I want no monuments

A quick one: AgentSmith has graduated from the javatools incubator and is now part of the javatools project.

Current release (0.8) will become 1.0 during the following weeks.

Ok, I must admit it, I can’t hide: I was wrong. I’ve just discovered that Agent Smith features are already available. To everyone.

A brief explanation.
I’m an Eclipse user. I have been (silly) used in reloading my webapp every time I changed a Struts action or a piece of an Echo2 application.
I wanted to find a way to avoid reloading my webapp.
I saw Groovy. But it didn’t work with Echo2, because of the API.
I saw the Instrumentation interface and I thought: “Hey I will do that: Grovvy won’t be necessary”.
So Agent Smith saw the light. And it was just reaching version 1.0 when I was told that, actually, Eclipse has already a feature like Smith. And it’s really simple to activate it.

So, Smith is dead. Long live to Smith. Thanks to Adrians at the Echo2 forums for finally pointing that out.
I’m very sad, you know. I’ve wasted some days. The most disappointing aspect is that it took two weeks of marketing for someone to come out and say “Hey, you are wrong”.

But!

I know I’m not the only one with this lack of knowledge, so let me flip the bad news in a good news and let me explain how to avoid reloading apps with Eclipse.

Right click on your, say, web project and “Debug as”, “Debug on Server”. Now code.

I can hear you: “Whaaaaaatt? THAT simple!?!?“.

Yes, that simple.

Agent Smith has just been approved by the java-tools community at java.net. It’s currently in the “incubator” but I’m sure it will graduate soon.

This is your new bookmark.

Following my previous post, in the agent smith post series.

Smith comes in two versions: one is java5 only, the other is java6+, meaning you must have at least java 6 (or mustang) to run it.

The two versions differ in one feature only: the ability to load the agent after the jvm start up, instead of the usual way that’s by specifying it with a command line parameter. Anyway, such feature is experimental (even if I use it daily).

Let’s see what to do to begin using Smith.

1. Download the latest version of Smith at the project page and unpack the zip file
2. Run the command:
   

   ant dist

3. Check the dist folder for smith-${version}.jar
4. Download the test classes and unpack the zip file
5. Compile them with
   

   javac Main.java

6. Run them with
   

   java -javaagent:<PATH_TO_SMITH_JAR>=<PATH_TO_CURRENT_FOLDER> Main

   Every path must be absolute.
   You should see two messages repeating every one second

   Bar: I’m doing something
   Bar$Foo: What else???

7. Now open another console and go to the test classes source folder
8. Edit file Bar.java and change the two text printed by System.out.println
9. Compile Bar.java with javac
10. Check the first console: do you see the messages changed?

Easier done than said :)

Next time we’ll set up Tomcat to use Smith into a webapp.

This is the first of a series of articles about Agent Smith. I will begin with an introduction, followed by a “try it, test it how-to”, ending with some examples together with Echo2, Struts and Spring.

As you may know, I am a bit involved with Echo2. Really, I’m a fan of it, I love the way I create ajax UIs coding the swing way. And forgetting the page thing.

But Echo2 has two problems: it consumes a bit of memory (but I don’t really care, since my apps are not intended to be delivered to the world “wild” web) and, if you don’t use EchoStudio, it needs you to reload the webapp to check even small UI changes (obliging you to a constant code-restart-code).

Well, the second problem has been solved. Its solution is called Agent Smith.

Why “agent” ? In java, there are many meanings of the word “agent”. One meaning is a class that has access to the Instrumentation interface, introduced since java 5. With Instrumentation you can call a wonderful method:

void redefineClasses(ClassDefinition[] definitions)

With such method you can change the definition of an entire class, while your program is running. If you have ever played with ClassLoader (creating your own implementations) you know what the method “defineClass” does and you know it is final.
Instrumentation can be used as a workaround to the problem of class redefinition, meaning you can actually use java as a scripting language.

So why not just use Groovy or some other scripting language ?
Because Groovy is slow. Because scripting languages are usually slow. Test Groovy. I found it 18 to 20 times slower that “native” java code.

Java has been criticized by every Microsoft developer for being slow. And they were right. Were. They are no more. Why the heck should I use Groovy to code? Would you shoot at your feet?

But don’t take my humble opinion as a “scripting languages are the wrong way” opinion. Groovy in particular has a lot of nice features (especially the syntax) but, since I’ve read articles about using groovy to speed up Struts actions building, you may find an agent a smarter and cleaner solution.

I think there are times when we really need to avoid app server restart. Think about your JEE application running into JBoss, about your JSF backing bean…
Scripting languages allow us to avoid server (or app) restart, but they also add weight to your code, making it slower.

An agent is a bit hard to set up and so it may not be a good solution. But if you are planning to work on the same project for the following two weeks, then it is.

In the next article I will explain how to compile and set up Smith.

See you soon.