When one tries to migrate her project to a newer version of a framework, it usually helps if the transition is smooth and the original code works without any modifications. This way, you can convert the code to the new API gradually, and never encounter this OMG-shit-doesn't-compile-everybody-blocked period for a long time.
Migration from Vaadin 7 to Vaadin 8 isn't as straightforward since some modifications to Java source files are required, but the guide of migrating to Vaadin 8 may assist you well in converting your imports from Vaadin 7's
com.vaadin.ui.* components to their Vaadin 8's compatibility counterparts in the
Unfortunately the actual problem lies with Add-ons since they depend on
com.vaadin.ui.* components and need to be modified as well. For example all
Container-based addons need to import
com.vaadin.v7.data.Container instead of
com.vaadin.data.Container - a small change indeed, but will cause the addon to malfunction in runtime.
Luckily, the change is straightforward. I have converted the JPAContainer 3.2.0 to be compatible with Vaadin 8 and thus to be compatible with the
com.vaadin.v7.ui.Grid. This will allow you to gradually convert your Grids to v8 Grids and the old Container-based code to the
EDIT: the changes have been merged to the official JPAContainer Add-on, so just use JPAContainer 4.0.0 with Vaadin 8: https://vaadin.com/directory#!addon/vaadin-jpacontainer