Tomcat is a servlet container and therefore does not provide some of the required JEE libraries out-of-the-box.

My basic set-up of a REST-based server, just as a demo (and no frameworks!), uses Java 15 with Tomcat 10.

The Maven POM:

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<?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>org.ajames</groupId>
    <artifactId>JaxRsDemo</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <name>JaxRsDemo</name>

    <properties>
        <endorsed.dir>${project.build.directory}/endorsed</endorsed.dir>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>15</maven.compiler.source>
        <maven.compiler.target>15</maven.compiler.target>
    </properties>

    <dependencies>

        <!-- the REST API -->
        <dependency>
            <groupId>jakarta.ws.rs</groupId>
            <artifactId>jakarta.ws.rs-api</artifactId>
            <version>3.0.0</version>
        </dependency>

        <!-- These next two are needed because we are using Tomcat, which  -->
        <!-- is not a full JEE server - it's just a servlet container.     -->

        <!-- the Jersey implementation -->
        <dependency>
            <groupId>org.glassfish.jersey.containers</groupId>
            <artifactId>jersey-container-servlet</artifactId>
            <version>3.0.2</version>
        </dependency>

        <!-- also needed for dependency injection -->
        <dependency>
            <groupId>org.glassfish.jersey.inject</groupId>
            <artifactId>jersey-hk2</artifactId>
            <version>3.0.2</version>
        </dependency>

        <!-- support for using Jackson (JSON) with Jersey -->
        <dependency>
            <groupId>org.glassfish.jersey.media</groupId>
            <artifactId>jersey-media-json-jackson</artifactId>
            <version>3.0.2</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>15</source>
                    <target>15</target>
                    <compilerArguments>
                        <endorseddirs>${endorsed.dir}</endorseddirs>
                    </compilerArguments>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>3.3.1</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-dependency-plugin</artifactId>
                <version>3.1.2</version>
                <executions>
                    <execution>
                        <phase>validate</phase>
                        <goals>
                            <goal>copy</goal>
                        </goals>
                        <configuration>
                            <outputDirectory>${endorsed.dir}</outputDirectory>
                            <silent>true</silent>
                            <artifactItems>
                                <artifactItem>
                                    <groupId>javax</groupId>
                                    <artifactId>javaee-endorsed-api</artifactId>
                                    <version>7.0</version>
                                    <type>jar</type>
                                </artifactItem>
                            </artifactItems>
                        </configuration>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>


</project>

There is no web.xml needed - we use annotations instead.

For the main entry point:

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import jakarta.ws.rs.ApplicationPath;
import jakarta.ws.rs.core.Application;

@ApplicationPath("api")
public class App extends Application {
    // the entry class - deliberately empty in this basic demo
}

A demo resource:

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import jakarta.ws.rs.Consumes;
import jakarta.ws.rs.GET;
import jakarta.ws.rs.POST;
import jakarta.ws.rs.Path;
import jakarta.ws.rs.PathParam;
import jakarta.ws.rs.Produces;
import jakarta.ws.rs.core.MediaType;
import jakarta.ws.rs.core.Response;

//
// Pingable at:
// http://localhost:8080/JaxRsDemo/api/demo/ping
//
@Path("/demo")
public class DemoResource {

    @GET
    @Path("/ping")
    public Response ping() {
        return Response.ok().entity("Service online").build();
    }

    @GET
    @Path("/get/{id}")
    @Produces(MediaType.APPLICATION_JSON)
    public Response getNotification(@PathParam("id") int id) {
        return Response.ok()
                .entity(new DemoPojo(id, "test message"))
                .build();
    }

    @POST
    @Path("/post/")
    @Consumes(MediaType.APPLICATION_JSON)
    @Produces(MediaType.APPLICATION_JSON)
    public Response postNotification(DemoPojo notification) {
        return Response.status(201).entity(notification).build();
    }
}

The POJO:

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public class DemoPojo {

    private int id;
    private String message;

    public DemoPojo() {
    }

    public DemoPojo(int id, String message) {
        this.id = id;
        this.message = message;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getMessage() {
        return message;
    }

    public void setMessage(String message) {
        this.message = message;
    }

}

Acknowledgement: The above is adapted and updated from the example here.