How do I get a stack trace in a String?
It comes up every now and then: someone wants a stack trace in a String. They're probably wrong; if they're trying to analyze the stack trace, there are mechanisms in the Throwable to do that without creating a String and parsing it, but just in case... here's how you get a stack trace from an exception in a String.
Horrible JDBC Code and What's Wrong With It
Ah, Efficiency: Thou art a goddess who deserves worship, adulation, sacrifice, but thou art also a goddess who gets said worship, adulation, and sacrifice in all the wrong ways. Here's some JDBC code validating a login, trying to be good code (I think!)... that gets it wrong in almost every way possible.
Are JDBC statements portable across databases?
Ah, JDBC. Sometimes, people want to write JDBC code, because SQL is friendly and safe; then they discover that they actually don't want to deploy on MySQL after all, and they run into problems. The question is usually formed in this way: "If I write my SQL in a prepared statement, is it going to work the same way in $OTHER_DATABASE?"
Filtering characters from a Reader
It's an occasionally legitimate question: "How do I filter content from a Reader?" There're related questions for Streams, too. Here's an example of a simple Reader class that shows how to remove specific characters from a Reader.
How can I create a maintenance window for my web app?
Every so often, web applications need maintenance. Yes, even web applications. It's okay - no need to reach for your security blanket. The problem that's come up is: What's a good way to redirect requests during a maintenance window to an error page? As usual, there are multiple answers.
How can I automatically expire data from a database?
Another fairly common question: how can I expire data from a database? This is a case of applying lipstick to a pig: there are ways, to be sure, but the real problem is that you're using a database - a permanent datastore - to handle data that's short-lived.
My data structures have changed - how can I migrate my data model?
Sometimes, people design data structures, persisted entities, only to find that - gasp! - their data structures are more fluid than they expected. When all of your data is transient - meaning that it can be destroyed safely - that's no big deal, because you just drop the tables in question (or the whole database) and start over. (Sound familiar, Rails fans?) Sometimes, that's not enough - so what do you do?
How do I send mail with Java?
You send mail in Java with one of two APIs, basically: JavaMail and Commons-Email. People who use JavaMail fit in one of three categories: they don't know about Commons-Email, they are doing bulk mail and know what they're doing, or they're gluttons for punishment. Here's a class that shows how to send mail with both JavaMail and Commons-Email, for the case of sending to a single address.