Wednesday, September 21, 2011

Coding for a new database connection

When I worked for Mellon Bank, a favourite expression of my boss there was "If it ain't broke, don't fix it". I love that expression, and it really applies to what I am doing now.

Now I know you can work in the Collabnet working folder, but I prefer to copy files from there into another working folder, so I can just drag and drop from the original folder into another clean working folder when I stuff up. And because I am a little paranoid, the first thing I do is compile the code, just to make sure nothing strange has happened to prevent it doing so.

In the current version, the main class, AMJApp, makes a call to a function/method in my workhorse class QTrack.

The function call, which actually produces an argument for another local function is as follows:


And the function is:

public String datInsert() {
try {
ItemEntry = "INSERT INTO Items " +
"(Partid, OpCode, Itemdet, Raw, Rate) " +
"VALUES (" +
sessTime + ", " +
OpCode + ", '" +
Itemdet + "', " +
Raw + ", " +
SRate + ")";
buffer = "insert succeeds... ";
} catch(Exception ex) {
buffer = "SQLException: " + ex.getMessage();
return buffer;

Now, I want to minimize disruption, so the first thing I'll do is add another local function, which I shall call addItem3(String newWord). It is initially identical to addItem3(String newWord):

private void addItem3(String newWord) {
if(dbDEBUG) {

I quickly recompile to see if this has destroyed the delicate balance. It hasn't yet, so I make another small change, making the function call:


I have to do this three times in different places in the code. And I recompile again, just to be safe. All OK so far.

My next change is a very subtle one, changing the value returned by the function in QTrack from buffer to ItemEntry. I recompile both classes again, and so far all is OK.

Now comes the crunchy part. I've been putting it off for a long time because I know it will stuff everything up. I have to make the addItem3(String newWord) function do some work. This is the function which will pass the data line to PHP.

I shall borrow the code from a previous post in my Learning Java blog. This code includes a JSObject, and that is why it gets messy. The JSObject requires the import of netscape.javascript.JSObject, which in turn calls on a collection of classes which can be found in a java archive called plugin.jar, while my main class also calls on other classes. So the compile command is no longer a simple javac but rather:

javac -classpath "C:\Users\MJHIPP\Documents\Current\Java\CodeLocal\AMJ110920\plugin.jar";"."

I recompile again just to be safe, and then to be ultra safe I simply add the import line before recompiling with the new command. There was a bit of fiddling around, because that class path is a bit of a fiddle, but that is why I like to recompile after every small step. I can cope with one error, but not a whole screen full.

The next small step is to add the JSObject, and I put it right at the beginning, with my other supporting class declarations. Another recompile and all is still OK. Finally I have to add code to the addItem3(String newWord) function:

private void addItem3(String newWord) {
if(LIVE) {
if(jso != null )
try {"updateWebPage", new String[] {newWord});
catch (Exception ex) {

The modified class compiles just fine, but I now realise a fatal flaw in my methodology. I complied at every step but I did not check to see that the modified Applet actually ran. I was therefore very disappointed when it did not.

After some discussion on the Java Applet development forum it seemed to have something to do with JDK versions. And after fiddling for a while with cross-compilation options, I removed everything to do with Java from my computer, installed JDK 6.27, and recompiled, and now the new Applet runs.

It's not posting data yet, but hopefully that is a small diagnostic problem, to be fixed another day.

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