I regret using Java Web Start for this project. It is not extensible, reliable, or user-friendly enough to support even my small application used by mostly computer nerds.

Java Web Start doesn’t work for a large number of users

Every semester I get about 10 posts to the program’s message board by people who can’t run the scheduler. I usually go through the process of looking through error logs and clearing caches and usually it doesn’t work, and these people simply cannot run the scheduler. These people all have the latest version of Java installed.

I imagine that most people who can’t get it working don’t post to the message board. Even if 1 in 4 post to the message board, that’s 40 out of a few thousand students, around 1-2%, who can’t run the scheduler at all.

Users don’t like the experience

Long ago, the scheduler used to be an applet. I get feedback from people saying they liked it better as an applet. I guess it’s for the same reasons that people like webmail: there’s zero setup, zero configuration, very short wait before it launches.

Java/JWS detection in the browser is necessary, and unreliable

To provide a good user experience you need to detect JWS and Java in the browser, so you can ask the user to download Java if they need to. There’s not an easy way to detect reliably from the browser. I use a hacky VBScript+Javascript combination from a Sun tutorial, which worked with some modifications. It only works well on Windows with IE. I had to make a page saying “If you think you have Java installed, click here” and so on, which a large percentage of users see (including all Linux and Mac users).

Users don’t know what JNLP files are

Users were confused about JNLP files. Users know what .exe files are, but not little 0.5kb JNLP files. Even if JWS is installed, Firefox users see this silly dialog asking whether to open or to save. The JNLP file on the user’s desktop does not have your application’s icon, it has a generic java icon (if Java is installed).

You cannot make the user experience much better

JWS does not allow your application installation and startup to look and feel smooth. On OSX, you might see several dock icons appear and disappear during startup. Some of them are Java icons, some are yours. There’s no way around this. Also, users are forced to see the ugly JWS download/install screen. You can minimize the visibility of this screen by using an “installer”-type JNLP file which only downloads a small installer jar.

If you want to put your application in the Start Menu or desktop, your users will see a disgusting, confusing dialog asking about “enabling desktop integration.” Most users click No, but I asked around, and many of those who clicked No said they would like to add the scheduler to the start menu, they just didn’t think it was possible. These people are Computer Science students.

The only reasonable solution is native launchers

I think the only reasonable solution for Java client deployment is to deploy native binaries (.exe, .app in .dmg, .rpm/.deb) which embed the JRE, or requires the JRE to be installed, or embeds the JRE installer in the application or in the app’s installer.

I prefer embedding the JRE because then you can have a single download page per platform and you know that it will work.

UPDATE: Kyle Cordes has posted some similar thoughts on Web Start.

For a simple XML schema which defines 8 elements, the JAXB compiler generates 45 Java classes spread over 3 packages. To use the classes, I need to include 7 jar files in my application.

I’m going to stick to the DOM.

The table is here: Eclipse 3.2 M4 - Old and Already Implemented.

UPDATE: people are discussing this table at this JavaLobby thread.

I’ve learned a lot about XSLT today to produce a list of group and action ID’s built into IntelliJ IDEA. It is located here:

IDEA Built-In Action ID’s

I just now came across the new ProcessBuilder class in Java 5, with methods like redirectErrorStream(boolean) and environment() which should be a setter and a getter, respectively.

It’s harder and less pleasant for me to read my own code when using these classes. I hope Sun engineers will stop knowingly making Java code uglier in future releases.

Are you a slave to hot swap? Do you avoid renaming, extracting, or changing modifiers of methods so you can reload the classes? How do you get around it?

• Show posts from a set of newsgroups in one list
• Download all new posts immediately, so I don’t have to wait half a second to view each message
• Show threads in one big nested page, like web forums
• Show new message count in the dock, like Mail or Thunderbird do for mail messages

I’ve never used a newsreader that does all of these things, and I’ve never even seen one that does a few of them. Have you? You should leave a comment below if you know of a reader that I might like.

UPDATE: I have modified my first example code to make the problem clearer.

My problem

I was writing some code today to dynamically insert a large number of HTML elements into the DOM, and give each of them a unique onclick function. My code looked vaguely like this:

[...]
var array = ...
for (int i = 0; i < length; i++) {
  var object = this.createNode()
  var picker = this
  var x = array[i]
  object.onclick = function() {
    picker.select(x)
  }
}

I needed to created a new function for each onclick because each one called select with a different parameter. However, I came across a problem that didn’t make any sense - when I clicked any one of the generated elements on the page, the last onclick function I had created was called. That is, if length was 31, then no matter which element I clicked, select was called with the 31st object in the array.

After hours of debugging and downloading Venkman and searching for information about Javascript closures, I finally found a discussion on the newsgroup comp.lang.javascript, in which Dom Leonard said:

Browser independant code *may not* rely on obtaining a different,
unjoined function object for *any* function declared inside another
function, whether this be because of function declaration or expression
within a loop, across calls to the containing function, or whether the
function be annonomous or named. ECMA 262 both *allows* them to be
different in all cases and *allows* them to share all external
properties (including prototype and user defined properties) in all
cases (because of join operations retaining differences in the scope
chain) and in some cases even *allows* them to be the same function
object without joining.

This was my problem - the browser appeared to be “joining” my function declarations into a single object, instead of creating a new function object for each iteration of the loop.

I’ll provide you with a solution in a minute, but first I have a fun demo for you. What do you think the following code will do?:

<html>
<head>
  <script type="text/javascript">
  function loadme() {
    var arr = ["a", "b", "c"];
    var fs = [];
    for (var i in arr) {
      var x = arr[i];
      var f = function() { alert(x) };
      f();
      fs.push(f);
    }
    for (var j in fs) {
      fs[j]();
    }
  }
  </script>
</head>
<body onload="loadme()"> 

</body>
</html>

If you think it will show alerts “a” then “b” then “c” then “a” “b” “c” again, you’re wrong. In Safari and Firefox, it produces “a”, “b”, “c”, “c”, “c”, “c”. Even though we create the function() in a loop, and x is stored as part of that function’s closure, the same function is used each time, and the closure information is replaced during each iteration.

A solution

I currently use a workaround for this behavior, as described in the comp.lang.javascript discussion. The following code works correctly, producing “a” “b” “c” twice:

<html>
<head>
  <script type="text/javascript">
  function createFunction(x) {
    return function() { alert(x); }
  }
  function loadme() {
    var arr = ["a", "b", "c"];
    var fs = [];
    for (var i in arr) {
      var x = arr[i];
//      var f = function() {
//        alert(x);
//      }
      var f = createFunction(x);
      f();
      fs.push(f);
    }
    for (var j in fs) {
      fs[j]();
    }
  }
  </script>
</head>
<body onload="loadme()"> 

</body>
</html>

However, even this code is not guaranteed to work correctly according to the ECMA spec. I don’t know what is the correct way to do this, according to the spec. If you think you’ve figured it out, please post a comment below.