Trigger an external event
Edit
Don't you dare to close this question! :)
I've to say, that for the Java/MathPackage part of this answer I've used Workbench plugin within eclipse/Juno and again I've to agree with @halirutan that this is not a time saver at all. It took me more time to configure this etc. than to write the code.
I am already a user of the IntelliJ plugin and I have to say decent work gentlemen!
I'm looking forward for more advanced versions for IntelliJ plugin!
If there's anything I can do, just let me know...but this was painful.
Edit end
This might be not the most elegant solution, but why not insert a trigger for your specific table on update/insert which calls one of the extended procedures in ms sql server?
Database side
If now there is an update to your data table your trigger gets fired and the extended procedure (they are all starting with the preamble xp_) is, either touching an external file in order to modify the file timestamp, or is exporting the whole table as a csv file into that specific folder, where your file system monitor is watching/observing.
One specific fine tuning you could do is, that your trigger is (after insert) copying only the new inserted rows/rows which got updated into that file or you create a mirrored table and copy the updated data to this one, from where it is exported.
Mathematica side
On the Mma side you could establish a file system monitor like this:
Begin["subbu`"];
fileName = "/tmp/update"; (* or /tmp/update.csv *)
lastModified = {};
updateQ :=
With[{modificationDate = FileDate[fileName, "Modification"]},
If[
lastModified == modificationDate,
False,
lastModified = modificationDate; True
]
];
task = CreateScheduledTask[
If[updateQ, Print["Changed"], (##1 &)[]], {2, \[Infinity]}];
End[];
You can activate now your file system watcher with:
StartScheduledTask[subbu`task];
....
StopScheduledTask[subbu`task];
The rest is common Mma practice handling external files ...
Hope that this proposal, if not solve your specific problem, but gives you a hint how to achieve the solution you have in your mind.
Edit:
Just for the sake of completeness, since I didn't know that the OP's question was about webMathematica and especially that there is no ScheduledTask support in it.
Here is a JLink version of the answer which should work with webMathematica as well
(Documentation states that it is possible to include external Java libraries). The rest remains, as described above.
At first the Java code:
package de.mma.filesystem;
import java.io.File;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.nio.file.StandardWatchEventKinds;
import java.nio.file.WatchEvent;
import java.nio.file.WatchKey;
import java.nio.file.WatchService;
import java.util.List;
public class DirWatcher {
static String msg;
public static void watch(final File dir) throws IOException {
final WatchService watcher = FileSystems.getDefault().newWatchService();
Path path = dir.toPath();
try {
final WatchKey bDirWatchKey = path.register(watcher,
StandardWatchEventKinds.ENTRY_MODIFY,
StandardWatchEventKinds.ENTRY_CREATE,
StandardWatchEventKinds.ENTRY_DELETE);
new Thread(new Runnable() {
public void run() {
System.out.println("Watching: "+ dir.getName());
while(true) {
try {Thread.sleep(1000);} catch (InterruptedException e) {}
List<WatchEvent<?>> events = bDirWatchKey.pollEvents();
for(WatchEvent<?> event:events) {
System.out.println(dir.getName()+" event: #"+event.count()+","+event.kind()+" File="+event.context());
msg = new StringBuffer(dir.getName()+" event: #"+event.count()+","+event.kind()+" File="+event.context()).toString();
}
}
}
}).start();
} catch (IOException x) {
x.printStackTrace();
}
}
public static String getMessages() {
return msg;
}
public static void main(String args[]) {
try {
DirWatcher.watch(new File("/tmp/test"));
} catch (IOException e) {
e.printStackTrace();
}
}
}
And here's the Mathematica package:
BeginPackage["FileWatcher`", {"JLink`"}]
RegisterDir::usage = "RegisterDir "
GetMessage::usage = "GetMessage "
DisplayDebugConsole::usage = "DisplayDebugConsole "
Begin["`Private`"]
(* you can do this here or in your notebook environment...however *)
ReinstallJava[CommandLine -> "/usr/bin/java"];
AddToClassPath["where the directory with the class files located"];
LoadJavaClass["de.mma.filesystem.DirWatcher"];
Clear[RegisterDir]
RegisterDir[directory_String] :=
Module[{},
DirWatcher`watch[JavaNew["java.io.File", directory]]
]
Clear[GetMessage]
GetMessage[] := DirWatcher`getMessages[]
Clear[DisplayDebugConsole]
DisplayDebugConsole[] :=
JavaBlock@Module[{cw},
LoadJavaClass["com.wolfram.jlink.ui.ConsoleWindow"];
cw = ConsoleWindow`getInstance[];
cw@setLocation[100, 100];
cw@setSize[450, 400];
cw@show[];
cw@setCapture[BitOr[ConsoleWindow`STDERR , ConsoleWindow`STDOUT]];
]
End[]
EndPackage[]
You don't really need a special written package, since the Java code has such a simple interface.
With this you can register directory paths (that path, which contains the file you are writing from your trigger procedure in your database) and you'll get the specific events from DirWatcher.
Using it is extremely simple:
<< FileWatcher`
DisplayDebugConsole[] (* handy tool to see stderr, stdout messages from jvm *)
RegisterDir["/tmp/test"] (* the directory you are observing *)
GetMessage[] (* if nothing is in the queue it is Null, otherwise it will display the specific event that did happen on a specific file inside the directory *)
You could trigger GetMessage after some equidistant interval.
Sorry for the late additional answer, but with this temperatures here I incline to have a south-spanish working attitude ;) Siesta!
