How to set up JAX-RS Application using annotations only (no web.xml)?

Question

Is it possible to set up a JAX-RS application using annotations only? (using Servlet 3.0 and JAX-RS Jersey 1.1.0)

I tried and had no luck. Using some web.xml seems required.

---

Configuration A (working, but has web.xml configuration)

web.xml

   ...
   <servlet>
      <servlet-name>org.foo.rest.MyApplication</servlet-name>
   </servlet>
   <servlet-mapping>
       <servlet-name>org.foo.rest.MyApplication</servlet-name>
       <url-pattern>/*</url-pattern>
   </servlet-mapping>
   ...

Java

@ApplicationPath("/")
public class MyApplication extends Application {
    ...
}

---

Configuration B (not working, exception thrown)

@ApplicationPath("/")
@WebServlet("/*") // <-- 
public class MyApplication extends Application {
    ...
}

The latter seems to insist that the Application will be a subclass of Servlet (the exception leaves no guesswork)

java.lang.ClassCastException: org.foo.rest.MyApplication cannot be cast to javax.servlet.Servlet

---

Questions

1. Why the web.xml definition worked but the annotation didn't? What's the difference?

2. Is there a way to have it worked, e.g. have a JAX-RS Application with no web.xml?

Answer 1

** PLEASE READ IF YOU USE TOMCAT OR JETTY! **

The accepted answer does work, but only if the webapp is deployed to an app server like Glassfish or Wildfly, and possibly servlet containers with EE extensions like TomEE. It doesn't work on standard servlet containers like Tomcat, which I'm sure most people looking for a solution here want to use.

If you're using a standard Tomcat install (or some other servlet container), you need to include a REST implementation since Tomcat doesn't come with one. If you're using Maven, add this to the dependencies section:

<dependencies>
  <dependency>
    <groupId>org.glassfish.jersey.bundles</groupId>
    <artifactId>jaxrs-ri</artifactId>
    <version>2.13</version>
  </dependency>
  ...
</dependencies>

Then just add an application config class to your project. If you don't have any special configuration needs aside from setting the context path for the rest services, the class can be empty. Once this class is added, you don't need to configure anything in web.xml (or have one at all):

package com.domain.mypackage;
import javax.ws.rs.ApplicationPath;
import javax.ws.rs.core.Application;

@ApplicationPath("rest") // set the path to REST web services
public class ApplicationConfig extends Application {}

After this, declaring your web services is straight forward using the standard JAX-RS annotations in your Java classes:

package com.domain.mypackage;
import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.GET;
import javax.ws.rs.MatrixParam;
import javax.ws.rs.Path;

// It's good practice to include a version number in the path so you can have
// multiple versions deployed at once. That way consumers don't need to upgrade
// right away if things are working for them.
@Path("calc/1.0")
public class CalculatorV1_0 {
  @GET
  @Consumes("text/plain")
  @Produces("text/plain")
  @Path("addTwoNumbers")
  public String add(@MatrixParam("firstNumber") int n1, @MatrixParam("secondNumber") int n2) {
    return String.valueOf(n1 + n2);
  }
}

This should be all you need. If your Tomcat install is running locally on port 8080 and you deploy your WAR file to the context myContext, going to...

http://localhost:8080/myContext/rest/calc/1.0/addTwoNumbers;firstNumber=2;secondNumber=3

...should produce the expected result (5).