In Maven: The Definitive Guide, I wrote about the differences between Maven and Ant in the introduction the section title is "The Differences Between Ant and Maven". Here's an answer that is a combination of the info in that introduction with some additional notes.
A Simple Comparison
I'm only showing you this to illustrate the idea that, at the most basic level, Maven has built-in conventions. Here's a simple Ant build file:
name="my-project" default="dist" basedir=".">
name="src" location="src/main/java"/>
name="build" location="target/classes"/>
name="dist" location="target"/>
name="init">
dir="${build}"/>
name="compile" depends="init"
description="compile the source " >
srcdir="${src}" destdir="${build}"/>
name="dist" depends="compile"
description="generate the distribution" >
dir="${dist}/lib"/>
jarfile="${dist}/lib/MyProject-${DSTAMP}.jar" basedir="${build}"/>
name="clean"
description="clean up" >
dir="${build}"/>
dir="${dist}"/>
In this simple Ant example, you can see how you have to tell Ant exactly what to do. There is a compile goal which includes the javac task that compiles the source in the src/main/java directory to the target/classes directory. You have to tell Ant exactly where your source is, where you want the resulting bytecode to be stored, and how to package this all into a JAR file. While there are some recent developments that help make Ant less procedural, a developer's experience with Ant is in coding a procedural language written in XML.
Contrast the previous Ant example with a Maven example. In Maven, to create a JAR file from some Java source, all you need to do is create a simple pom.xml, place your source code in ${basedir}/src/main/java and then run mvn install from the command line. The example Maven pom.xml that achieves the same results.
That's all you need in your pom.xml. Running mvn install from the command line will process resources, compile source, execute unit tests, create a JAR, and install the JAR in a local repository for reuse in other projects. Without modification, you can run mvn site and then find an index.html file in target/site that contains links to JavaDoc and a few reports about your source code.
Admittedly, this is the simplest possible example project. A project which only contains source code and which produces a JAR. A project which follows Maven conventions and doesn't require any dependencies or customization. If we wanted to start customizing the behavior, our pom.xml is going to grow in size, and in the largest of projects you can see collections of very complex Maven POMs which contain a great deal of plugin customization and dependency declarations. But, even when your project's POM files become more substantial, they hold an entirely different kind of information from the build file of a similarly sized project using Ant. Maven POMs contain declarations: "This is a JAR project", and "The source code is in src/main/java". Ant build files contain explicit instructions: "This is project", "The source is in src/main/java", "Run javac against this directory", "Put the results in target/classses", "Create a JAR from the ....", etc. Where Ant had to be explicit about the process, there was something "built-in" to Maven that just knew where the source code was and how it should be processed.
High-level Comparison
The differences between Ant and Maven in this example? Ant...
- Ant doesn't have formal conventions like a common project directory structure, you have to tell Ant exactly where to find the source and where to put the output. Informal conventions have emerged over time, but they haven't been codified into the product.
- Ant is procedural, you have to tell Ant exactly what to do and when to do it. You had to tell it to compile, then copy, then compress.
- Ant doesn't have a lifecycle, you had to define goals and goal dependencies. You had to attach a sequence of tasks to each goal manually.
Where Maven...
- Maven has conventions, it already knew where your source code was because you followed the convention. It put the bytecode in target/classes, and it produced a JAR file in target.
- Maven is declarative. All you had to do was create a pom.xml file and put your source in the default directory. Maven took care of the rest.
- Maven has a lifecycle, which you invoked when you executed mvn install. This command told Maven to execute the a series of sequence steps until it reached the lifecycle. As a side-effect of this journey through the lifecycle, Maven executed a number of default plugin goals which did things like compile and create a JAR.
What About Ivy?
Right, so someone like Steve Loughran is going to read that comparison and call foul. He's going to talk about how the answer completely ignores something called Ivy and the fact that Ant can reuse build logic in the more recent releases of Ant. This is true. If you have a bunch of smart people using Ant + antlibs + Ivy, you'll end up with a well designed build that works. Even though, I'm very much convinced that Maven makes sense, I'd happily use Ant + Ivy with a project team that had a very sharp build engineer. That being said, I do think you'll end up missing out on a number of valuable plugins such as the Jetty plugin and that you'll end up doing a whole bunch of work that you didn't need to do over time.
More Important than Maven vs. Ant
- Is that you use a Repository Manager to keep track of software artifacts. I'd suggest downloading Nexus. You can use Nexus to proxy remote repositories and to provide a place for your team to deploy internal artifacts.
- You have appropriate modularization of software components. One big monolithic component rarely scales over time. As you project developers, you'll want to have the concept of modules and sub-modules. Maven lends itself to this approach very well.
- You adopt some conventions for your build. Even if you use Ant, you should strive to adopt some form of convention that is consistent with other projects. When a project uses Maven, it means that anyone familiar with Maven can pick up the build and start running with it without having to fiddle with configuration just to figure out how to get the thing to compile.
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