https://redpanda.com/blog) - [Resources](https://redpanda.com/resources)