Recursively delete a directory, emptying all contents.

A handy class I use all the time to encapsulate the idea of whether two events coincide. For example, given a time period representing a shift, and a list of time periods representing transactions or sessions or whatever, find which ones are either totally or partially within the time period. This class make it a bit easier.

Do you find yourself implementing toString on your objects all the time, and wondering why (the debugger seems to do a pretty good job of it all by itself)...well, here's a bit of introspection applied to the problem. This is for all those quick debug sessions where you just want to do System.out.println(myComplexObject).

Instead, just do System.out.println(DebugPrint.toString(myComplexObject));

Here's a nifty trick I often use for testing.

Lets say you have a c:\foo\lib directory full of jarfiles for log4j, javamail...whatever.

Modern J2EE containers do a nice job of letting you deploy a jarfile with your code and have a lib directory full of jarfiles like this, but what if you just want to run a quick client from the command line?

Here's what you do:

Reading and writing to a URL connection, thanks to Java.

Another way to generate a unique ID.

This is a correct way to do login form auto-focus, checking to see if either username or password have focus already. This prevents someone from typing a username hitting TAB, then having JavaScript chime in, resetting focus to Username while user is typing in their password. In this case, the password is appended to the username which is in plaintext.

Another solution recommends using a text match pattern.
This works, but as long as you've got mail.jar in your classpath anyway, you might as well use this technique instead. (Plus, I think it works with older JDK 1.2+, whereas pattern.compile is 1.4+)

Note that it also accepts a comma-separated list of emails, just like a To: or CC: address line would.

Java properties files can yield undesirable results at runtime, if there happen to be spaces at the end of some lines.

Requires a win32 port for the GNU utilities grep and sed - e.g. http://unxutils.sourceforge.net/.

if you use the same buildfiles on your local codebase and your continuous integration buildserver, the if-attribute for ant's targets comes in handy...

for this ant buildfile snippet to only create+publish javadoc when executed on the buildserver, the buildserver only has to set the referred system property, e.g. on its startup by using a Java D-option "-Dcontinuous.build=true" ...

ant buildtool website