So, I’ve used Maven for a few years and about a month ago decided to plunge into Gradle. If I had to do it again my verdict at this point is: don’t bother.

Wish it were otherwise.

As of today, AFAICT, there's no reason to switch from maven and there are plenty of reasons not to. (Caveats: if you're doing Android dev and/or if you want to write custom build logic in Groovy, then go gradle.) I wanted to like gradle more. The simplified format of its build files are appealing. But, after a month, I find I'm mostly just wrestling with it whereas maven, though crufty in many ways, just does the reasonable thing.

Particular points:

+ Maven profiles are useful. While writing the conditional logic for gradle ain't hard, you end up with this logic sprinkled in all sorts of sections of the build file. Yuck.
+ Integration tests - maven knows how to do this out of the box. Gradle... well, it's complicated. You usually have to restructure your code.
+ Parent pom and externalized definitions. Maven... baked in. Gradle... roll your own. Oh, and, those shared, common version numbers... good luck in gradle if you're using that for a plugin because plugin specifier MUST come first therefore you must hard-code those things. Why?
+ Gradle's uber funky way of storing dependencies in its local folder. Why?
+ Building a shaded “uber jar” in gradle is extra work.

There more issues, but perhaps you get the point.

In short, gradle looks better in the showroom or garage, but once you take it out for a spin it doesn’t handle or drive any better for regular tasks and for many it’s worse.

I want an experience that matches the impression given by those initially skinny build files: a place where things just work and most things you do as a java dev are thought of beforehand. Gradle gets props for being more general-purpose than maven. But.... not worth the effort on its own at this point.

I'd rather a tool that just moved maven forward. Maven is a good conceptualization of java development. It would benefit from a serious evolution. Not sure the gradle revolution takes me to a better place, however. Wished it did.

I won’t even cover ant. Haven’t used it in 3+ years except under duress and SOooo often have encountered unmaintainable builds that use ant and have been an operational nightmare. (That said, if you must go that route at least use Ivy with it.)

Maven is older than Gradle. It got a head start. It also had a lot of good ideas (and some bad ones), so it caught on quickly. Gradle is much better IMO, but it’s coming to the party later and many people and projects are already invested in Maven and it works for them.

That’s the answer. Below is just my usual anti-Maven rant.. feel free to skip it if you don’t want to know why you shouldn’t be using Maven. 😀

I won’t use Maven anymore. I’ve had enough bad experiences with it and Gradle helped me deal with them. These days if I have to do any significant work on a project I have control over, if it uses Maven it gets converted to Gradle as a first step.

Just yesterday it happened again. A colleague needed help with a Maven build. Maven is failing and we don’t know why. This has happened a couple times in the last few days. The first time it was a Maven bug that has been around for quite a while. I had to get the Maven source code to debug it and find a workaround. (I filed a bug with Maven as well). This time I will likely have to do the same thing… dig deep into the code of Maven plugins because they don’t produce useful error messages. The error we get is basically “Something is wrong with X” .. and yet we look at X and it is following the documented examples for that Maven plugin exactly. Even that error we have to coax out of it with special commands, as it appears the plugin isn’t even running when it is supposed to normally. With no feedback from Maven as to why it is skipped. Maven builds produce a torrent of useless logging, and usually very little or nothing that will help you diagnose a problem. The most common error message from Maven goes like this, ”something went wrong - I’m not going to repeat it here because that would make things easy, go see if you can find it in the 300 pages of output above, where it won’t be highlighted in red like this is.”

Because Google, or rather, Jetbrains, didn’t bother creating something good for the build process. Gradle is one of the worst pieces of software I have ever seen. Why they’re using it, goes beyond me.
It’s flaky, unreliable, unpredictable, it breaks left and right, and it even spontaneously breaks without even touching it and with automatic updates off.
Someone has to shake up Google and Jetbrains and tell them that enough is enough. Do not bother to even try to fix it. Toss in the garbage where it belong, and create something smarter. Jetbrains is more than capable of doing so. They created all those IDEs and Kotlin for crying out loud. I mean, what is WRONG with them all. I absolutely detest Gradle beyond comprehension.

Ant

Most have been said already. If you are stuck on Ant then you haven’t moved much since 1997. If you are on Ant then move to either Gradle or Maven.

Gradle vs Maven

I have another take on this than most other respondents. Gradle may be newer and offer more flexibility. However that flexibility comes at a cost of possibly creating something “non-standard” when a standard (read: convention-based) solution was indeed available. This is both good and bad.

At the end of the day Gradle doesn’t offer enough of an advantage over Maven … and the thing is: Since there’s so much stuff out there which already uses Maven it will be pretty difficult for you to claim that you are a Java programmer and then not know Maven. The question then becomes: If you want to use Gradle, do you have the bandwidth to really understand both Maven or Gradle. Because you’ll be forced to understand and use Maven anyway.

I’ve seen Gradle being introduced into organizations that were already Maven-based. So now some projects use Gradle and others use Maven forcing developers to learn both. Sure, there are some nice tricks and clarity in Gradle, but not enough. As Java developers we have tons of things we need to learn every day, every week. Having spent time on learning Gradle myself, I’m not sure I would say in hindsight that it was worth it … time wise. I could have spent my time more wisely.

Just my two cents.

I learned in this sequence: Ant > Maven > Gradle

I am currently learning Gradle and using it at work.

IMO, getting slight overview of Ant and Maven before finally deciding to use Gradle is a good way. The advantage: You can better appreciate Gradle for what it is offering.

Ant is a very basic build system which doesn't assume any project structure and the user can orchestrate the build using task dependencies. So, there is potential danger of every software developer coming up with his/her way of defining a folder structure and writing the build script. Another potential danger is that ant build xmls can grow unwieldy.

Maven solves this problem with Ant. In it, Maven assumes a folder structure and it is declarative. Maven is backed up with amazing MVN Repository. You can write your own Maven plugins in addition to the existing plugins. But, Maven's declarative nature works against it at times. You loose the capability to orchestrate the build sequence.

So, Gradle picks best of Ant and Maven.

Similar to Ant, you can define Tasks and define dependencies between tasks. The smart choice Gradle made is to leverage MVN Repository. Hence, most of the Maven plugins are available in Gradle.

Gradle scripts are written in a special purpose build language provided by Gradle (i.e. Domain Specific Language). Domain Specific Language is a language that is finally tailored towards a specific task. This language was not written from scratch but it seats on top of a generic scripting language i.e. Groovy. Groovy has a lot of syntactic sugar and other features that allow us to write the build scripts in language that looks a lot more like a natural like language.

There is a big difference in describing a build and providing explicit instructions on how to actually make the build happen.
The gradle DSL is declarative. So, you are only responsible for describing your build and Gradle itself knows how to make it happen. That means your build scripts are much shorter and much easier to understand. However, within the build you have a full blown programming language at your disposal.

I see Gradle being used by Spring Ecosystem, Android.

To summarize, Gradle is state of the art build system.

If you are starting your own project, and you are limited to using only these three build tools, then you should learn Gradle. It is the most flexible, powerful and easy to use of the three.

If you are working on projects in a team, then you will need to learn whatever is used for those existing projects.

In my opinion, all three tools are difficult to use.

• Ant is low-level scripting in XML, has no opinions about project structure or standard build phases, and become unwieldy at moderate project complexities.
• Maven is also XML based & extremely verbose, but is highly opinionated about what a build should be. If you need to stray outside the norm, you're going to have a very difficult time. As a friend once said "Maven makes the easy difficult and the difficult impossible".
• Gradle is opinionated and terse. So it's quick to get something going and the scripts don't become crazy big when they're complex. But it's based on Groovy, and brings that language's black magic with it. Unless you are prepared to thoroughly understand Groovy and Gradle you may end up with scripts that work (or don't work) without you knowing exactly why - and that's a maintenance problem.

Whenever I see

Not using XML improves readibility.

I can not help myself saying aarrrghhh. I don’t understand why XML is blamed that much regarding readability. Maven XML format is so simple to use and if anyone finds this structure hard to understand, then I wish good luck with DSL. Also this comment:

parent-pom, inherited dependencies, etc it's a nightmare

I can not say Gradle is even a little bit better than Maven when it comes to manage your dependencies. It doesn’t have proper/built-in dependency checking mechanism.

The ones which exist are horrible to read(don’t come with dependencyInsight, it is crap). The given example of jAlarms shows how ugly the syntax of Gradle. When you open the pom file, you can see everything at a glance, but when it comes to Gradle file, you need to spend quite a time to see which dependency is for which configuration, with which version etc.

I really don’t get the idea of using Gradle, if you need to have really really complex build logic, then it might be a choice, but for most of the cases Maven should be the option.

Gradle is more powerful.

Unless it replaces Maven and is managed by the Apache project, I think Maven has a longer shelf life.

So if I want something that’s going to be maintained forever, I’m probably picking Maven, just to avoid the overhead falling into my lap.

Gradle could avoid this by providing a Maven compatibility shim.

It would likely replace Maven in the Apache project, were that to happen, and were Gradle to desire to do that.

Personally, I’d do the shim anyway, and then if people are writing to the Maven API, then they are also writing to the Gradle API.

If they use Grade at that point, all they need to do is use one Gradle-specific API not supported in Maven, and then their code is now addicted, and can never go back to Maven again.

“Embrace and Extend”, baby!

This is easy. Gradle.. every time. Maven works, but it is cumbersome and awkward to use, and becomes just down right horrible when you need to do anything that doesn’t fit what someone has written a plugin for. You get painted into a corner where maintaining a build with Maven becomes a major pain.

I started using Ant for builds, the XML started to get crazy complicated and Gradle made things much easier.

I used Maven for builds and the XML and plugins started to get complicated to configure so I could get the build to do what I needed it to. Gradle made things much easier.

I’ve been using Gradle exclusively now for years, I do not regret it. It isn’t perfect, it can be frustrating to debug some complex build scripts.. there are tons of APIs in Gradle that could do with better documentation or examples, but for the most part it is just so much better than fighting Maven.

You can think of Gradle as goodness of Ant and Maven put together minus the noise of XML. And scriptability with groovy is very big plus.

• Gradle gives you conventions but still gives you power to override them easily.
• Gradle build files are less verbose as they are written in groovy.
• It provides very nice DSL for writing build tasks.
• Has lot of good plugins and vibrant ecosystem

When to use Gradle and When to use Maven ?

Almost everywhere for creating java/groovy project. The build files are much terse.

With Google choosing Gradle as the new build system for Android SDK and mature libraries like Spring, Hibernate, Grails, Groovy etc. already using it to power their builds, there is no doubt that Gradle is becoming de-facto build system for the Java ecosystem.

Gradle is the next evolutionary step in JVM-based build tools. It draws on lessons learned from established tools like Ant and Maven and takes their best ideas to the next level. Following a build-by-convention approach, Gradle allows for declaratively modeling your problem domain using a powerful and expressive Domain-Specific Language (DSL) implemented in Groovy instead of XML. As Gradle is a JVM native, it allows you to write custom logic in the language you are most comfortable with, be it Java or Groovy

Each one does the same thing, so there is really no point. In other words, you would basically have to duplicate all the same setup with each tool. Worse, they have different logic and setups in terms of caching and determining which work needs to be done, etc. So it isn’t like you could compile with one, and then package with the other! I mean, maybe you COULD figure out a way to do that, Gradle is VERY flexible (Maven not so much) but it would be pointless. You should pick one tool and use it, although its perfectly reasonable to use Maven on one project and Gradle on a different project, perhaps due to plugin availability or something like that…

Maven is a project and package manager which creates an initial project structure, installs and upgrades your project packages to current stable versions. Gradle is a package manager and bild tool similar to npm. Ant is a project builder similar to Make. Some developers prefer Gradle over Maven since Maven always upgrades packages to current stable versions which can create dependcy conflicts with projects already sutup with previous package versions.

Maven, Gradle and Ant are primarily used in Java projects. Ant was the first project builder released by Apache Foundation. Most Java libraries and big projects are packed in jar (Java Archive) or war files, an archive file compatible with zip files. These files require a manifest file detail information about the package and the main entry class. Java packages are required to be placed in their own directory or folder, but compiled from their parent folders. In addition, Java requires to include all dependcy class and jar files on a separate environment variable called classpath which complicate project compilation and build. Hence, a project builder and package manager is mandatory for large projects.

Because… Automation

Because build tools let you automate multiple jobs like clicking on several options, zip-unzip etc. If you are developing using an IDE you get the cool UI to do things with one click or hot keys. But when this has been deployed on a linux server, you don’t get that cool UI anymore. And deploying the code from your dev machine and changing the platform properties each time is not a good idea. Build tools let you pack your code into deployable using command line interface. CLI means you get to automate things to do cool stuffs like deploy your code to git and automatically build the deployable on the target machine. Plus advanced built tools let you download libraries directly just be referencing them from several repositositories or jars. Suppose you want the Gson package to be used in your projece. Just mention the repository on github or mention the maven group id on the pom.xml and the build tool will download it from internet. No need to download the jar and add it to your build path. Build tools makes our life easier.

That’s two questions:

#1. Why did they switch? (i.e. why were they unhappy with Ant?)

I think this is well covered in the other answers. It isn’t an interesting question. Mostly any alternative is better than Ant and it is very difficult to find people arguing the opposite these days.

#2. Why did they choose Gradle? (and not for example Maven)

Now, this is the interesting question. I think the answer is a lot more “human” than you may think. I’m not sure it is based on a lot of strictly objective analysis. The simple truth is that if you come from Ant and this has been your world for the past 10 years (as was the case for Android) then Gradle looks more compelling than Maven. Maven is all about convention over configuration. It kind of says to the developer: “If you follow a few rules I’ll make it work for you, nice and simple. On top of this I’ll deliberately (by choice) make it cumbersome for you to step outside of the convention. You can, but we’ll make sure there’s considerable effort involved … and indeed it is meant to be like that”. Ouch!

This sentence in the quotes is what has made Maven successful. But for a person coming from 10 years of Ant he reads this as “surrender yourself to Maven” (as in “give up your freedom” and “customization is impossible”). For an Ant hacker this is completely unacceptable. He thinks of his Ant script as source code. He can express creativity there. (In contrast a Maven person would argue that creativity is the last thing you want in a build system and build scripts are not similar to source code. If you begin thinking of your build configuration as source code there’s something wrong. Creating your build configuration is meant to be dead boring!)

So Maven is clearly not Ant hacker’s first choice. Along comes Gradle and hits that sweet spot for the Ant hacker. Boom! Instant love. In fact if you read Google’s arguments for choosing Gradle, you can see that they are about having a DSL language available within the build and flexibility (as in not being ‘forced’ to do things a certain way, etc). With those requirements, Gradle is a natural choice.

I see Gradle winning over projects who stayed with Ant for a long time and are now looking for something else. Projects who left Ant for Maven seem to stay with Maven.

My two cents: Android project chose Gradle because they came from Ant, not because Gradle is necessarily the world’s best build system. It was mentally a small step for them (Ant → Gradle) compared to moving to an opinionated build system (Ant → Maven).

You’ve got it backwards. Gradle is an improvement over Ant (and Maven). While Gradle is able to run Ant tasks (targets), that’s really best used to transition to Gradle and get away from the more primitive and cumbersome Ant projects. Ant and Gradle are both more flexible than Maven. In that sense they are both superior to Maven for use in the real world. (Maven’s strict and often unrealistic “conform or you’re screwed” philosophy is helpful for beginners, but harmful in the long run.)

Gradle is just a great deal easier to work with than Ant.

There are several good comparisons on the web. Here’s one: Ant vs Maven vs Gradle | Baeldung

It's so much more simple AND powerful than maven. I have a 40+ multiproject build that was relatively easy to setup with Gradle but I have no idea if it would be even possible to do with Maven, at least without having to write some Java classes.

EDIT (details of why it's simpler): Not using XML improves readibility. Using a Groovy-based DSL gives you much more flexibility and power; you can easily define custom tasks, conditionals, etc all in your scripts; a lot of the tasks and properties of the standard build process take closures so you can add your own hooks to the tasks where you need to customize something. Multiproject builds are so much easier to do with Gradle than Maven (ever tried to do one with Maven? parent-pom, inherited dependencies, etc it's a nightmare). You can have fine-grained control if you need it or just tweak a couple of default values and get the results you want.

This is an example of a relatively simple Maven pom:

https://github.com/chochos/jAlarms/blob/master/jalarms-channels/pom.xml

And this is the same build file in Gradle:

https://github.com/chochos/jAlarms/blob/master/jalarms-channels/build.gradle

But don't just take my word for it. Go read Graeme Rocher's blog on why and how they switched Grails from Maven to Gradle; I think Laforge also wrote something about switching Groovy from Maven to Gradle.

In short, it’s a choice.

Gradle was designed to play nice with the standard tool, that one being Maven. Thus using the same file structure and Maven Central as default repository.

But that was to make it easy to migrate from Maven into Gradle. Not to use Gradle along with Maven.

You can do that. But to be able to use both you’ll have to maintain configuration files for both, in sync. That’s gonna cause problems very soon.

Those configuration files are important metainformation, so the project naturally becomes coupled with the tool, unlike IDEs. (*)

Both tools fundamentally do the same thing. There’s no point in the extra cost.

(*) Unless a standard project file structure comes into being. Don’t bet money on it.

Well, both are widely used, Maven is probably the most widely used and esteemed, but Gradle has recently take a great acceptance in the world of computing. First of all, it’s important you know what are the purposes to get for each one, what are the differences between them, and finally, what kind of project is more suitable to be managed with one or another.

Maven is a software project management tool. It is mainly used for Java projects and utilizes concepts from Apache Ant.

The configuration of a project is based on an XML file, which includes the requirements for the build.

It added to Apache Ant the following features:

• repositories management: These are locations that store the jars necessary for the build. There are three repositories: local, central, and remote. The first is located on the machine where the build is performed, and the other two are accessed remotely via http. Maven focuses first on the local repository for a jar search. If it cannot find it, it will search remotely and download it to local to speed up future builds.
• dependencies management: These are declarations of the jars that the project requires for its construction.
• lifecycle management: Part of previously defined goals and phases.
• customization: In order to add a goal it is necessary to develop a Java plugin extending the AbstractMojo class and later add it to the pom.xml file.

So, what about Gradle?

Gradle is an open-source automation tool. It gained rapid popularity since it was essentially designed for multiprojects builds using Apache Maven concepts.

Gradle primarily enhances the following features of Maven:

• language: Gradle does not use the XML language. It is based on DSL since it focuses on solving a specific problem, collaborating on highly structured, efficient, and maintainable builds for multiple projects.
• lifecycle management: It adds the ability to support the entire software life process (including compilation, testing, statistical analysis, and implementation).
• customization: In order to customize a task, just add it to the groovy file (build.gradle)

Main differences are:

• Gradle’s construction time is short and fast, Maven’s performance is slower than Gradle’s
• Gradle’s scripts are much shorter and cleaner, Maven’s scripts are slightly longer than Gradle’s
• Gradle uses domain specific language (DSL), Maven uses XML
• Gradle is based on the task through which the work carried out, in Maven, objectives linked to the project are defined
• Gradle supports Java class incremental compilations, Maven does not support incremental compilations
• Gradle adds support for continuous integration tools, Maven includes support for most continuous integration tools

So far, how can I help you to decide which to choose:

From my point of view, the key is flexibility. If the project can be managed with standard goals or with minimal customization, then Maven is enough. However, if the project requires different behaviors based on multiple construction time variables, then Gradle may respond more effectively.

Hope to be helpful.

Maven does what you describe you want it to do, and in XML form as it was designed so that “what you want to do” with your project are properties of your project, data on what it’s made of. That often makes Maven disturbingly verbose and requiring a lot of concentration to truly know what is that.

Gradle does whatever it feels that probably means when someone puts in their project what you put in your project, with the versions of gradle and all plugins you used. If what you wanted isn’t that, tough luck, what there is to write to get it doesn’t make any sort of sense, and all you can do is copy-paste what others did and claimed it worked for them on the Internet. It is, however, very nonverbose and you can put comment to describe why you added all the lines you added.

Maven was the next generation build tool that was created to address a lot of the problems that tools like Ant had. It instituted a few rules and concepts that helped make projects more organized and uniform:

• By default, projects have a strict structure - java code files go under src/main/java, resource files gounder src/main/resources, and the equivalent test java files and resources go under src/test/java and src/test/resources. This makes it easy to bootstrap a build file because it is clear where the source files are.
• Project code is built into a maven package that has a package group id, artifact id, and version. These packages can be installed in Maven repositories, and this makes it easy to reuse the packages because you only needed the group id, artifact id, and version to pull the appropriate package.
• Maven builds go through a series of phases that are standard for all builds. You can customize what happens in each phase with plugins (and you can even write your own plugins), and some phases may not do anything, but understanding the phases makes it easy to understand what order things happen in.
• Maven introduced the concept of goals to specify what the objective of the build is. Normally the goal is either to compile, test, package, or install, but other goals can be specified as well. These goals can determine how far through the build process Maven will go before stopping. For example, running a mvn compile command will only go as far as compiing the code and not do any testing or packaging.
• Maven added profiles which allows developers to define different build processes as necessary. For example, you might want to build in additional code for testing purposes in lower environments but then leave out that code in production environments.

There were some additional features that really helped developers:

• You can get a dump of the dependency tree, which allows you to see all the Maven packages that will be included in the project. One major problem that developers often run into is conflicting versions of libraries, and looking at the dependency tree can help pinpoint the source of the conflict.
• Maven has the ability to generate build files and even source code based on archetypes. These are templates that include a lot of the boilerplate code that you need to get a project to the state where you can start working on business logic. Leveraging these templates can make projects more uniform and easier to start.
• Maven projects can be nested or inherit from other Maven projects, which makes it so that you can define common dependencies and build configurations in one place and then just add specific dependencies or configurations for individual modules. This makes it easier to add new modules to an existing project or base a new project off an existing project.

I'm less familiar with Gradle, so I can't speak to that, but my understanding is that it builds upon the things that Maven does and takes it further. The point, however, is that build tools like Maven and Gradle have set stricter standards on how code is built so that developers can easily pick up code from any project, know how it is structured, and easily modify it to their needs. These tools also empower developer communities to share libraries. A lot of other languages like Python and NodeJS have similar tools that use standard project structures for the same purpose. If you aren't using one of these tools, there is a good chance you are spending valuable time managing your build process instead of writing code.

Yes. Gradle can be described as the best of Ant and Maven plus more. Converting Ant or Maven projects to Gradle is fairly simple.
With Ant you have to provide all tasks to do what you need whereas Gradle provides convention over configuration meaning that the following is a valid gradle project if you place all files in the conventional locations:

apply plugin: 'war'

By adding
apply plugin: 'jetty'

You can launch you program using gradle jettyRun

Gradle buildscripts are groovy code.
The powerful dependency management allows to builds small changes on a Gradle project that has 400 subprojects and 10000 files in under a minute.

I know that IntelliJ supports Maven well and I assume it supports Gradle reasonably well. I would suggest choosing a build tool first and then choosing an IDE that supports the build tool. You might want to automate your build someday and you’ll need to choose the right build tool for that. Relying on your IDE will become problematic as you begin to automate builds and deployments to servers. Also, the IDE should support standard build tools and not enforce its own opinions. It’s in the nature of build tools to be opinionated though some are more flexible. Finally, the IDE that works well for one developer may not be great for another. Assuming a variety of editors has always worked out well for me. It greatly reduces on-boarding time and allows for more freedom for developers to optimize their workflow where and when necessary. Plus, enterprise IntelliJ costs money if you want to use that.

All 3 are build tools for building java applications.

ANT

1. Ant was initially used by many software developers to build applications.
2. Ant build script should be written in xml and it is called build.xml
3. Ant doesn’t follow any project structure. As a result developers has to write complete build script which sometimes makes a build.xml huge and difficult to maintain
4. Initially Ant doesn’t have dependency management. This leads to the development of Maven. Later on, support had been enabled to integrate with dependency management tools like IVY.

MAVEN

1. Maven uses dependency management to manage the dependencies using repository based approach unlike ANT where developers need to place the dependencies in the class path and refer it in build.xml
2. Maven also uses xml style build script called pom.xml
3. Maven uses pre defined build commands to compile and build the projects unlike ANT where developers has to write a script from scratch.
4. Maven follows standard project structure.

GRADLE

1. Gradle is developed on the concept of both Ant and Maven.
2. Gradle is DSL based script(Domain Specific Language) avoiding xml syntax based language which makes code easier to understand even for the common user.
3. Gradle also uses dependency management and repository based approach to compile and build projects.

As of now Maven occupied the majority of the market share.

Maven and Gradle are build automation tools used for project management. It is very difficult to manage and maintain projects as they grow. In software environment projects deal with many phases and agility makes it more difficult. Following are a few examples where build tools are helpful.

• Build Life Cycle Management : This handles all the sequential steps that are involved to deliver a product. For example, once coding is done then it needs to be compiled, then packaged into some bundle like JAR, WAR or EAR or just before packaging it may require some pre packaging tasks etc. By using life cycle phases(hooks), one can achieve all the above and even more.
• Dependency Management : Almost every small/enterprise level project depends on some third party libraries and one can easily download them and put them into classpath. This looks as simple as download. But this will be nightmare once you dive into JAR hell. Some time it will take more time to resolve jars than developing code. There are possibilities of having transitive dependencies(One jar depends on many more and so on, eg: spring, hibernate, osi etc).
• Contentious Integration : After all software is to automate task then obviously software development it self needs automation tools to deploy our code into respective servers. May be it needs some reports on code quality just before deploying.

Although aforementioned points are must have things for every project, one can do many other automated tasks which save our time and effort. Each of these tools have hundreds of plugins for thousands of tasks we do everyday in our development.