Charles Hope and the Luminous Top

System Equivalents and Computers

There's an equivalence between quantities in mechanics and electrical circuits. Given the similarity between F = −kx = C dx/dt = M d²x/dt² and V = Q/C = R dQ/dt = L d²Q/dt², we can say that Force : Voltage, Springiness : Capacitance, Mass: Inductance, and Damping: Resistance.

Is there any equivalent to the quantities we care about when designing software, such as CPU operations, memory, network bandwidth, and disk speed?

I hate you too, jar manifest! (The sequel)

If a the last line of a jar manifest is a class path and it doesn't end with a new-line, Java will croak, complaining that the jar is corrupted. Let's see you figure that one out!

Finally, a build system for Java programmers

Justin Lee has created the Gosling project on java.net. Gosling is a build processor similar to Ant except that instead of using XML for execution, it uses a Java source file. The code looks like this:

    @Description("Builds the distribution bundles")
    public void dist() {
        clean();
        jar();
        mkdir(DIST_DIR);

        new Copy(this)
            .setDestDir(new File(DIST_DIR + "/bin"))
            .addFileSet(new FileSet(BIN_SRC_DIR))
            .execute();

        new Copy(this)
            .setDestDir(new File(DIST_DIR + "/lib"))
            .addFileSet(new FileSet(BUILD_DIR)
                .addInclude("*.jar"))
            .execute();

        new Zip(this, new File(DIST_FILE))
            .addFileSet(new FileSet(".")
                .addInclude("build.*")
                .addInclude("src/**")
                .addInclude("lib/*.jar"))
            .execute();
    }

Great work, Justin! I've been waiting years for this.  I've been using ant for five years now and I still haven't memorized the differences between file list and file set. Which one goes inside a path element?  I just mess with it until it works, or copy fragments from other projects. Does anybody really have to explain why Java is a superior programming language than XML!? But of course, they do to some folks at The Server Side, who utter such profundity as

If you thought XML build scripts were hard to read and understand, how is this better?

Getting started with Chainsaw, the log4j analyzer

This documentation was written because there doesn't seem to be a five-minute introduction anywhere on their site.  I had to hit multiple web sites to compile this basic information.

Your log4j.xml must contain an appender that goes to a file and uses the XMLLayout. Here's a sample:

    <appender name="chainsaw_log" class="org.apache.log4j.RollingFileAppender">
        <param name="File" value="blipfoot.log.xml"/>
        <param name="Append" value="true"/>
        <param name="Threshold" value="DEBUG"/>
        <param name="MaxFileSize" value="100MB"/>
        <param name="MaxBackupIndex" value="2"/>
        <layout class="org.apache.log4j.xml.XMLLayout" />
    </appender>

You can use Chainsaw 1.2, which ships inside the log4j distribution. Run it like this:
java -classpath log4j-1.2.12.jar org.apache.log4j.chainsaw.Main
Or you can use Chainsaw 2, which is at this Java Web Start link.

Version 2 gives you pretty colors, I haven't yet figured out how to filter by logging level, which is pretty important.  Version 1.2 couldn't make it any clearer: there's a level drop down placed prominently.

I hate you too, jar manifest!

Jar manifests, the bane of all Java developers.  Why weren't regular properties files sufficient?

My jar required two additional linked library jars in its class path, so I added them into the ant build script which I use to create the jar.  Suddenly my application stopped working.  After some confusion, I opened up the jar manifest file and saw that the class path line was cut off in the middle of one of the jar names! I tried several ways to break the line between jar names, but none of them worked.

Ant's FAQ is positively rude on the issue.  It reads

Ant implements the Java Jar file specification. Please refer to the notes section where it discusses the maximum allowable length of a line and the concept of continuation characters.

That is completely unhelpful, because the Jar file specification says

No line may be longer than 72 bytes (not characters), in its UTF8-encoded form. If a value would make the initial line longer than this, it should be continued on extra lines (each starting with a single SPACE).

and the ant FAQ doesn't explain how to create such a continued line in a manifest file!

Then check this out: Bug ID: 4482804 Class-Path mangled in Manifest. It says:

If you do not want to have long lines , you could also do it like this

Manifest-Version: 1.0
Main-Class: Main
Created-By: 1.3.1 (Sun Microsystems Inc.)
Class-Path: /lib/utils.jar /lib/xmlutil.jar /lib/db.jar
Class-Path: /lib/log4j.jar /lib/referencedata.jar

Well, Java 1.5 rejects manifests with multiple class path entries!

So I decided to make my own, external manifest file, according to the specification.  I continued the line with single spaces. This failed. After more attempts, I went back to the Web and discovered this post:

Oh, and another thing. For multiple lines, use two spaces not one...because the single space is removed when concatinated.

Ning & Stealth mode

(originally posted here on 20 Jan 2006)

Last Friday, Mike and I were chatting about how no compelling applications came out of Ning. We agreed that it was because of their silly committment to stealth mode during their gestation. You don’t publicly reveal your early development because it’s “so web 2.0″. You do so to get an early reality check on whether or not your project sucks.

Knowledge is good, but better than knowledge is a good epistemology that allows the rapid and timely acquisition of knowledge! You can teach a man to fish and he can feed his family, but if you teach him how to teach himself to fish…

Anyway, TechCrunch mentioned Ning today, listing four problems why the service isn’t taking off.

But the reality of Ning is that it’s lost whatever coolness it had, no one uses it and Ning is going to have a very hard time getting people’s attention when they finally do roll out better functionality. Here’s are the problems….

And in other Stealth Mode news, Ookles just closed its Angel round in Om Malik’s bathroom. Ookles? That’s for them to know, and us to buzz, buzz, buzz, about! Let’s get all excited and see what clues we can scrape up from google searches and reverse DNS lookups! Or not.

So the other problem with stealth mode, closely related to the first, is that operations that grow organically are stronger than ones designed in one afternoon around a table. This is the insight behind Agile software development, and ultimately is the lesson of the Vietnam War as well. A few days ago I noticed that blogger’s search stinks, and I’d like a tiny tag cloud in the sidebar of my blog. I could write a scraper but where would I host it? I realized there was a need for a new type of service, where I could upload some little script somewhere, tell the service to run it nightly, and point a sidebar of my blog to its output. I should put up a J2EE app server somewhere, maybe at toys.pokkari.tv. I could write a little administration app that allows uploading and deployment of ear files. And then, to accomodate those who wanted to write in other languages, I could drop in the Bean Scripting Framework and many language libraries. And some other page parsing and manipulation libraries to make work on web pages less like DOM and more like Chickenfoot. Eventually it would grow into something very easy to use, under the guidance of real users and real usage.

Update 15:13 ET:

I’ve never written an app on Ning because PHP is not my bag. Check out I Am Alpha, and Zoho Creator.

log4j.xml inside your jar

(originally posted here on 24 Jul 2005)

Ever wonder how to ship a jar with a log4j.xml inside it? In the jar’s main class, use

static // loads before anything else can
{
   /*
    * If log4j.configuration system property isn't set,
    * then assume I'm inside a jar and configure
    * log4j using the config file that shipped in the jar.
    */
   if (System.getProperty("log4j.configuration") == null)
   {
      URL url = ClassLoader.getSystemResource("log4j.xml");
      DOMConfigurator.configure(url);
   }
}

A pathway to many abilities some consider unnatural

(originally posted here on 08 Jul 2005)

You know you want it.

The data starts dumb: a piece of plain text or a configuration file ending in .rc, .properties, or .ini. They are only simple lists with the most basic form of structure; the name/value pair. But that trivial step begins the enrichment process. Special sectioning codes may then be added. Perhaps comments are introduced to allow authors to enter notes to each other which the parser ignores. If the size of the document grows large enough, and values are repeated, the humans editing them get sick of using search and replace, and the specification expands to include some sort of variable. Once variables exist, it’s a short step to try to use them for conditionality so sections of the document are activated only if a variable is set to a certain value. Inclusions seem reasonable to support, allowing common functionality to be separated into commonly invoked files instead of requiring that each file stand independently.

Further usage will be eased by introducing looping mechanisms to eliminate the pointless repetition of large sections of content that differ slightly or not at all. And once loops are available, one already has a simple scripting language. At this point the pretense of the declarative format is dropped, and efforts to add power to the language are regarded as improvements. It might start to distinguish text from numbers, it might gain access to network or Operating System features.

If the new format is taken seriously, larger projects are created and require maintenance. The solutions depend on the era: the goto command could be censored for the ideal of Structural Programming, code could be isolated in objects that model real-world things, or, concerns could be isolated into interwoven aspects. Now this format — which began as a configuration file format — is a real programming language.

Perhaps no single entity has made the entire journey from properties file format to programming language, but there is a constant pressure towards greater expressive power. Real languages have evolved from rather humble beginnings. Macro lists for IRC clients have become scripting languages capable of authoring 200K applications. Microsoft Word’s scripting language only needed to introduce some small intelligence into text documents, but ended up as a layer with the capacity to support viruses. Linux firewall configuration files already support variables and simple execution flow control.

There are only two forces pushing in the opposite direction. With added power comes added complexity, and many scripting and programming languages are beyond the capability of the uninitiated. And, more complex languages often require processing steps between source and executable. But these are the only reasons. The final encoding for any information is a real programming language. The most advanced and general way to report the number “5″ is to cut to the chase past all intermediate stations and implement a method, in an object oriented language, which returns the integer value of 5.

“5″ wants to be code, and ultimately it will.