What's with all the Java Build tools?

Question

what's the point of using ant, maven, and buildr? won't the using build in eclipse or netbeans work fine? i'm just curious as to what makes the build tools so special

Answer 1

Different features. For example Maven can scan your dependencies and go download them, and their dependencies so you don't have to. For even a medium sized project there may be a very large number of dependencies. I don't think Eclipse can do that.

Answer 2

• Dependency Management: The build tools follow a component model that provides hints on where to look for dependencies. In Eclipse / Netbeans, you have to depend on a JAR and you don't really know if this JAR has been updated or not. With these build tools, they 'know' updates in dependencies (generally because of a good integration with your source control repository), recalculate transitive dependencies and ensure that everything is always built with the latest versions.

• Access Control: Java, apart from class level access control, has no higher abstraction. With these build tools you can specify exactly which projects you want to depend on you and control visibility and access at a higher level of granularity.

• Custom Control: The Eclipse / Netbeans build always builds JAR files. With custom build mechanisms, you could build your own custom (company-internal) archive with extra metadata information, if you so wish.

• Plugins: There are a variety of plugins that come with build tools which can do various things during build. From something basic like generating Javadocs to something more non-trivial like running tests and getting code coverage, static analysis, generation of reports, etc.

• Transport: Some build systems also manage transport of archives - from a development system to a deployment or production system. So, you can configure transport routes, schedules and such.

Take a look at some continuous integration servers like CruiseControl or Hudson. Also, the features page of Maven provides some insight into what you want to know.

Answer 3

@anonymous,

• Why do you I assume that me, a member of your team, is using an IDE all the time? I might want to build the code on a headless build server, is that ok?
• Would you also deny me the right of using a continuous integration engine?
• May I fetch dependencies from a central repository please? How can I do that?
• Would you tie me to a specific IDE? I can't run Eclipse easily on my very old laptop, but I'll buy a new one.

Maybe I should also uninstall subversion and use patches or just zip folders on a sftp/ftp/Samba share.

Answer 4

The problem with building from the IDE, is that there are tons of settings affecting the build. When you use a build tool all the settings a condensed in a more or less readable form into a small set of scripts or configuration files. This allows in the ideal case anybody to execute a build with hardly any manual setup.

Without the build tool it might become next to impossible to even compile your code in let's say a year, because you'll have to reverse engineer all the settings

Answer 5

On top of all the other answers. The primary reason I keep my projects buildable without being forced to use NetBeans or Eclipse is that it makes it so much easier to setup automated (and continuous) builds.

It would be rather complicated (in comparison) to set up a server that somehow starts eclipse, updates the source from the repository, build it all, sends a mail with the result and copies the output to somewhere on a disk where the last 50 builds are stored.

Answer 6

To expand on Jens Schauder's answer, a lot of those build options end up in some sort of .project file. One of the evils of Eclipse is that they store absolute path names in all of it's project files, so you can't copy a project file from one machine to another, which might have its workspace in a different directory.

The strongest reason for me, is automated builds.

Answer 7

IDEs just work on a higher abstraction layer.

NetBeans nativly uses Ant as its underlying build tool and recently can directly open maven projects in NetBeans. Hence, your typical NetBeans project can be compiled with ant and your maven project already is a NetBeans project.

As with every GUI vs CLI discussion, IDEs seem easier for beginners but once you get the idea it becomes cumbersome to do complex things.

Changing the configuration with an IDE means clicking somewhere which is easy for basic things but for complex stuff you need to find the right place to click. Furthermore IDEs seem to hide the importent information. Clicking a button to add a library is easy but you may still not know where the library is, etc.

In contrast, using a CLI isn't easy to start with but becomes quickly easy. It allows to do complex things more easily.

Using Ant or Maven means that every one can choose his/her own IDE to work one the code. Telling someone to install IDE X to compile it is much more overhead than telling "run <build command> in your shell". And of course your can't explain the former to an external tool.

To sum up, the IDE uses a build tool itself. In case of NetBeans Ant (or Maven) is used so you can get all the advantages and disadvantages of those. Eclipse uses its own thing (as far as I know) but also can integrate ant scripts.

As for the build tools themselves Maven is significantly different from Ant. It can download specified dependencies up to the point of downloading a web server to run your project.

Answer 8

The build tools allow you to do a build automatically, without human invention, which is essential if you have a code base being able to build many applications (like we do).

We want to be certain that each and everyone of our applications can build correctly after any code base changes. The best way to check that is to let a computer do it automatically using a Continouos integration tool. We just check in code, and the CI server picks up there is a change and rebuilds all modules influenced by that change. If anything breaks the responsible person is mailed directly.

It is extremely handy being able to automate things.

Answer 9

If you are a single developer or a very small group, it can seem that a build system is just an overhead. As the number of developers increases though it quickly becomes difficult to track all changes and ensure developers are keeping in sync. A build system reduces the rate of increase of those overheads as your team grows. Consider the issues of building all the code in Eclipse once you have 100+ developers working on the project.

One compelling reason to have a separate build system is to ensure that what has been delivered to your customers is compiled from a specific version of the code checked into your SCM. This eliminates a whole class of "works on my box" issues and in my opinion this benefit is worth the effort on its own in reduced support time. Isolated builds (say on a CI server) also highlight issues in development, e.g. where partial or breaking changes have been committed, so you have a chance to catch issues early.

A build in an IDE builds whatever happens to be on the box, whereas a standalone build system will produce a reproducible build directly from the SCM. Of course this could be done within an IDE, but AFAIK only by invoking something like Ant or Maven to handle all the build steps.

Then of course there are also the direct benefits of build systems. A modular build system reduces copy-paste issues and handles dependency resolution and other build related issues. This should allow developers to focus on delivering code. Of course every new tool introduces its own issues and the learning curve involved can make it seem that a build system is a needless overhead (just Google I hate Maven to get some idea).