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Java's File.renameTo fails on Windows

February 2nd, 2010

I had a problem with renaming a properties file. Java’s File.renameTo() always failed and returned false. There was no explanation as to why it failed, so it left me stuck with no idea what to do.

Windows has a different file locking policy to Unix (and everyone else). Under Windows, if a process has a file open no other process can rename, move or delete the file until that process has closed all handles to it. As if that wasn’t bad enough, if you do leave a file open and your code finishes running the file will still be locked after an unknown amount of time. It could be 30 seconds or it could be never. Hurray for windows :(

So you must ensure that the file you are trying to rename is completely closed. My problem turned out to be in the loading and saving of properties files. Almost all the example code you download relating to reading and writing properties is wrong. Properties.load() and Properties.store() both take file streams. If the stream is still open then the file will be locked.

Most of the examples tell you to load the properties like this:

Code

Properties properties = new Properties();
properties.load(new FileInputStream("filename.properties"));

and save them like this:

Code

Properties properties = new Properties();
properties.store(new FileOutputStream("filename.properties"));

I was under the impression that store and load closed down the stream after they had done their business, but this is not the case. The streams are left open. So when you use the methods above to create a file and read from a file you are leaving the handle open. What’s worse is that because the FileInputStream and FileOutputStream are in-line there is no reference available to close the streams down - and you are stuffed!

The correct method of reading from a Properties file is:

Code

FileInputStream in = null;
Properties properties = new Properties();
try
{
  in = new FileInputStream("file.properties");
  properties.load(in);
}
finally
{
  if (in != null) in.close();
}

and similarly, writing to a Properties file:

Code

FileOutputStream out = null;
Properties properties = new Properties();
try
{
  out = new FileOutputStream("file.properties");
  properties.store(out);
}
finally
{
  if (out != null) out.close();
}

Now, after reading and writing, you have explicitly closed the file and you are free to rename the file without error.

Automatically showing the Editor's file in Eclipse's Package Explorer

January 28th, 2010

Searching on Google can be really easy as long as you pick the right words to search for. What if you’re not sure what you are looking for or what if you don’t know what the thing (or action) is called?

I was using Eclipse (the Java language editor) in its vanilla form and when I switched to Spring Tool Suite (STS) (which is a re-badged version of Eclipse) I found that the feature I thought was so useful had been switched off.

I knew the feature I wanted to switch on but I didn’t know what it was called! So I’m writing this article so that others might find it and not have to spend 2 weeks looking for it.

When the Eclipse feature is switched on, selecting a file to edit will open the representation of the file in the Package Explorer pane. As you open more files and switch to them in the editor pane, the focus moves in-line inside the Package Explorer.

This is called Linking or Link with Editor. You are linking the Package Explorer with the Editor pane. There is a double arrow icon at the top of the Package Explorer that toggles this behaviour:

Integrating a better file comparer than clearcase offers

January 26th, 2010

Wonderful though Clearcase is, its support tools leave a lot to be desired. Take the file comparison application that comes bundled. It only flags lines which have changed, so you often have to spend a couple of moments scanning the line to spot the changes. There are loads of file comparers out there to choose from. So here is how to integrate it with Clearcase.

The simplest way is to find a file comparer with Clearcase integration capabilities like KDiff3. The integration is simple:

  1. Download KDiff3 and install.
  2. Run it up.
  3. From the menu select Settings->Configure KDiff3.
  4. Go into the Operation tab.
  5. Click Integrate with Clearcase.
  6. Click Ok.

Simple, but what if your file comparison tool doesn’t have an integrate with Clearcase button? Changing the Clearcase hooks is quite straight forward. The mapping file exists in:

<installation-root>\ClearCase\lib\mgrs\map

The file is keyed in extension (or class) and action, so replace the following lines in the map file.

_rftdef            xcompare  C:\Program Files\KDiff3\kdiff3.exe
_rftmap            xcompare  C:\Program Files\KDiff3\kdiff3.exe
_rftvp             xcompare  C:\Program Files\KDiff3\kdiff3.exe
_xml               xcompare  C:\Program Files\KDiff3\kdiff3.exe
_xml               xmerge    C:\Program Files\KDiff3\kdiff3.exe
_xml2              xcompare  C:\Program Files\KDiff3\kdiff3.exe
_xml2              xmerge    C:\Program Files\KDiff3\kdiff3.exe
_xtools            xcompare  C:\Program Files\KDiff3\kdiff3.exe
text_file_delta    xcompare  C:\Program Files\KDiff3\kdiff3.exe
text_file_delta    xmerge    C:\Program Files\KDiff3\kdiff3.exe
whole_copy         xcompare  C:\Program Files\KDiff3\kdiff3.exe
whole_copy         xmerge    C:\Program Files\KDiff3\kdiff3.exe
z_text_file_delta  xcompare  C:\Program Files\KDiff3\kdiff3.exe
z_text_file_delta  xmerge    C:\Program Files\KDiff3\kdiff3.exe
z_whole_copy       xcompare  C:\Program Files\KDiff3\kdiff3.exe
z_whole_copy       xmerge    C:\Program Files\KDiff3\kdiff3.exe

Finding which files are on a clearcase branch without a label

January 25th, 2010

The clearcase reports that come out of the box only let you find out the files that have changed between 2 labels. What if you haven’t applied the other label yet, or you are writing release notes and the official labelling hasn’t taken place yet?
If you have applied a label, how do you know which files have changed since then.

Open a command line and switch to the view and directory path you are interested in. Issue the following command:

cleartool find . -cview -version “!lbtype(MY_LABEL)” -print

where:
‘.’ is from the current directory,
-cview is current view
-version “!lbtype(MY_LABEL)” is look for versions without a label called MY_LABEL
-print is what to do with them.

What is Project Voldemort? What is Voldemort?

January 4th, 2010

Seems like an honest question, however the Project Voldemort website doesn’t actually tell you. Their page describes what features it has but doesn’t explicity say what it is. The Project Voldemort web site doesn’t have any email address of any of the members to ask questions, it only has an mailing list to which you can post questions.

After a bit of hunting, in fact far more hunting that I would have expected I came across this article which explains what Voldemort actually is. It even mentions why the project is called Project Voldemort.

http://www.bigdatabaselist.com/wiki/Project_Voldemort

Prehaps they should read my article on clearly defining what a project does. “The whats and whys to creating project descriptions“.