Jersey

From APIDesign

Jersey, a reference implementation of JAX-RS (JSR 311), intended for building RESTful Web services. I was impressed by the framework and decided to build my project on it in 2009. Now it is 2012 and time has come to ask whether it was a good choice. Is Jersey a good technology?

REST is Cool!

There are three parts that make a technology good. Coolness being one of them. REST has been cool for few years. JAX-RS is cool as its Java realization. Jersey is the reference implementation of JAX-RS. All of this makes it very easy to choose Jersey as your technology (not counting the fact that most of the team that develops it sits one from above my office).

No web.xml

The other part of good technology is time to market. Jersey delivers acceptable results in this respect as well. As being long time Java SE guys, I especially like the fact that Jersey can run outside of any web container like Tomcat or Glassfish. I am afraid of web.xml and disgusted when I have to touch it. With Jersey I could get my server up and running without paying attentiong only to what was important to me - the methods annotated with @GET and @POST.

Jersey also comes with a special testing framework which makes the process of testing REST application relatively easy. This is good for time to market as well, as these days people want to ensure the amoeba shape of they application with bunch of tests before they release.

Time to market is good with Jersey.

No Server Side Push

In 2009 I could confirm that I like the Jersey framework a lot. There was just one thing I was missing. As I am using Jersey to implement a board like game server, I'd like to notify the clients about changes made to the board as soon as they happen. I needed server side push like Comet computation model.

For two years I've been chatting with the Jersey guys and got promise they will implement it. I was patient, in spite of having a feeling there are other implementations of JAX-RS out there, that already support server side push.

However, you know how it, people are lazy and rewriting to a different implementation seemed like too much work. In spite the base API is the same (e.g. JAX-RS) the devil lays in details. All the configuration and additional APIs around just convinced me to wait.

Upgrade to 2.0

I was patient and my time has come. Jersey 2.0m3 was announced with support for @Suspend and it was the time to make the switch! But that has been the beginning of the nightmare! Since then it is hard to say anything good about Jersey. As the library user I feel disappointed and betrayed.

The Code

One would expect that upgrading a dependency on Jersey is as easy as going to pom.xml of my project and replacing 1.6 with 2.0m3. You would be surprised, it is not like that at all. It is much more painful.

First of all, there no version 2.0m3 offered in the list of available versions. OK, I thought, maybe it is because it is not yet stable version. But then I realized that the version is available, but with completely different group and artifact identifiers. Instead of com.sun.jersey one needs to use org.glassfish.jersey.core or org.glassfish.jersey.containers or org.glassfish.jersey.media.

Looks like the Jersey team will now more closely work with rest of Glassfish. Good for them. Bad for poor users like me! Renaming widely used library just because you are now part of another organization is not user friendly. Compare with Hudson or JNA which both keep their original packages in spite being part of Eclipse foundation or in the case of JNA keeping com.sun prefix, in spite no longer being maintained by anyone with relation to Sun/Oracle.

However my Jersey struggle was not over. Not only I needed to change the library names. Not only I had to rename imports of packages all over the code base (like com.sun.jersey.api.json.JSONWithPadding to org.glassfish.jersey.media.json.JsonWithPadding), but I had to really change the code! Concepts are different. For example instead of

ResourceConfig rc = new PackagesResourceConfig("cz.xelfi.quoridor.webidor");
HttpServer server = GrizzlyServerFactory.createHttpServer(baseUri, rc);

I had to invent following code:

ResourceConfig rc = ResourceConfig.builder().
    packages("cz.xelfi.quoridor.webidor").build();
HttpServer server;
server = GrizzlyHttpServerFactory.createHttpServer(
    baseURI,
    Application.builder(rc).build()
);

I am not sure if this the right replacement (see below), but it is the simplest code I could find that promises to do the same as the original one. But the primary question remains: Why I need to change my code at all!?

Some people believe that when doing Big Bang rewrite, it is better to do it as big as possible. Cleaning up names of classes and changing calling flow for sake of something. I don't find such approach [[good]. It hurts total cost of ownership and clearly shows that the library authors don't care about users of previous version of their library.

The Test Framework

However bad the treatment described above is, there is something even worse: upgrading the tests is even more difficult. After a bit of searching I found the group and artifact id where JerseyTest lives, but then I realized that it has been changed significantly!

Methods are returning different parameters (like configure()) and it is not easy to find a replacement. Some methods don't even exists (for example resource). As a result my tests are full of errors and I don't have a slightest idea how to fix them.

C'mon Jersey developers, in many projects tests are the glue that holds the whole project together. They contain the knowledge what the project should do. I no longer have it, as during last two years I was doing something else (yes, I am clueless), but that is the primary reason I write tests: to let them remember instead of me!

If you say that I have to rewrite all my tests before I can switch to Jersey 2.0, it is like suggesting me to start from scratch!

Big Bang

Looks like some people really believe that Big Bang is natural part of software developement. Well, I don't. I want the Jersey team to write a compatibility bridge to guarantee I can just change the Jersey version and everything will continue to work. I am afraid I am not going to get any support like that. In such case, farewell, as I bet on bad horse. Projects that don't preserve investments of their users should be damned.