Grails is one of the best web frameworks for Java platform. It aimed at multiplying developers productivity with features such as Convention-over-Configuration, sensible defaults, and opinionated APIs. It also easily integrates smoothly with the JVM.
Spring MVC offers a wide range of services: API REST, SOAP web services, security, etc. Most of the developer community is working with spring and therefore there is a massive source of documentation.
JSF is very easy to use because there is a lot of documentation provided by Oracle. It has many features, such as libraries and tools (including a set of tools for creating user-friendly interfaces).
Vaadin is main and most popular for business application development. Using a well-known component approach, it can simplify the web application development by availing UI designer, data visualization tools, and components provided by the web framework.
GWT is a free Java framework that allows programmers to create and optimize sophisticated web-based applications. It provides Java APIs and basic widgets for building compiled applications which can be later applied to JavaScript.