Difference between RESTEasy and JAX-RS

According to its homepage RESTEasy is

... a fully certified and portable implementation of the JAX-RS specification.

So JAX-RS is a specification of how a library for implementing REST APIs in Java should look like and RESTEasy is one implementation of that specification.

This effectively means that any documentation on JAX-RS should apply 1:1 to RESTEasy as well.

JAX-RS is a set of interfaces and classes without real implementation that belong to javax.ws.rs.* packages (they are part of Java SE 6, by Oracle).

RESTEasy as well as, for example, Jersey or Apache CXF, are open source implementations of that JAX-RS classes.

During compilation you need only JAX-RS. In runtime you need only one of that implementations.

Query parameters are extracted from the request URI query parameters, and are specified by using the javax.ws.rs.QueryParam annotation in the method parameter arguments.

Example:

@Path("smooth") @GET public Response smooth( @DefaultValue("2") @QueryParam("step") int step, @QueryParam("minm") boolean hasMin, @QueryParam("test") String test ) { ... } URL: http://domain:port/context/XXX/smooth?step=1&minm=true&test=value 

URI path parameters are extracted from the request URI, and the parameter names correspond to the URI path template variable names specified in the @Path class-level annotation. URI parameters are specified using the javax.ws.rs.PathParam annotation in the method parameter arguments

Example:

@Path("/{userName}") public class MyResourceBean { ... @GET public String printUserName(@PathParam("userName") String userId) { ... } } URL: http://domain:port/context/XXX/naveen 

Here, naveen takes as the userName(Path parameter)

Please also note that JAX-RS is only server side specification and RESTEasy has extended it to bring JAX-RS to the client side through the RESTEasy JAX-RS Client Framework.

Info on param, What is the difference between @PathParam and @QueryParam Some great points here regarding params, When to use @QueryParam vs @PathParam - Gareth's answer