What is the difference between JerseyServletModule and ServletModule?

Question

I am trying to understand what is the difference between JerseyServletModule present in jersey-guice library and ServletModulepresent in Guice library.

Answer 1

TL;DR - JerseyServletModule is dead. It used to (in the Jersey 1 days) allow you to use Jersey and Guice and have them play nice. That's no longer simple.

ServletModule is a Guice module which allows you to configure servlets, servlet mappings, filters and filter mappings (amongst other things) using Guice as well as inject objects into your servlets. Create a class which inherits from ServletModule and override the configureServlets method a bit like this:

class MyModule extends ServletModule {

    @Override
    protected void configureServlets() {
        serve("/hello").with(HelloAppEngine.class);
    }
}

The documentation for building webservices with Guice and ServletModule is here.

Jersey is an implementation of of the JSR 370 so called JAX-RS API for creating rest services. It allows you to build rest services with little more than annotated classes - for example:

@Path("/user")
public class UserController {

    UserPersistService userPersistService;

    ObjectMapper objectMapper;

    UserController(UserPersistService userPersistService, ObjectMapper objectMapper) {
        this.userPersistService = userPersistService;
        this.objectMapper = objectMapper;
    }

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public String getUsersAsJSON() throws IOException {
        final List<User> users = userPersistService.getUsers();
        return objectMapper.writeValueAsString(users);
    }
}

In the old days of Jersey 1.0, overriding JerseyServletModule instead of Servlet Module would permit you to do both at the same time, so the above class could become:

@Singleton
@Path("/user")
public class UserController {

    @Inject
    UserPersistService userPersistService;

    @Inject
    ObjectMapper objectMapper;

    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public String getUsersAsJSON() throws IOException {
        final List<User> users = userPersistService.getUsers();
        return objectMapper.writeValueAsString(users);
    }

However as I alluded in the opening, there is no equivalent of JerseyServletModule in Jersey 2.0. Your options are to configure an HK-Guice bridge and continue with Jersey, or to use RestEasy which is an alternative JAX-RS implementation which does play nicely with guice.