A great article by Stefan Tilkov on Addressing doubts on REST. This and his previous article are a must read for any REST noob. I wish I had them available when I was researching REST almost a year ago.
Reliable concurrent initialization
March 13, 2008
I recently ran into the situation where I wanted to do lazy, on-demand, initialization of a registry. In previous applications, I would just use get()/put() from java.util.ConcurrentHashMap because I didn’t care if something was created more than once accidentally as it would eventually, and quickly, sort itself out and all I’d lose is a tiny garbage collection. Unfortunately, in my current project, a registry entry cannot be allocated twice as two different versions of it might be used concurrently and each registry entry holds and maintains state. These resources need to be individually unique. Thankfully, java.util.ConcurrentHashMap has a nice method called putIfAbsent(). This method does the atomic equivalent of:
if (!map.containsKey(key)) {
return map.put(key, value);
} else {
return map.get(key);
}
So, what I can do is do a mini double check. When I lookup at entry, if it doesn’t exist, allocate a temporty version of it and call putIfAbsent.
public V get(K key) {
V value = concurrentMap.get(key);
if (value != null) return value;
value = new Value(...);
V tmp = concurrentMap.putIfAbsent(value);
if (tmp == null) {
return value;
} else {
value.cleanup();
return tmp;
}
}
If putIfAbsent returns null, then I know nobody has created a version concurrently. If it doesn’t return null, then I know somebody has initialized this entry concurrently. In that case, I cleanup the created value, and return the one already in the registry. This looks a lot like the double-check-nono, but it actually isn’t as ConcurrentHashMap performs the putIfAbsent atomically.
RESTFul XML content negotiation
March 5, 2008
I’ve been playing around a little bit with the idea of creating a RESTFul MOM/ESB where the client requests a specific format and the server transforms the content if it can. For an ESB, this usecase would normally turn up for various XML-based messages and documents. The client would request an XML document of a certain schema and the ESB would return that format, performing a transformation if applicable.
For a RESTFul ESB, I’d want to use HTTP content negotiation. The problem is, AFAIK, there is no standard MIME type, other than “application/xml”, that allows you to specify an XML format with schema information. Being a REST noob, I emailed my friend Steve, a REST enthusiast, and asked him if it would be ok to embed schema information into the media type. My first thought was the media type would be:
application/myschema+xml
Steve’s response was you can’t just make up a MIME type on your own and expect it to work well on the Internet without registering it. At first I thought, what’s the big freakin deal? But then I realized, what if you want to point your browser to a message in a remote RESTFul queue and just view its content? If you use “application/myschema+xml” your browser ain’t gonna understand it.
So, I decided to do a search on “decentralized mime types” and came across a few blogs from Stefan Tilkov, Dan Diephouse, and James Strachan. Here’s a summary (sorry if I left out anything)
Use AtomPub
One idea was to use AtomPub . I don’t like this idea at all. One, I just want to send a bloody XML document! KISS baby KISS! Second, if I’m going to use an envelope format, why not just use SOAP and WS-*? (no thanks). This, IMO, sort of defeats one of the general principles of REST.
Define a new decentralized MIME type
The idea would be to define a decentralized MIME type like this:
application/data-format;uri=http://mediatypes.example.com/foo/bar
The uri would point to something like an RDDL document that defined the real format. Beyond KISS, what I don’t like about this approach is that again, I have no way of pointing my browser (or some other generic client) at the resource and just viewing it.
Use MIME properties
I saved the best for last. The final idea was to embed format information within MIME properties:
application/xml; schema="http:/..." application/octet-stream; data-format=java
Use a registered MIME type, but append extra format information as a MIME property. I did a test on this with Firefox and Safari and it doesn’t screw up the viewing. So for me, MIME properties it is! I would be interested in links to other thoughts on this.
Resteasy Project: JAX-RS Restful Web Services implementation
February 25, 2008
java, jboss, REST, Webservices 12 Comments
I’m pleased to announce the first beta release of the JBoss Resteasy JAX-RS implementation!
After about 4 months of on and off development, I finally have a working version of the new JSR-311, JAX-RS specification. For those of you who don’t know, JSR-311 is a RESTFul Web Services implementation for Java and is slated to be included within Java EE 6. The spec is still a bit of a moving target, but its still pretty useful. Let me know what you think!
Features:
- JAX-RS implementation (almost full, still have a few minor things here and there)
- Portable to any app-server/Tomcat that runs on JDK 5 or higher
- EJB 3.0 and Spring integration
- Client framework to make writing HTTP clients easy (JAX-RS only define server bindings)
Where can I find out more?
All information, including where to download it, is available on our Resteasy WIKI.
Scannotation fix for /WEB-INF/classes
February 14, 2008
I have a confession. I didn’t really test the code that allowed you to scan /WEB-INF/classes for my Scannotation project. In the old code, if you run within Tomcat, you’ll get a “jndi:” protocol based URL that my code doesn’t understand yet how to scan
Instead, I obtain the URL by doing a ServletContext.getRealPath(“/WEB-INF/classes”). Unfortunately, this is not guaranteed to work by the specification, so, if you run into this problem, you’re gonna have to find another way to scan this directory portably.
I’ve released a version 1.02 of Scannotation that has this RealPath fix along with a few other minor bug fixes I found while using the library.
EJB maintains its dominance
February 13, 2008
ejb3, seam, spring 22 Comments
EJB was created almost 10 years ago to solve the component needs of application developers. Since then thousands of successful applications have been written and deployed using this technology. Although I don’t do much with EJB nowadays as I have other responsibilities at JBoss, I still wonder how it is doing in the industry. Recently, I became privy to various bits of knowledge that EJB is still going strong and maintaining its dominance in Java application development. Consider this job trends graph from indeed.com:
Over 3 years EJB jobs have remained pretty much constant. This is very encouraging news considering recent Rod Johnson propaganda. EJB really did not have an alternative in the Java space until 2004/2005 when Spring started to be known and popular. It is very interesting to see that although EJB has had a serious competitor, it has maintained its dominance in Java application development over the years. You could even extrapolate from these numbers that EJB is an upper bound on the number of Java component jobs out there and that Spring has only recently matched this. This is proven by the fact that the Spring and Java graph trends are the same since they converged 6 months ago.
This trend pretty much correlates with download numbers I posted on our EJB implementation awhile back on TSS in June 2007.
I can give you a few from two perspectives:
downloads on sf.net for JBoss and Hibernate projects related to EJB3 and JPA:
* Downloads of a standalone distribution of the JBoss EJB3 project since 10/2004: 183199
* JEMS installer which bundles EJB 3.0 (not same as JBoss Appserver download): 201923
* JBoss 4.2 which bundles EJB 3.0: ~65000
* JBoss 5 betas which bundles EJB 3.0: ~80000
* Hibernate’s JPA implementation: 135269
* Hibernate Annotations (which is JPA based): 202561
So, total downloads solely related to JPA: ~337K
Total downloads solely related to EJB3: ~550K
Total EJB3 + JPA related downlaods: ~ 887KCompare that to Spring 2.x downloads: ~600K
Spring 1.x downloads: 946K
Hibernate 3.x downloads: 1445K
Hibernate 2.x downloads: 495KNow that’s just JBoss. You also have Glassfish, Open JPA, Oracle, and now Geronimo communities not included in these numbers.
Also, my EJB 3.0 book has been out a year and has sold ~12K copies +/- a thousand (haven’t gotten check yet from last quarter).
So, all and all I think there is pretty compelling evidence that EJB3 and JPA has momentum.
Its hard to continue any analysis on JBoss specific download numbers as we basically encourage our user base to download JBoss 4.2.x or 5 as it is bundled with our EJB3 implementation.
There’s some other encouraging numbers as well. In 2005 I was offered by O’Reilly to take over Richard Monson-Haefel’s EJB series. “EJB 3.0, 5th Edition” was published in May, 2006. Even after being out for almost a year and half, sales are still going strong. Just last quarter we sold 1700 copies, very good for a technical book. When I went to Krakow in October, I also found that my book had been translated into Polish. I believe its also been published in Chinese. All indicators of broad adoption by the technology.
So, as you can see, even after almost 10 years, EJB is still going strong and maintaining its dominance. With the emergence of Seam and Web Beans being incorporated into EE 6, I predict this trend to continue.
Yahoo/Zimbra acquisition opportunity for Buni?
February 7, 2008
Recently, I was browsing around reading about the possible Yahoo! acquisition by Microsoft. One Washington Post article in particular talked about how Zimbra customers are spooked by the acquisition. Zimbra is a commercialized open source mail server distribution that competes with Microsoft Exchange. This got me thinking, Andy Oliver must be really happy right about now as it creates a nice opening and opportunity for his company Buni. Buni was originally the JBoss Mail project. I remember Andy 2 years ago presenting his project and business opportunity to JBoss’s technical board of directors. Back then, it was pretty impressive what he and his project contributors had accomplished. Since then, Andy left Red Hat shortly after the acquisition to pursue his entrepreneurial ambitions for his mail project after we failed to give him the support he needed to make it succeed at JBoss. I can only imagine how much better his distribution has become since he was able to work on it full time. I know they have some solid reference customers and a thriving community.
Anti-IDE Myths
February 6, 2008
flame bait, java, ruby 10 Comments
Well, if you were wondering who my evangelist colleague was in my “Dynamic Languages: Rationalizations and Myths” blog, wonder no more. Please go read Steve Vinoski’s comments, they are a good read. One of my major points against dynamic languages was the inability for an IDE to provide reliable refactoring for them. Steve attacked this with a considerable amount of drivel. Here’s some good blurbs:
“The contrived Ruby example that Bill uses to “prove” [that dynamic languages can’t do reliable refactoring] is, well, contrived. Why would anyone write code like that or suddenly get the urge to rename init to init2? I’m no Ruby expert, but I’d probably rename the method and then stick a method_missing in there to catch any call instances I might have missed with my editor. “
Contrived my ass…Like I said in my previous blog. I write sucky code. I am constantly renaming methods, extracting methods, combining methods, renaming classes, deleting unneeded methods, fields, classes all the time. I never get things right the 1st time and rarely get them right the nth time. Steve, 99% of us are not the uber programmer you are. And, what Steve? Am I going to have to do a constant edit/test/edit/test continuously until I get my edits right? Sounds a lot less productive than having the IDE automatically and reliably do it for you with one click. Again Steve, I used to be in your world. Not as long as you, but still a considerable amount of time.
“I asked him if these magical modern IDEs that raise productivity and eliminate common errors also eliminate defects caused by missing or misunderstood requirements, missed use cases, or just plain ol’ bad programming. Again, no answer. The reason I asked this is that those are the bad bugs; syntactical errors are really the least of your worries. Even if the IDE spits out common idiom/pattern skeletons for you, it’s still quite possible to screw up the code logic, and neither the IDE nor the compiler is going to prevent that.”
Nice strawman Steve. When did I ever say or infer this? How is implementing in a dynamic language going to “eliminate defects caused by missing or misunderstood requirements”? It sure is going to be a hell of a lot easier to refactor your codebase to fix these problems, but eliminate? So Steve, are what you really saying is “IDE’s are not going to eliminate your bugs or poor design”? Thanks for stating the obvious. What I keep telling you is that I’m going to be 10 times more productive with a statically typed IDE when I try to fix these poor designs and logic.
“Considering how old Java is, it’s obvious that it’s taken quite a bit of time to get these IDEs to where they are today. I asked Bill if everyone should have to wait a long time, on the order of 10-15 years, before an IDE truly becomes valuable for a given language. No answer. Personally, I’d rather stick to my emacs and UNIX tools, with their infinite applicability and flexibility that can be used for development in pretty much any language, than wait around for someone else to give me a far less functional IDE that barely addresses only one language. But then again, if one language is all you got, then I guess you have no choice.”
Reality: One, I don’t remember him asking me this. Two, I think that IDEs (at least Intellij) are so well designed now that they can easily support a variety of languages fairly quickly. Add to this fact that their APIs are open (not OSS, but open) and have a great community. For instance, on a quick search I found plugins for Ruby, Python, AspectJ, XML, XML Schema, and Scala. The interesting thing about Intellij, is that it also has support for frameworks. For example, it has syntax checking and code completion for embedded Hibernate/JPA QL. Refactoring integration between Spring, JavaEE and Java. I haven’t looked at their RoR support, but I bet it is awesome. I continually find it AMAZING how these guys bang things out. They are either an army of people (doubtful) or just have an incredibly architected product (probable).
“I asked Bill if he’s ever considered that Java IDEs are the way they are due to issues with the Java language itself that must be compensated for. Consider its verbosity, for example, which is why IDEs spit out those skeletons.”
Reality: Let me go through the list of Code Gen and Refactoring items and see what is not useful in, let’s say, Ruby. There are 30 refactorings in IntelliJ + Java. Only 8 out of 30 are NOT useful to Ruby. For the “Generate..” code generation tab. 2 out of 5 are not useful for Ruby. I think the “Surround With..” tab is useful. The thing is, out of these 35 things, I *DO* use one of them *at least* every 10 minutes. This is of course assuming you believe that the unuseful things are because Ruby is a better language (I don’t beyond the closure stuff). I will admit that only 5 of the refactorings require a statically typed language to be *reliable*, but, at least for me, I do use these particular ones very very often, especially after the first prototype. (rename, move, safe delete, change method signature, inline). At least with Intellij, parameter types are also extremely useful with code completion. Good code is self documenting and with IDE code completion, I don’t have to look at a manual or source code comments to find out how to execute a method on an object. BTW Steve, what “skeletons” are you talking about? MDA bullshit? Or the crap I rarely use?
“Saying that “my buddy Jason was on a team that had to put type names in their Python function names” is certainly not even close to being solid evidence of your claim, Bill.”
Steve, I think Jason’s experience was a relevant experience. I wrote about it because I thought Jason’s experience was the funniest story I’ve heard. It sure isn’t the only horror story people have had with lack of static typing.
I feel responsible for Pats loss
February 5, 2008
I just found out some information that for some reason makes me feel responsible for the Patriots loss. Know who Plaxico (Giant’s wide receiver who caught game winning touchdown) Burress’s QB was in college? BILL BURKE! Yes, this is not a misprint Bill BLEEPIN Burke!!! Check out this article I found on a game Bill Burke and Plaxico played together in college.
Well, it seems Mr. Burke beat Michigan to remain undefeated at the time. Guess who was the Michigan QB? YUP, FREAKIN TOM BRADY!!!! I almost shit my pants.
Know how I found out about this? Well, I was looking at my blog stats and found that somebody had found my site by searching “Bill Burke vs. Tom Brady”. I was like WTF would somebody do a search like that? Lo and behold….
Other dynamic language propaganda
February 4, 2008
flame bait, java, ruby 4 Comments
One of the commenters of my last blog reminded me of yet another myth:
If you learned to code in the XXX dynamic language way you’d need to rely a lot less on your IDE.
And Joe Johnson wasn’t the first to say that to me. 🙂 Another tactic I can’t stand with the zealots in the dynamic language community (and any other religious communities I might add.) Attack your criticizer’s insecurities. This comment translates to, “Java has made you a sucky programmer, if you program in Ruby, you will no longer be a sucky programmer” Or, simply: “Ruby will make you an UBER programmer” or, even simpler “You are a sinner, you must be saved”. This is an awesome way to promote your language. Why? Well, because most of us programmers are geeks. We were laughed at in school for wanting to spend our free time copying game code from magazines. Even beat up. So, we are inherently insecure and eager to be accepted by any crowd.
The problem with this argument is, for me personally, what happens when I switch to Ruby and miss the productivity I had with my Java IDE? Does this mean I’m a horrible programmer and still a loser? You readers know how insecure I am. So, I just can’t switch to Ruby. When I fail at becoming the uber programmer I always wanted to be after switching to Ruby, my insecurities and closet-Rod-Johnson-loving, fragile ego will just shatter me and I will end up crying myself to sleep every night. Sorry no thanks. I already had enough heartache watching the biggest choke in NFL history yesterday. I can’t take anymore. The reality is that I know I am a horrible programmer and switching to Ruby won’t change that fact. At least if I stay with Java, others will have the tools to productively clean up the messes I leave behind.
Many are still scared by the dot.com bubble burst. Many were laid off at least once. So, its only natural to prey on these types of insecurities as well. The reality is, if you read the fine print, Ruby is still only a tiny percentage of the Java market. Even if it continues at this growth rate it will be at least 3 years before it overtakes Java. Which is fine for me as, about that time, I have to start looking for another job as, obviously, SpringSource will have put JBoss out of business by then. I’m fine with that. 3 years is enough time for me to collect the rest of my stock and get my wife back to work to take care of my ultimately unemployed ass.
The non-programmers of the world need a simple language to code in
Beautiful! You mean my 94 year old grandma can help me code? The problem with this is that this leaves a huge mess to clean up after the fact. That’s great for the $100-200/hour consultant out there cuz they can bill thousands of hours. Sucks for the company paying the bills.
Bill the Plumber 