Trying to understand what gradle and maven actually do

Question

What exactly do Gradle and Maven "do" that eclipse or sts doesn't? From what I've read it builds, runs, etc which can all be done in eclipse easily.

If I have an existing project I've created, built, and currently runs in eclipse via tomcat, what would I use gradle for?

Answer 1

There's not a lot of benefit to using Maven or Gradle on a small project that you never share with anyone; an IDE can do the build just as well. But as the number of developers increases and the complexity of the build increases, it becomes very useful to separate the build instructions from the IDE. Let's drill into these a little bit.

With the increase in developers, you don't want everyone to have to come by and use your IDE to get a build done. That would be really annoying! So they're on their own machines, but then they tend to have different setups (how dare they have different user account names!) and probably have their IDE installations set up a little differently too. So we need some kind of build instructions that people can use to get things going, and it helps if everyone can use the same build instructions repeatably so that you don't get too many instances of “but it works on my machine!”. It's also very helpful if those instructions are simple enough to use that a new programmer to the team can get up to speed rapidly.

But the other thing that often happens as projects grow in scope is that their builds become more complicated. They very often gain additional dependencies (they didn't start out needing a high-performance date parser and MIME-type identifier, buit they've become required since and you don't want to have to write all those from scratch) and that means you've got to make sure that when the build is done, the right version of those dependencies is used. But that's not the only way that complexity increases. It's also very often the case that you find you're using more automatically-generated code. You might find yourself working with XML schemas or WSDL a lot, or maybe your using Hibernate, or Spring, or … well, there's lots of ways in which things can get complicated, OK? Getting the various steps to do all the build right, reliably, in these sorts of scenarios can be a bit tricky, but encoding them as instructions to something like Maven makes life a lot easier once you've taken the jump in the first place. (It gets even more important when you start trying to deal with projects which need many different sub-programs that work in concert; some of those are plain hard to build even with Maven or Gradle or any other tool.)

And then there's the possibility of offloading work to a build server, running tests automatically, managing dependencies cleanly, etc. IDEs don't handle these all that well by themselves; where they do a reasonable job of it, it's usually because they're using a tool like Maven under the covers to do the heavy lifting.

tl;dr
You don't have to make your code work with a build system, but it helps if you do and in many ways.

Answer 2

Maven and Gradle can do many things that Eclipse doesn't. However, the most important thing they do, is to decouple the bulding and testing processes from the IDE you choose (i.e. Eclipse). When you work on a large environment, with many programmers, usually you can not control the IDE they use. So, it's better to use a tool like Maven and Gradle to standardize these tasks. The same happens with the code examples of a book: instead of the authors having to provide the instructions for configuring any IDE to execute them, they provide the Maven or Gradle files, so the reader can build and test them on any IDE he's using.

Another very important feature that Maven and Gradle give you, is the fact that dependencies are managed without the need of having the executable code under source version control. Instead of having the executable code you depend on as part of the project, you declare the dependencies on a text file (which is under source version control), and then get them from a repository.

However, you may only see the real advantages of using tools like Maven or Gradle (and even Jenkins or Hudson), when you think in large scale projects, developed along many months by teams composed of many developers).