Brian talked about Subversion at the OCI monthly Java lunch. (I know, it’s not technically a Java topic, but we digress some months). It was a good presentation, although 1 hour is not enough time.

The truth is, I’ve tinkered with Subversion here and there and fully intend to start using it. I currently use CVS at home and StarTeam at work. None of these is an ideal solution, but I believe Subversion will win people over in the long run. I’ve also used Visual SourceSafe at a previous job, as well as ClearCase a long time ago.

I only really heard of two Subversion limitations:

1. The GUIs are not mature - CVS offers good GUIs and tight integration with IDEs. The Subversion IDE integrations are crude in comparison
2. Subversion offers no exclusive locking scheme, which is essential in some environments. Don’t get me wrong, I prefer the concurrent editing mode of CVS and Subversion. However, many organizations store lots of big binary files in version control - like Word docs. Merging those kinds of files is either impossible or a pain, at best. Plus, some companies just won’t let you use a tool that does not support exclusive locking. Argue the merits of this if you will, the fact is that some companies just work that way. I heard that exclusive locking will be included in a future release, so it will not be a problem for long.

Subversion has a rock solid version control infrastructure under the covers. Here are some features that many other version control tools - surprisingly - don’t have:

• The ability to version directories.
• The ability to re-add files after you delete them, preserving the old history. StarTeam, for example, cannot do this.
• An efficient branching and merging model.
• Every operation is versioned - things like moves, copies, deletes, etc…
• You can attach arbitrary attributes to any file, which is great for linking files to defects, for example.

Things like first-class GUIs and IDE integrations will be available for Subversion. It will take some time to catch up to CVS, but Subversion will catch up.

Version 4.5 of the best Java IDE was released today. The biggest new feature? IDEA now supports JDK 1.5 syntax.

Related link: http://www.bestpractical.com/rt/

Boy, I thought RT helped me out in my work, but my experience is nothing compared to this. Jesse Vincent is giving a tutorial on customizing RT here at OSCon, and as an aside he mentioned that a German peer-counseling group is using RT to track incoming emails from people in need of counseling. The group has customized RT so that if an email is sent in containing the words “suicide” or “kill myself,” the counselors get an immediate pager alert. I’m quoted on the RT praise page as saying I’d be screwed without RT; and the quote below mine says “RT *saved my life*.” It’s amazing how literally those words are true in Jesse’s anecdote.

Has software you’ve written ever saved a life?

Related link: http://www.apple.com/downloads/macosx/development_tools/mono.html

I’m a Java and AspectJ developer at heart but, never one to ignore a programming language or technology, I’ve been playing with Mono on my Windows box at home when I was sent away on business with just my powerbook. Don’t get me wrong, I prefer the p’book anyway but I was playing with C# at the time and I could remember the all-too-recent pain I’d gone through getting mono onto my home iMac and so I was not relishing the same pain again in getting my new powerbook up to speed.

Then I found out that I needn’t have worried! The kind people at Novell have released a nice and easy way of getting mono onto OS X. It’s been up and available for a while, so my apologies to those out there who are going ‘duh, you’re slow on the uptake’, but I thought it was worth a posting here so that at least if anyone searches in the future then there’s an even better chance that they’ll go straight to the easiest way of getting mono on their mac.

I’m trying to evaluate Macromedia Flash MX just for fun. I never used the product, and the GUI is proving to be quite difficult to learn.

I can generally figure stuff out, but lack of tooltips is driving me nuts. What the #$%^ do these buttons do:

A simple tooltip would likely make these buttons obvious, but half of the buttons in the Flash MX GUI don’t have any tips. No status bar line help, either. Nor do they have the typical “Context Help” toolbar button that would let me click on the button to figure out what it is. To top it off, I cannot even right click on these buttons to figure out what they do. No context menu, nada, zero.

Another gripe - keyboard shortcuts are not consistently displayed. You can right-click on the timeline and select “Insert Keyframe”. The menu does not display the fact that you can also hit F6 to insert the keyframe. How are us hapless users supposed to figure out keyboard shortcuts for all of the other menu items? It sure would be nice to display the shortcuts right there by the menu text, just like a sane person would expect a GUI to do.

My Flash MX evaluation is not getting off to a good start. I’ve spent about an hour tinkering, another 15 minutes writing this blog blowing off steam, and I’ve barely scratched the surface of what this tool is supposed to do.

The most frustrating part? Things like tooltips, context help, and displaying keyboard shortcuts are insanely easy things to add to the GUI. Adding these features to the GUI is trivial, making the tool infinitely easier for newbies. Seems like a no-brainer to me.

Related link: http://www.blogonevent.com/blogon2004/

At the “Publishing Models” session of the BlogOn conference, people are bringing up all the arguments against adoption of RSS. “It’s too techy.” “Publishers will want control of their content.” “It will be too hard to monetize.” “Consumers will not understand what RSS means.”

All of these arguments remind me nearly verbatim of the objections to adoption of the Web ten years ago. http://? Give me a break! Give newspaper content away for free? How will that ever work?

It seems to me that commerce will find a way. I look at the great RSS products, my favorite being Bloglines, and I can clearly see analogous methods for them to become very big businesses, just as Web sites have become commercially successful today — even newspaper Web sites.

Related link: http://www.blogonevent.com/blogon2004/

Halley Suitt: “Rafat, how do you think traditional media is reacting to RSS?”
Rafat Ali: “Traditional media? You mean c|net?”

When obtaining content from websites (either for a server-based app, such as a crawler, or for a client app, such as a newsreader) it’s a good idea to avoid downloading content when possible. Additionally, many if not most servers
support dynamic stream compression, which has a big impact on download speeds, particularly when obtaining text-only
data (e.g., an RSS feed, which if every aggregator did, would help with problems like these). Throughout the Net there are a number of descriptions how to use some of these elements (For example, here is a good guide for conditional GETs, here is one for server-side compression), but I haven’t seen an example of Java client-side code that pulls all the basic techniques together in one place–so here it is.

Basically there are two things to deal with: the first is use of the ETag and Last-Modified headers that allow the server to reply with a 304 (Not modified) response code, thus avoiding altogether download of data we’ve already obtained. The second is that when there is a download, we allow the server to send the content compressed (in GZIP or Deflate –ZLib– formats) to save download time. For text content, compression can reduce the size of the download by a factor of 5 or more.

Without further ado, here’s the code:

...
//create a URL to O'Reilly's Atom feed
URL sourceURL = new URL("http://www.oreillynet.com/meerkat/?_fl=rss10&t=ALL&c=5209");
//obtain the connection
HttpURLConnection sourceConnection = (HttpURLConnection) sourceURL.openConnection();
//add parameters to the connection
sourceConnection.setFollowRedirects(true);
//allow both GZip and Deflate (ZLib) encodings
sourceConnection.setRequestProperty("Accept-Encoding", "gzip, deflate");

// obtain the ETag from a local store, returns null if not found
String etag = loadETag(); 

if (etag != null) {
  sourceConnection.addRequestProperty("If-None-Match", etag);
}

// obtain the Last-Modified from a local store, returns null if not found
String lastModified = loadLastModified();
if (lastModified != null) {
  sourceConnection.addRequestProperty("If-Modified-Since",lastModified);
}

//establish connection, get response headers
sourceConnection.connect();

//obtain the encoding returned by the server
String encoding = sourceConnection.getContentEncoding();

//The Content-Type can be used later to determine the nature of the content regardless of compression
String contentType = sourceConnection.getContentType();

//if it returns Not modified then we already have the content, return
if (sourceConnection.getResponseCode() == HttpURLConnection.HTTP_NOT_MODIFIED) {
  //disconnect() should only be used when you won't
  //connect to the same site in a while,
  //since it disconnects the socket. Only losing
  //the stream on an HTTP 1.1 connection will
  //maintain the connection waiting and be
  //faster the next time around
  sourceConnection.disconnect();
  return;
}

//get the last modified & etag and
//store them for the next check
storeLastModified(sourceConnection.getHeaderField("Last-Modified"));
storeETag(sourceConnection.getHeaderField("ETag"));

InputStream resultingInputStream = null;

//create the appropriate stream wrapper based on
//the encoding type
if (encoding != null && encoding.equalsIgnoreCase("gzip")) {
  resultingInputStream = new GZIPInputStream(sourceConnection.getInputStream());
}
else if (encoding != null && encoding.equalsIgnoreCase("deflate")) {
  resultingInputStream = new InflaterInputStream(sourceConnection.getInputStream(), new Inflater(true));
}
else {
  resultingInputStream = sourceConnection.getInputStream();
}

...

//now the stream can be read directly,
//and the data will be on the contentType received above.

Basically the code sets up the connection and adds the “gzip” and “deflate” encodings as recognized encodings by the app, and if ETag/Last-Modified values exist then they are added to the request with the If-None-Match header for ETag and If-Modified-Since header for Last-Modified, allowing the server to check if the content has changed since that check. If the ETag and Last-Modified are null (that is, this is the first time we are downloading the page) then they are not included in the request.

Once we establish the connection through connect() we check whether the reponse code is “not modified” and in that case we simply disconnect() and return, otherwise we continue by storing the Etag and Last-Modified values returned, and then creating the appropriate wrapper (depending on the content encoding returned by the server) for the network stream so that the content will be decompressed on the fly if necessary.

And that’s it!

PS: the loadETag(), loadLastModified(), storeLastModified(…) and storeETag(…) methods require a persistence layer of some sort (simple Java serialization would do) to access the ETag and Last-Modified values between runs of the application. Since this is heavily dependent on the application, they are not included.

Related link: http://subversion.tigris.org

Building Subversion on Mac OS X is
not hard. Building the Java bindings for
Subversion is challenging until you know what to do. Hopefully you find this
information helpful.

This blog shows how to build Subversion and the Subversion Java bindings. Why?
There are a few reasons you may need the Java bindings:

• You want to write Java code to communicate with Subversion
• You want to use SvnUp, which
  can be installed as a plug-in to
  IDEA

Install Subversion

Before we get started you need to install a
Berkeley DB.
I have version 4.2 installed. They have plenty of documentation to help you.

Step 1

As of today, this is a two step process:

1. Build and install a stable release version (currently 1.0.5) of the client
2. Use the stable release version to checkout the latest source
   from the repository

NOTE: In order to build the Java bindings we need the latest source. Version 1.0.5
does not appear to support building the Java bindings using --enable-javahl and
SWIG does not work.

NOTE: Once version 1.1 becomes stable you should be able
to build the Java bindings using that code base, thus checking out
the latest code is no longer necessary.

NOTE: I was unable to build the Java bindings using
Subversion 1.1 RC1, thus having to build against the HEAD of the
repository. You may have better luck.

Once you have the stable release of Subversion installed use it to download the
latest version Subversion source code from the repository:

  svn co http://svn.collab.net/repos/svn/trunk subversion-tip

Now change to the source directory

  cd subversion-tip

Step 2

Execute autogen.sh

  ./autogen.sh

Step 3

Execute configure

./configure 
  --enable-javahl
  --with-jikes=no
  --prefix=/usr/local/svn-trunk-10351

import org.tigris.subversion.javahl.SVNClient;
import org.tigris.subversion.javahl.Notify;
import org.tigris.subversion.javahl.Revision;

public class SubversionDemo {

    public static void main(String[] args) throws Exception {

        SVNClient client = new SVNClient();

        // The SVNClient needs an implementation of Notify before
        // successfully executing any other methods.
        client.notification(new Notify() {
            public void onNotify(String path, int action, int kind,
                    String mimeType, int contentState, int propState,
                    long revision) {
                System.out.println("SubversionDemo.onNotify");
            }
        });

        // Assume that there is a valid repository with a project called
        // 'freedom'.
        client.checkout("file:///Users/briancoyner/svn-repository/freedom",
                "/Users/briancoyner/MyProjects", Revision.HEAD, true);
    }
}

Exception in thread "main" java.lang.UnsatisfiedLinkError: no svnjavahl in java.library.path
	at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1491)
	at java.lang.Runtime.loadLibrary0(Runtime.java:788)
	at java.lang.System.loadLibrary(System.java:834)
	at org.tigris.subversion.javahl.SVNClient.(SVNClient.java:48)
	at com.briancoyner.subby.SubversionDemo.main(SubversionDemo.java:13)