Create the Maven POM file

Create an empty directory to store your Maven project. Inside of that directory create the pom.xml file with the content as below.

<?xml version="1.0" encoding="UTF-8"?>

<project
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>cloud.piranha.guides.servlet</groupId>
    <artifactId>websocket</artifactId>
    <version>24.11.0-SNAPSHOT</version>
    <packaging>war</packaging>
    <name>Piranha Servlet - WebSocket Chat application</name>
    <properties>
        <jakarta.websocket.version>2.1.0</jakarta.websocket.version>
        <java.version>17</java.version>
        <maven-compiler-plugin.version>3.11.0</maven-compiler-plugin.version>
        <maven-war-plugin.version>3.3.2</maven-war-plugin.version>
        <piranha.distribution>servlet</piranha.distribution>
        <piranha.version>23.6.0</piranha.version>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    </properties>
    <dependencies>
        <dependency>
            <groupId>jakarta.websocket</groupId>
            <artifactId>jakarta.websocket-api</artifactId>
            <version>${jakarta.websocket.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>jakarta.websocket</groupId>
            <artifactId>jakarta.websocket-client-api</artifactId>
            <version>${jakarta.websocket.version}</version>
            <scope>provided</scope>
        </dependency>
    </dependencies>
    <build>
        <finalName>websocket</finalName>
        <plugins>
            <plugin>
                <groupId>cloud.piranha.maven.plugins</groupId>
                <artifactId>piranha-maven-plugin</artifactId>
                <version>${piranha.version}</version>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <release>${java.version}</release>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>${maven-war-plugin.version}</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

Add the ChatEndpoint.java file

Add the ChatEndpoint.java file in the src/main/java/chat directory.

package chat;

import jakarta.websocket.OnMessage;
import jakarta.websocket.Session;
import jakarta.websocket.server.ServerEndpoint;

@ServerEndpoint("/chat")
public class ChatEndpoint {

     @OnMessage
     public String onMessage(String message, Session session) {
         return message;
     }
}

Deploy the application

To deploy your application you will need 2 pieces.

1. The Piranha Servlet runtime JAR.
2. The WAR file you just produced.

For the WAR file see the target directory. For the Piranha Servlet distribution go to Maven Central. And then the following command line will deploy your application:

  java -jar piranha-dist-servlet.jar --war-file websocket.war

Test the application

To test the application connect to ws://localhost:8080/websocket/chat using a WebSocket client.

Conclusion

As you can creating a WebSocket application using Piranha Servlet is quite easy!