[news.eclipse.tools.jdt] Re: Which Eclipse project files to be placed un

[Eric Rizzo <eclipse-bugs@xxxxxxxxxxxx>]

On 9/17/09 5:00 AM, Michael Ludwig wrote:
> Rich and Eric,
>
> thanks for your thoughts. I found out about Eclipse "User Libraries",
> which seems to be exactly what you referred to, Rich. Very useful. In
> addition to your suggestions, the following article helped me:
>
> InformIT: Configuring an Eclipse Java Project
> http://www.informit.com/articles/article.aspx?p=367962
>
> I'm a bit reluctant to put JARs under version control. Agreed, this
> allows an even faster start-up after checking out the project, but I
> find JARs are not really versioned, so they shouldn't go under version
> control.

User Libraries are indeed a useful feature.

However, I'm perplexed by the statement "JARs are not really versioned." 
Of course they are; most libraries have multiple release and each of 
those has a corresponding JAR, and those different versions/releases are 
not always compatible.
Here's a real-life scenario in which relying on each development machine 
or developer to maintain his own copies of JARs causes problems:
A project is using SomeLibrary (packages as a JAR), version 1.0. Some 
time later, a new developer (or a developer who is setting up a new 
development machine or workspace) goes to get SomeLibrary, but doesn't 
realize that a new version has been released, 1.1. So he sets things up 
to use SomeLibrary 1.1 and begins to work. Two things can go wrong: a) 
the developers of SomeLibrary might not have maintained backwards 
compatibility so that compile errors show up immediately; or b) 
SomeLibrary 1.1 has new functionality or API that was not in 1.0, your 
developer writes new code that uses that, and then the rest of the team 
has build problems as a result (because they all got SomeLibrary 1.0).

In my experience, this happens quite often if the dependencies are not 
managed under version control. VERY often. By versioning the 
dependencies of your project(s), you eliminate these problems that can 
eat up lots of time trying to figure out. There is really no significant 
cost to checking in JARs unless you've got a lot of really large ones, 
and even then they don't change very often so they don't have to be 
downloaded from scm very often.
Maven provides an alternative, but it is a pretty heavyweight option IMO.

Eric