The Grinder

I did some performance testing against a web application that I helped write this weekend. I used The Grinder and was quite happy with the beta version. This lets you write scripts in Jython and uses the quite nice HTTPClient library. The Grinder, like most other performance tools, has an admin interface (the console) and a set up distributed agents that are given tasks and communicate results back via the network to the console. I used the HTTP client, but it looks like you can ‘grind’ anything you can talk to via java, from databases to email servers.

I did run into a few problems. I’m using cygwin on WinXP, and had some difficulties running java from the command line. The fix was to use the cygpath command, like so:

#!/bin/sh
# to start the agent
JAVA=/cygdrive/c/j2sdk1.4.2_03/bin/java
CLASSPATH=`cygpath -p -w /home/Owner/work/grinder/grinder-3.0-beta20/lib/grinder.jar:\
/home/Owner/work/grinder/grinder-3.0-beta20/lib/jakarta-oro-2.0.6.jar:\
/home/Owner/work/grinder/grinder-3.0-beta20/lib/jython.jar`
$JAVA -cp $CLASSPATH net.grinder.Grinder

The client application that I was testing doesn’t use cookies (it’s a J2ME application, and the MIDP spec doesn’t support cookies out of the box). Or rather, it uses cookies, but only to grab the first one that the server sends, store it off, and then pass it back as a query parameter. This type of configuration isn’t The Grinder’s sweet spot, and I had to do a bit of hacking to make sure the appropriate cookie value was sent with the appropriate client request. It would have been nice to use contexts but The Grinder wraps the HTTPConnection in its own class. Apparently, if you are simulating use by a browser, cookies are apparently handled correctly. One gripe–there’s no javadoc for the main classes available on The Grinder’s website, so you have to grab the source if you want to see interactions between pieces (for example, how net.grinder.plugin.http.HTTPRequest interacts with HTTPClient.HTTPConnection).

I also mucked with some of the properties, primarily initialSleepTime. You’ll want to make sure that you read about these properties–I blithely uncommented what was in the sample grinder.properties and ended up with an obscene value for grinder.sleepTimeFactor.

After all the setup, I was able to hammer our server. I discovered two useful things: an error in our logout code, which threw exceptions around 10% of the time, and also discovered that our connection timeout between Apache and Tomcat was set incorrectly. Changing this from 0 to 1000 fixed the dreaded SEVERE: All threads are busy, waiting. Please increase maxThreads or check the servlet status error that I was getting. In addition to these two useful bugs, by making some assumptions about how the application will be used, I was able to gimmick up some interesting numbers about supportable users.

I like The Grinder a fair bit. It’s got a nice GUI. It’s still under active development. I’m a bit leery of using beta software (especially open source beta software), but a poll on the homepage convinced me to try the beta. By using this, I was also able to pick up snatches of python which is a new language to me (finally got to consult my long unused copy of Learning Python). I considered looking at JMeter, but The Grinder appears to be a bit more recently maintained. It’s no LoadRunner, but then again, it doesn’t pretend to be. All in all, if you’re in the market for a cheap, quick performance tool, The Grinder is worth a look.


Miswanting and web application frameworks

I’ve wanted to respond to this post by Kris Thompson where he predicts that “Struts will continue to lose industry acceptance as the MVC leader in the J2EE space” in 2004 for some time now. I believe this is happening already; if you read the blogging community or some of the industry rags, it seems like other alternatives to Struts are being promoted (not least of which is JSF). But there are still tons of Struts applications out there being built every day. There have been over 2000 messages on the struts mailing list for the past year (granted this number is declining–perhaps because folks are GFTFA [googling for the fcuking answer]).

This article explains why I continue to develop in struts: “A wider range of slightly inferior options, then, can make it harder to settle on one you’re happy with.” There is definitely a wide range of J2EE frameworks. In my case, these alternatives to struts are not inferior because of any technical shortfall, but rather because I have to learn them.

(An aside: I have programmers’ optimism as much as anyone else. But after a few years in the industry, I’ve realized that while I feel I can learn a new technology as quickly as need be, in order to really understand the pitfalls of a framework or API, I have to “build one to throw away.” I really do.)

Please don’t take these statements as a whiny “I don’t want to learn anything new.” That’s not true. But my time is finite, and the project deadlines are always creeping up. And struts works well enough for my problem set.

And that’s why struts is going to be around for a while yet.


Long running queries in servlets

The stateless nature of the web presents some user interface issues. Not least of these is how to handle long running processes most efficiently. Do you keep the user waiting, do you poll, etc? Remember, even if everything is going dandy, normal users like to see something.

This JavaRanch article is a good explication of how to use message driven beans and asynchronous access to data in the web tier to deal with these problems. It leans a bit heavily on WebSphere, but does seem to address some of Dion’s issues about there not being enough use of messaging systems. And it even throws a couple of design patterns in as well.


What are EJBs good for?

Dion had a good post about what EJBs are good for. I’ve only used EJBs seldom (and peripherally), but it’s my understanding, from reading the literature, that EJBs are appropriately named–that is, good for enterprise situations. In that case, what on earth are these folks thinking? They demonstrate using an EJB in JSP. What?


SQL Server JDBC driver troubles

I’m responsible for a small struts application for one of my clients. The application was originally coded on Windows against a SQL Server 2000 database. When I was contracted to roll it to production, a Linux box talking to a SQL Server 7 database, I found I couldn’t use the existing MS JDBC drivers, which only support SQL Server 2000. So, I went looking for SQL Server 7 JDBC drivers. There are a ton of choices out there, but most are commercial. I looked at jTDS, but that didn’t work because, at the time, jTDS did not support CallableStatements, which were used extensively by this application. (Apparently, jTDS does now.)

So, I looked at a few commercial drivers, and decided that Opta2000 offered the best feature set for the price ($800 for unlimited web application connections). Then, the database was upgraded from SQL Server 7 to SQL Server 2000. Luckily, we hadn’t bought the JDBC driver yet, so, hey, let’s use MS JDBC drivers–they’re free! Fantastic. The installation went fine (not that it was that complicated–dropping some new jars in the WEB-INF/lib directory and changing some lines in the struts-config.xmlTomcat (version 4.1.24) started behaving badly. With IE (and, to a lesser extent, with Mozilla), the pages started loading very slowly after Tomcat had been running for a while. A restart alleviated this symptom, but didn’t obviously solve the problem. Initially, we thought it was the load, and some misconfiguration of tomcat (tomcat was serving images–not usually considered its strong point, though benchmarks are needed to tell the full tale), but nothing seemed to change the behavior. We tried changing how tomcat was passed requests (mod_jk, mod_proxy), but nothing seemed to work. A colleague of mine looked at when the instability started, and it correlated with the installation of the MS JDBC drivers. So, we switched back to Opta. The application returned to a stable state, and we haven’t seen the problems since. (We plan to purchase the drivers now, although we may take a look at jTDS.)


jad

If you’ve never used jad then you’re missing out on a great tool. Jad lets you easily decompile java class files. It may be shady legally, depending on what contracts you’ve signed, but it’s definitely useful in debugging and understanding behavior of java applications. It couldn’t be simpler to use. Just run

jad classfile.class

from the command line, and you get a java file (named classfile.java) in the same directory. The names of the variables aren’t fantastic (s1, s2…) but it sure beats reading the bytecode output of javap -c.

Note, it’s free for noncommercial use, but if you want to use it commercially, contact the author for terms. And if you get a chance to download it from the above tripod.com link, grab it and store it someplace else, because the page often is unavailable due to its exceeding bandwidth limits.


Book Review: Enterprise J2ME

Update 2/25/07: added Amazon link.

I go to Java Users Groups (yes, I’m struggling to get in touch with my inner geek) once every two or three months. Sometimes there’s an engaging speaker, but most of the time the fellow up front looks like he’s just swallowed a hot pepper, speaks like he has a permanent stutter, and answers questions like I’m speaking Greek. (I’m not making fun; I had a hard time when I was in front of a JUG too.) Regardless of the quality of the speaker, I gain something just by watching the presentation–he points out interesting technologies and usually has a list of resources at the end that I can use for further research.

I think Michael Yuan would be a great speaker at a JUG, as he seems to have a masterful understanding of Java 2 Platform, Micro Edition (J2ME). However, the true value of his book, Enterprise J2ME, was in its introduction of new ideas and concepts, and the extensive resource listings. This book is a survey of the current state of the art in mobile java technology. Whatever your topic is, except for gaming development, you’ll find some coverage here. Securing information on the device or network, XML parsing strategies, messaging architectures, and data synchronization issues are all some of the topics that Yuan covers.

My favorite chapter was Chapter 7, ‘End to End Best Practices.’ Here, Yuan covers some of the things he’s learned in developing his own enterprise applications, and offers some solutions to five issues that differ between the J2ME world and the worlds familiar to most Java developers: J2EE and J2SE. He offers capsule solutions to the issues of “limited device hardware, slow unreliable networks, pervasive devices, ubiquitous integration [and] the impatient user.” Later in the book, he explores various architectures to expand on some of these capsules.

However, the strength of this book, exposing the reader to a number of different mobile technologies, is also its weakness. JUG speakers very rarely dive into a technology to the point that I feel comfortable using it without additional research; I usually have to go home, download whatever package was presented, and play with it a bit to get a real feel for its usefulness. This book was much the same. Some of the chapters, like chapters 12 and 13, where issues with databases on mobile devices (CDC devices, not CLDC devices) weren’t applicable to my kind of development, but you can hardly fault Yuan for that. Some of the later chapters felt like a series of ‘hello world’ applications for various vendors. This is especially true of chapter 12, and also of chapter 20, which is a collection of recipes for encryption on the device.

Additionally, I feel like some of the points he raised in Chapter 7 are never fully dealt with. An example of this is section 7.3.3, “Optimize for many devices.” The project I’m on is struggling with this right now, but I had trouble finding any further advice on this important topic beyond this one paragraph section. However, these small issues don’t take away from the overall usefulness of the book–if you are developing enterprise software, you’ll learn enough from this book to make its purchase worthwhile.

However, I wouldn’t buy the book if you’re trying to learn J2ME. Yuan gives a small tutorial on basic J2ME development in Appendix A, but you really need an entire book to learn the various packages, processes and UI concerns of J2ME, whether or not you have previously programmed in Java. Additionally, if you’re trying to program a standalone game, this book isn’t going to have a lot to offer you, since Yuan doesn’t spend a lot of time focused on UI concerns and phone compatibility issues. Some of the best practices about limited hardware may be worth reading, and if it’s a networked game, however, you may gain from his discussions in Chapter 6, “Advanced HTTP Techniques.” In general though, I’m not sure there’s enough to make it worth a game developer’s while.

I bought this book because I’m working on a networked J2ME application, and it stands alone in its discussion of the complex architectural issues that such applications face. It covers more than that, and isn’t perfect, but it is well worth the money, should you be facing the kind of problems I am. Indeed, I wish I had had this book months ago, as I’m sure it would have improved the my current application.

Link to book on Amazon.


Jalopy

I like javadoc. Heck, I like documentation. But I hate adding javadoc to my code. It’s tedious, and I can never remember all the tags. I don’t use an IDE so the formatting gets to me.

After attending a presentation at BJUG about software tools, I investigated jalopy and I liked what I found. Now, jalopy is more than just a javadoc comment inserter, but javadoc insertion was my primary use of the tool. It may be piss poor for code formatting and whatnot, but it was pretty good at inserting javadoc. I was using the ant plug-in and the instructions were simple and straight forward. It didn’t blow away any existing comments, and it didn’t munge any files, once I configured it correctly. And there are, make no mistake, lots of configuration options.

Jalopy has a slick Swing interface to set all these configuration options, and you can export your configuration to an XML file which can be referenced by others. This, along with the ant integration, make it a good choice for making sure that all code checked in by a team has similar code formatting.

However, I do have a few minor quibbles with this tool.

1. The default configuration of javadoc is busted. When you run it, it javadocs methods and classes just fine, but any fields are marked with “DOCUMENT ME!” when they should be commented out: “/** DOCUMENT ME! */”. This means that, with the default configuration, you can’t even run the formatter twice, since jalopy itself chokes on the uncommented “DOCUMENT ME!”.

2. The configuration file is not documented anywhere that I could find. I looked long and hard on the Internet, and only found one example of a jalopy configuration file here. And this is apparently just the default options exported to a file. I’ve put up a sample configuration file here which fixes problem #1. (This configuration is only for javadoc; it accepts all other defaults.)

3. The zip file that you download isn’t in its own directory. This means that when you unassumingly unzip it, it spews all over your current directory.

None of these are show stoppers, that’s for sure. If you’re looking for a free, open source java code formatting tool, jalopy is worth a close look.


Java Tidbits

Quick, take this true/false quiz and test your Java(tm) knowledge:

1. Private members can only be accessed by the object which owns them.

2. The contents of a finally block are guaranteed to run.

Everybody knows that both of these are true, right?

Actually each of these is false. In the first case, this program shows that objects can twiddle with private members of other objects of the same class:

class PrivateMember {
   private int i; 
   public PrivateMember() { 
      i = 2;
   }
   public void printI() {
      System.out.println("i is: "+i);
   }
   public void messWithI(PrivateMember t) {
      t.i *= 2;
   }
   public static void main (String args[]) {
      PrivateMember sub = new PrivateMember();
      PrivateMember obj = new PrivateMember();
      obj.printI();
      sub.messWithI(obj);
      obj.printI();
   }
}

and this program shows that finally blocks don’t run if the JVM exits:

class TryCatch {
   public static void main (String args[]) {
      try {
         System.out.println("in try");
         throw new Exception();
      } catch (Exception e) {
         System.out.println("in catch");
         System.exit(0);
      } finally {
         System.out.println("in finally");
      }
   }
}

J2ME development advice

Here is some advice for any of you thinking about doing any development for J2ME. I’ve written before on J2ME considerations, but the project I’m working on is a bit further on now, and I thought I’d share some hard earned knowledge.

1. Get Windows.

Make sure you have access to a windows box, running a modern version of windows. While Sun’s Wireless Tool Kit supports Linux and Solaris, and IBM’s WebSphere Device Developer supports Linux, no other emulators do (nor do they work under wine).

Whether you want to support Motorola, Nokia, or NEC, you are pretty much need windows to run the emulator. And an emulator is crucial, because it allows you to rapidly develop an application. And testing on as many emulators as possible means that your application will be as tight as possible. However, when you get something that is close to finished, you’ll need a real phone to test it on.

2. Get (a) real phone(s).

While emulators can tell you a lot, they certainly can’t assure you that an application will run on a real phone. One project I worked on had an emulator that ran the app just fine, but the app was locking up on the real phone. It turned out that the networking code needed to run in a separate thread. There are many things that differ between an emulator and a real phone. Installation of a midlet is different (and differs between phones as well). Instead of accessing a file on disk, you have to use OTA provisioning (sure you can emulate that with the WTK, but that’s just an emulation. I’ve run into issues with DNS that just don’t show up on the emulator). Also, as mentioned above, the networking capability differs, and the connection is much slower. The amount of memory that you can use while developing on the desktop is effectively unlimited (some of the emulators let you monitor the amount used, but I don’t know of any that lets you limit it), but phones have hard limits. Don’t you want to know what happens when you try to use 101KB of memory on a device that only has 100KB? The limitations you face on user interface are also more real on a phone, when you can’t use the keyboard to enter your username or the backspace key to fix errors. For all these reasons, you should get a phone as soon as you can.

3. Explore existing resources.

A couple of good books: Enterprise J2ME is a great survey book, with some very good ideas for building business applications (with large numbers of users) but not a whole lot of nuts and bolts. Wireless Java: Developing with J2ME, Second Edition is a good nuts and bolts book (it explains how to do your own Canvas manipulations, for example). Check out what else Amazon suggests for other ideas.

A couple of helpful urls: Fred Grott’s weblog, MicroJava, the EnterpriseJ2ME site, Sun’s site, of course, and the javaranch saloon is pretty helpful too.

The various carrier websites are useful, if only to find out what kind of phones you want to target: AT&T, Sprint, T-Mobile, Nextel. (Verizon in the USA is BREW only.)

4. Have fun.



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