Unable to connect to mysql using jdbc in docker

I have the following docker-compose:

version: '3.1'
services:
  db:
    container_name: db
    image: mysql
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_DATABASE=world
    volumes:
      - ./mysql-db/:/docker-entrypoint-initdb.d
    networks:
      - my-network
  app:
    depends_on:
      - db
    container_name: app
    build: App/
    networks:
      - my-network
networks:
  my-network:
    driver: bridge

This builds the mysql image and uses a local file to create the database. I am able to connect to the database through a database client on my host machine. I know the db is running and working with those credentials on port 3306.

App/Dockerfile:

# Build stage
FROM maven:latest AS build
COPY src /app/src
COPY pom.xml /app
# need to assemble to package in plugins
RUN mvn -f /app/pom.xml clean compile assembly:single

# Package stage
FROM openjdk:latest
COPY --from=build /app/target/seMethods-1.0-jar-with-dependencies.jar /usr/local/lib/build.jar
ENTRYPOINT ["java", "-jar", "/usr/local/lib/build.jar"]

This builds the jar file using maven.

App/src/App.java

// sql imports
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;

public class App 
{
  public static void main( String[] args )
  {
    try {
      String dbUrl = "jdbc:mysql://db:3306/world";
      Connection con = DriverManager.getConnection(dbUrl,"root","password");

      String testStatement = "SELECT * FROM city;";
      PreparedStatement preparedTest = con.prepareStatement(testStatement);
      ResultSet rs = preparedTest.executeQuery();

      while(rs.next()){
        System.out.println(rs.getRow());
      }

    } catch (Exception e) {
      // handle any errors
      System.out.println(String.format("Error: %s", e));
    }
  }
}

When my docker-compose runs, the containers are created although my app stops with the following:

Error: com.mysql.cj.jdbc.exceptions.CommunicationsException: Communications link failure

The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server.

How can I connect my db container to app?