Is the container a requirement?

I want to know If the container is a requirement to develop applications with vaadin.

If you mean a Servlet container then yes, you need one (Tomcat, Jetty) or an Application server like JBoss.
Vaadin is mainly a server side framework so you can write your application in java and avoid marshalling/unmarshalling data to/from the browser.
If you need a client-only framework and don’t like javascript you can use GWT (Vaadin is built on GWT).

If you mean the Container interface (a tabular view of data) you will need it too, since many Vaadin components (Table, Tree, Combobox, …) use it.

Thanks for your answer, Claudio.
I meant the container interface. I thought I could put the data directly to a table without using the container. Thought that the container was optional.