Develop Reference

Files delete() method in Java is not working

Not able to delete the file001.txt which is created in my local dir path by using the removeFile(s) method in switch case. Then the method removeFile(s) calls the class Employee_Remove, where file.delete() method does not delete the files. Please find the below 2 codes and also screenshot.
I don't want to create duplicate or renaming the filename. I just need to delete the files which is created in my local dir. I did not understanding the problem whether it code problem or Eclipse problem.
Can anyone help to solve the issue.
case 3:
{
System.out.print("\nPlease Enter Employee's ID :");
String s=sc.nextLine();
Employee_Remove epr =new Employee_Remove();
epr.removeFile(s);
break;
}
class Employee_Remove {
public void removeFile(String ID) {
File file = new File("file" + ID + ".txt");
if (file.exists()) {
if (file.delete()) {
System.out.println("\nEmployee has been removed Successfully");
}
} else {
System.out.println("\nEmployee does not exists :( ");
}
}
}

If you get no output to the Eclipse console window, that means that:
Your application code has found the file. If it didn't find it, you would get a message.
The file was not deleted. If the delete had succeeded, then you would get a message to say so.
It is not clear why your application found the file but did not delete it deleted. One possibility is that your application does not have permission to delete the file. A second possibility is that something else has the file open. On Windows that locks the file, and that would prevent the application from deleting it. (There are some other more obscure causes, but I doubt that they would be applicable here ...)
If you want to get diagnostics that explain give more information about why the file wasn't deleted, switch to using the newer java.nio.file.* APIs; e.g. java.nio.file.Files::delete(Path).
If the output is NOT as you described, then it is possible that the application DID delete the file (and said so) but Eclipse has not noticed. In my experience Eclipse does not notice changes made to files that were not made by Eclipse itself.
If this is the case, then doing an Eclipse refresh should update the view. The Eclipse shortcut for this is typically F5 or CNTRL-F5, but check the key bindings.

How to have only one instance of the CHM file opened?

I want to set up only one instance of the CHM file when clicking on "Help" in the menubar and stopping it from opening twice when clicked again - therefore how do I code it?
I've tried to use it with process.isAlive(), but after I close it I want a counter set to zero, which only opens another CHM file when the counter is 0.
helpMenu.addMouseListener(new MouseAdapter() {
// do this after clicked
openCHM();
});
So MouseEvent is fired once.
openCHM() {
Process p;
if(cnt == 0) {
p = Runtime.getRuntime().exec("hh.exe Help.chm");
cnt++;
if(!p.isAlive()) {
cnt = 0;
}
}
I expected the counter to be 0, but then came to the conclusion that MouseEvent already fired once and the code got already executed, therefore it never goes to the second if-statement and sets my counter to 0.
EDIT
There is no correct answer how to open a CHM file once, but there is a workaround that makes it possible, we just need to look if the file is renamable or not.
protected void openCHM() {
try {
File file = new File("YOURNAME.chm");
boolean renamable = file.renameTo(file); // can't rename if file is already open, returns true if renaming is possible
if(renamable) {
Runtime.getRuntime().exec("hh.exe YOURNAME.chm");
} else if(!file.exists() ){
// message: file doesn't exist (in path)
} else {
// file is already open
}
} catch () {
}
}

I'm not a Java programmer but the short story - not possible (AFAIK).
You know, hh.exe is the HTMLHelp executable and associated with *.CHM files. It's just a shell that uses the HTML Help API and is really just hosting a browser window.
HH.EXE is not single instance, if you open a CHM or another file three times using HH.EXE, then three help windows will appear. Try it using PowerShell:
PS D:\_working> hh.exe C:\Windows\Help\htmlhelp.chm
Several client-side command line switches are available to help authors that are part of the HTML Help executable program (hh.exe) and therefore work when HTML Help Workshop is not set up.
KeyHH.exe was running years ago with special parameters.
If you call the HH API directly from your application, and not via a second helper program like HH.EXE or KEYHH.EXE, then you MUST close any open help windows before shutting down the application or you will probably crash Windows.
For some information related to the problem you maybe interested in Open CHM File Once.
Some quoted info from the link above:
When you do that you are just calling the help viewer again and again from the command line, you're not using the HTML Help API which is what you need to access the CHM once it is open. You need to check whether your flavors of Java and Smalltalk support calls to the HTML Help API. This API is documented in detail in the help file of Microsoft HTML Help Workshop, which is the compiler package you installed to be able to generate CHMs.

Issue with running JAR from Desktop, but not from command line or Eclipse

I am running into a peculiar issue (peculiar for me anyways) that seems to happen in a SwingWorker that I use for saving the result of another 'SwingWorker' thread as a tab-delimited file (just a spreadsheet of data).
Here is the worker, that initializes and declares an object which organizes the data and writes each table row to a file (using BufferedWriter):
// Some instance variables outside of the SwingWorker:
// model: holds a matrix of numerical data (double[][])
// view: the GUI class
class SaveWorker extends SwingWorker<Void, Void> {
/* The finished reordered matrix axes */
private String[] reorderedRows;
private String[] reorderedCols;
private String filePath; // the path of the file that will be generated
public SaveWorker(String[] reorderedRows, String[] reorderedCols) {
// variables have been checked for null outside of the worker
this.reorderedRows = reorderedRows;
this.reorderedCols = reorderedCols;
}
#Override
protected Void doInBackground() throws Exception {
if (!isCancelled()) {
LogBuffer.println("Initializing writer.");
final CDTGenerator cdtGen = new CDTGenerator(
model, view, reorderedRows, reorderedCols);
LogBuffer.println("Generating CDT.");
cdtGen.generateCDT();
LogBuffer.println("Setting file path.");
filePath = cdtGen.getFilePath(); // stops inside here, jumps to done()
LogBuffer.println("Path: " + filePath);
}
return null;
}
#Override
protected void done() {
if (!isCancelled()) {
view.setLoadText("Done!");
LogBuffer.println("Done saving. Opening file now.");
// need filePath here to load and then display generated file
visualizeData(filePath);
} else {
view.setReorderOngoing(false);
LogBuffer.println("Reordering has been cancelled.");
}
}
}
When I run the program from Eclipse, this all works perfectly fine. No issues whatsoever. Now I know there have been tons of question on here that are about Eclipse running fine while the runnable JAR fails. It's often due to not including dependencies or referring to them in the wrong way. But what's weird is that the JAR also works completely fine when it's being started from command line (Windows 8.1):
java -jar reorder.jar
Et voilà, everything as expected. The CDTGenerator will finish, write all the matrix rows to a file, and return the filePath. With the filePath I can subsequently open the new file and display the matrix.
In the case of double-clicking the JAR on my desktop, where I placed it when creating it from Eclipse, this is where the program will let me know that stuff happens. I get the error message I created for the case of filePath == null and using some logging I closed in on where the CDTGenerator object stops executing its method generateCDT() (Eclipse debugger also won't reproduce the error and do everything as planned).
What the log shows made me think it's an issue with concurrency, but I am actually leaning against that because Eclipse and command line both run the code fine. The log just tells me that the code suddenly stops executing during a loop which transforms double values from a matrix row (double[]) to Strings to be stored in a String[] for later writing with BufferedWriter.
If I use more logging in that loop, the loop will stop at a different iterator (???).
Furthermore, the code does work for small matrices (130x130) but not for larger ones (1500x3500) but I haven't tested where the limit is. This makes it seem almost time dependent, or memory.
I also used jVisualVM to look at potential memory issues, but even for the larger matrices I am on ~250MB which is nowhere near problematic regarding potential OutOfMemoryExceptions.
And finally, the last potential factor I can think of: Generating the JAR 'fails' due to some classpath issues (clean & rebuild have no effect...) but this has never been an issue before as I have run the code many many times using the 'broken' JAR and execute from Desktop.
I am a real newbie to programming, so please point in some direction if possible. I have tried to find logged exceptions, logged the values of variables, I am checking for null and IndexOutOfBound issues at the array where it stops executing... I am at a complete loss especially because this runs fine from command line.

It looks like the problem had to see with the java versions installed in OP's computer. They checked the file extensions and the programs associated to each one in order to see if it was the same java version as executed from Eclipse and the command line.
Once they cleaned older java versions the jar started to work by double-clicking it :)

Cause I do not have enough points (need 50 to directly answer your question), I need to ask this way:
If you double click a JAR you won't see a console which is often the problem because you can't see stack traces. They get just written to "nowhere". Maybe you get an NPE ore something else.
Try to attach an Exceptionhandler like this Thread.setDefaultUncaughtExceptionHandler(UncaughtExceptionHandler) and let this handler write down a message to a file or such...
Just an idea.

Eclipse RCP: File association (--launcher.openFile)

I'm developing an eclipse product and i need to associate a file extension to my editor.
I followed several examples (as like as this and
this) but it seems that the editor ever receives the SWT OpenDocument event.
As described in the fileAssociation example i created an eventListener class to process SWT.OpenDocument events and i added this in my Application class to the display before that the PlatformUI.createAndRunWorkbench() method gets called
public Object start(IApplicationContext context) throws Exception {
Object args = context.getArguments().get(IApplicationContext.APPLICATION_ARGS);
OpenDocumentEventProcessor eProc = new OpenDocumentEventProcessor();
Display display = PlatformUI.createDisplay();
display.addListener(SWT.OpenDocument, eProc);
try{
if(!handleWorkspace(display)){
System.exit(0);
return IApplication.EXIT_OK;
}
int returnCode = PlatformUI.createAndRunWorkbench(display, new XVRWorkbenchAdvisor(args, eProc));
In the product file i added the following program arguments:
--launcher.XXMaxPermSize
256m
--launcher.defaultAction
openFile
-name
XVR Studio Developer
If I use the same code in a new empty RCP project it works like a charm..
I can't figured out which could be the problem..
can you help me?
Thanks a lot!!

This approach is unknown for me, but since there is no explicit editor call in your pasted code I guess you still rely on eclipse to decide which editor has to be opened. So I guess you still have to define contentypes and file associations declaratively. To do that contribute to "org.eclipse.core.contenttype.contentTypes" extension, add a 'file-association' (file extension...). Get your editor declaration in your plugin xml and add the previously created 'contentTypeBinding' id.

As I have just made this work for an RCP app, I thought it would be helpful to document how I did it here, and provide refs.
I had no use for the 'context.getArguments()..', the 'OpenDocumentEventProcessor' handled everything.
I would suggest that the reason this did not work was that the -name value did not match the value of the 'appName' property in the 'org.eclipse.core.runtime.products' extension point. Just to be sure, I removed the spaces from the appName property and in the -name. Then it worked.
Very useful references are:
For the basic coding:
http://help.eclipse.org/indigo/index.jsp?topic=%2Forg.eclipse.platform.doc.isv%2Fguide%2Fproduct_open_file.htm
For an explanation of how this works:
http://aniefer.blogspot.co.uk/2010/05/opening-files-in-eclipse-from-command.html
One small point that eluded me for some time, was getting the path for the file in several chunks at the place where there was a space in the name. Eventually I realised (in a 'duh!' moment) that I needed to put quotes round the %1 parameter in the installer's (InstallAware) definition for the file association - i.e it became "%1"

lazily compile JasperReports .jrxml to .jasper

I use Jasper reports with the JasperReportsMultiFormatView class provided by the Spring framework. This class takes care of compiling the source .jrxml files to their compiled .jasper format when the Spring application context is created.
However, this compilation process is really slowing down the application startup time. Is it possible for the reports to be lazily compiled instead of compiled at startup time, i.e. a report is only compiled the first time it is requested?
If this is not possible, alternative suggestions for how I can reduce/eliminate the report compilation time would be welcome. Of course, I could mandate that the compiled reports must be checked into SVN along with the .jrxml files, but it's only a matter of time, before someone (most likely me) forgets.
Cheers,
Don

I, like you, started out with the Spring helper classes for Jasper Reports but quickly abandoned them as being too coarse-grained and inflexible, which is unusual for Spring. Its like they were added as an afterthought.
The big problem I had with them was that once they were compiled, it required an appserver bounce to put in new versions. In my case, I was after a solution whereby I could change them on disk and they'd recompile, much like how JSPs normally work (if you don't turn this feature off, which many production sites would).
Alternatively, I wanted to be able to store the jrxml files in a database or run the reports remotely (eg through the JasperServer web services interface). The Spring classes just made it all but impossible to implement such features.
So my suggestion to you is: roll your own. There are a couple of gotchas along the way though, which I'll share with you to minimize the pain. Some of these things aren't obvious from the documentation.
The first thing you'll need is a jasper reports compiler. This is responsible for compiling a jrxml file into a JasperDesign object. There are several implemenations of this but the one you want is the JRJdtCompiler. You can instantiate and inject this in a Spring application context. Avoid others like the beanshell compiler since running the report as a large beanshell script is not particularly fast or efficient (I found this out the hard way before I knew any better).
You will need to include the jar files for the JRJdtCompiler. I think the full Jasper Reports dist includes this jar. Its an eclipse product.
You can store the JasperDesign anywhere you like (HttpSession, servlet context or whatever). The fillReport() method is the primary one you're interested in. It creates a JasperPrint object, which is an instance of a run report. Parameters are just passed in as a Map.
Now to create a versino in HTML, PDF, etc, you need to export it. You use classes like the JRHtmlExporter and JRPdfExporter to do this. They require certain parameters. The tricky one is the HTML exporter because HTML obviously doesn't include the images. Jasper includes an ImageServlet class that fetches these from the session (where the JRHtmlExporter has put them) but you have to get the config of both the HTML exporter and image servlet just right and its hard to tell where you're going wrong.
I don't remember the specifics of it but theres an example of all this in the Jasper Reports Definitive Guide, which I'd highly recommend you get if you're spending anytime at all with this product. Its fairly cheap at US$50. You could get the annual subscription too but in the 18+ months I've seen it I haven't seen a single change. Just buy the new version when it comes out if you need it (which you probably won't).
Hope this helps.

The report is compiled the first time its run, put a break point in AbstractJasperReportsView protected final JasperReport loadReport(Resource resource) method to confirm this.
However the above post is correct that you'll need to extend the JasperReportsMultiFormatView if you want to provide any specific compilation process.
A great example of dynamic compilation is here: http://javanetspeed.blogspot.com/2013/01/jasper-ireport-with-java-spring-and.html
import net.sf.jasperreports.engine.JasperReport;
import org.apache.log4j.Logger;
import org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView;
public class DynamicJasperReportsMultiFormatView extends JasperReportsMultiFormatView {
private static final Logger LOG = Logger.getLogger(DynamicJasperReportsMultiFormatView.class);
/**
* The JasperReport that is used to render the view.
*/
private JasperReport jasperReport;
/**
* The last modified time of the jrxml resource file, used to force compilation.
*/
private long jrxmlTimestamp;
#Override
protected void onInit() {
jasperReport = super.getReport();
try {
String url = getUrl();
if (url != null) {
jrxmlTimestamp = getApplicationContext().getResource(url).getFile().lastModified();
}
} catch (Exception e) {
e = null;
}
}
#Override
protected JasperReport getReport() {
if (this.isDirty()) {
LOG.info("Forcing recompilation of jasper report as the jrxml has changed");
this.jasperReport = this.loadReport();
}
return this.jasperReport;
}
/**
* Determines if the jrxml file is dirty by checking its timestamp.
*
* #return true to force recompilation because the report xml has changed, false otherwise
*/
private boolean isDirty() {
long curTimestamp = 0L;
try {
String url = getUrl();
if (url != null) {
curTimestamp = getApplicationContext().getResource(url).getFile().lastModified();
if (curTimestamp > jrxmlTimestamp) {
jrxmlTimestamp = curTimestamp;
return true;
}
}
} catch (Exception e) {
e = null;
}
return false;
}
}