I'm arguing the opposite - if you want stability and time-proven code, you will find the most boring, standard library possible. So, you'd pick Jackson for JSON

I'm arguing the opposite - if you want stability and time-proven code, you will find the most boring, standard library possible. So, you'd pick Jackson for JSON serialization over, say, GSON. But taken further why not just go back to C... Or COBOL? We have to trade off some stability through age for some newer code that's got better potential. Reinventing the wheel should be discouraged only on the basis of it not being tested as well in the fires of production use, not so much for being actually redundant. How many of us would write exactly the same hashing library if we were told to do it repeatedly? So in a scenario like being stuck with Java 6 I'd say you could use libraries like Jodatime and Jodd to make up for certain inconveniences, but it's up to you to decide if your application is fine with the AOP in Jodd v. Guice v. Spring v. whatever J2EE standard is trying to catch up after the fact.