How can I communicate two DOCKER containers (a WEB application (java ee) with a SQL database)

Docker Engine Compose
1

I am a beginner in DevOps,
I have to connect a local application (javaee) with a mysql container, but when I put this application on a container, I can not get them to communicate

2

try to not combine multiple applications within one container.
use the official mysql image.
use an image of your java software.

start the mysql image. then start your image and link it to the mysql container. then your app can reach the mysql server under the hostname mysql