java.lang.NoClassDefFoundError: org/hsqldb/jdbc/JDBCPool

Assim que terminei a carreira de Java WEB fui por em prática os conceitos que aprendi. E ao tentar criar o CRUD para minha aplicação WEB me deparei com um comportamento estranho. Não consigo abrir uma conexão com o banco HSQLDB através de uma servlet, porém se uso uma classe com um main a conexão funciona normalmente. Detalhes abaixo.

codigo da Servlet:

package br.com.jsantos.aboutmepage.web;

import java.io.IOException;
import java.sql.Connection;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import br.com.jsantos.aboutmepage.dao.ConnectionPool;

@WebServlet(urlPatterns = "/acess")
public class Acess extends HttpServlet{

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        try(Connection con = new ConnectionPool().getConnection()){
            System.out.println("Conexão criada com sucesso!");
        } catch (SQLException e) {
            e.printStackTrace();
        }
    }
}

codigo do ConnectionPool:

package br.com.jsantos.aboutmepage.dao;

import java.sql.Connection;
import java.sql.SQLException;

import javax.sql.DataSource;

import org.hsqldb.jdbc.JDBCPool;

public class ConnectionPool {

    private DataSource dataSource;

    public ConnectionPool() {

        JDBCPool pool = new JDBCPool();
        pool.setUrl("jdbc:hsqldb:hsql://localhost/new-db");
        pool.setUser("SA");
        pool.setPassword("");
        this.dataSource = pool;
    }

    public Connection getConnection() throws SQLException {
        Connection connection = dataSource.getConnection();
        return connection;
    }



}

Erro ao executar a Servlet - HTTP Status 500 - Servlet execution threw an exception:

type Exception report

message Servlet execution threw an exception

description The server encountered an internal error that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: Servlet execution threw an exception
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.NoClassDefFoundError: org/hsqldb/jdbc/JDBCPool
    br.com.jsantos.aboutmepage.dao.ConnectionPool.<init>(ConnectionPool.java:16)
    br.com.jsantos.aboutmepage.web.Acess.doPost(Acess.java:24)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
root cause

java.lang.ClassNotFoundException: org.hsqldb.jdbc.JDBCPool
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1858)
    org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1701)
    br.com.jsantos.aboutmepage.dao.ConnectionPool.<init>(ConnectionPool.java:16)
    br.com.jsantos.aboutmepage.web.Acess.doPost(Acess.java:24)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:650)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:731)
    org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
note The full stack trace of the root cause is available in the Apache Tomcat/7.0.68 logs.