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I am about to start a Java project just for practice. I've read about Maven, but I don't actually understand when it is meant to be used.
Can you give me some practical tips? Does Maven help a lot? What does Maven actually do for my project?
What it does
Maven is a "build management tool", it is for defining how your .java files get compiled to .class, packaged into .jar (or .war or .ear) files, (pre/post)processed with tools, managing your CLASSPATH, and all others sorts of tasks that are required to build your project. It is similar to Apache Ant or Gradle or Makefiles in C/C++, but it attempts to be completely self-contained in it that you shouldn't need any additional tools or scripts by incorporating other common tasks like downloading & installing necessary libraries etc.
It is also designed around the "build portability" theme, so that you don't get issues as having the same code with the same buildscript working on one computer but not on another one (this is a known issue, we have VMs of Windows 98 machines since we couldn't get some of our Delphi applications compiling anywhere else). Because of this, it is also the best way to work on a project between people who use different IDEs since IDE-generated Ant scripts are hard to import into other IDEs, but all IDEs nowadays understand and support Maven (IntelliJ, Eclipse, and NetBeans). Even if you don't end up liking Maven, it ends up being the point of reference for all other modern builds tools.
Why you should use it
There are three things about Maven that are very nice.
Maven will (after you declare which ones you are using) download all the libraries that you use and the libraries that they use for you automatically. This is very nice, and makes dealing with lots of libraries ridiculously easy. This lets you avoid "dependency hell". It is similar to Apache Ant's Ivy.
It uses "Convention over Configuration" so that by default you don't need to define the tasks you want to do. You don't need to write a "compile", "test", "package", or "clean" step like you would have to do in Ant or a Makefile. Just put the files in the places in which Maven expects them and it should work off of the bat.
Maven also has lots of nice plug-ins that you can install that will handle many routine tasks from generating Java classes from an XSD schema using JAXB to measuring test coverage with Cobertura. Just add them to your pom.xml and they will integrate with everything else you want to do.
The initial learning curve is steep, but (nearly) every professional Java developer uses Maven or wishes they did. You should use Maven on every project although don't be surprised if it takes you a while to get used to it and that sometimes you wish you could just do things manually, since learning something new sometimes hurts. However, once you truly get used to Maven you will find that build management takes almost no time at all.
How to Start
The best place to start is "Maven in 5 Minutes". It will get you start with a project ready for you to code in with all the necessary files and folders set-up (yes, I recommend using the quickstart archetype, at least at first).
After you get started you'll want a better understanding over how the tool is intended to be used. For that "Better Builds with Maven" is the most thorough place to understand the guts of how it works, however, "Maven: The Complete Reference" is more up-to-date. Read the first one for understanding, but then use the second one for reference.
From the Sonatype doc:
The answer to this question depends on your own perspective. The great
majority of Maven users are going to call Maven a “build tool”: a tool
used to build deployable artifacts from source code. Build engineers
and project managers might refer to Maven as something more
comprehensive: a project management tool. What is the difference? A
build tool such as Ant is focused solely on preprocessing,
compilation, packaging, testing, and distribution. A project
management tool such as Maven provides a superset of features found in
a build tool. In addition to providing build capabilities, Maven can
also run reports, generate a web site, and facilitate communication
among members of a working team.
I'd strongly recommend looking at the Sonatype doc and spending some time looking at the available plugins to understand the power of Maven.
Very briefly, it operates at a higher conceptual level than (say) Ant. With Ant, you'd specify the set of files and resources that you want to build, then specify how you want them jarred together, and specify the order that should occur in (clean/compile/jar). With Maven this is all implicit. Maven expects to find your files in particular places, and will work automatically with that. Consequently setting up a project with Maven can be a lot simpler, but you have to play by Maven's rules!
Maven is a build tool. Along with Ant or Gradle are Javas tools for building.
If you are a newbie in Java though just build using your IDE since Maven has a steep learning curve.
Related
My friend and I are working on a Java project collaboratively. We are both very inexperienced with regards to Eclipse and Git alike.
The primary goal is:
For my friend and I to seamlessly contribute to the code via git, with minimal limitation.
To be able to develop the SWT interface without running into dependency errors that might arise due to absolute class paths and/or due to differences in OS (it would be beneficial if I could work on the project not only on my Windows machine at home, but my Macbook as well)
When I looked up the question, it seemed this question had the answer.
However, doesn't changing the build path affect the .classpath, and will thus be affected when you commit changes to git (see goal #2)? How do I ensure that virtually anyone can clone my repository, regardless of OS (see goal #1)? The other answers I have found involve setting the class path variables—however, as I have said, I am woefully inexperienced with Eclipse. I have also heard that Maven might be the answer, but I have no clue how to use the pom file and how to set it up for the 10 or so different jars in the "Referenced Libraries" part of my project.
Thank you in advance for the assistance
We are both very inexperienced with regards to Eclipse and Git alike.
And presumably SWT and Maven as well? Brace yourself for an exercise in patience and frustration - this sounds like a very ambitious (but not impossible) goal without much experience in these things.
develop the SWT interface [...] not only on my Windows machine at home, but my Macbook as well
SWT has different .jars for different OSes and architectures. If you truly want a single .jar that can be run on different platforms, it's not going to be trivial to handle which one is used at runtime. I would recommend building different assemblies depending on the target OS. If that is simply something you cannot do, then unfortunately I can't help much in regards to how to load different SWT .jars at runtime.
Maven might be the answer
Maven will definitely help, and you can use this repository in your pom.xml to get the corresponding SWT dependency: http://maven-eclipse.github.io/maven.
I have no clue how to use the pom file
A bit of Google-searching should bring up some very basic Maven examples. Take some time to understand the different parts of the pom.xml file (Maven in 5 Minutes).
how to set it up for the 10 or so different jars in the "Referenced Libraries"
You will need to find the corresponding Maven dependency for these. Eclipse will be very helpful with this, and you will not need to manually manage the .classpath file (How do I get my Eclipse-Maven project to automatically update its classpath when I change a dependency in my pom.xml file?).
Without throwing too much info at you, while still trying to provide a helpful answer, I would recommend (after getting a grasp on Maven basics) taking a look at using profiles in your pom to determine which SWT dependency will be used (Related: SWT on different systems). This will address your primary concern, as you will no longer be hard-coding a platform-specific dependency, so anyone on a different OS can now build your project.
For my friend and I to seamlessly contribute to the code via git, with minimal limitation.
IMO Git will be the least confusing part about what you're trying to achieve :) That said, just take some time to learn the basics of Git and you should be fine. It's not overly complicated once you understand the basics and stick to the basics.
In general, be aware that with SWT there are some nuances with how it will look/behave on different OSes. Just because something works for you Windows doesn't mean that it will look/behave exactly the same way on a Mac.
Side note: A "gotcha" that you will eventually run into on macOS is the need for the -XstartOnFirstThread JVM argument (Running SWT based, cross-platform jar properly on a Mac).
I have a project that's currently built with ant that pulls the latest trunk version of Solr in through git and then builds through ant. I'm pretty used to Maven and its system for dependencies at this point and find our old ant way of doing things pretty messy and hard to maintain. With that said, basically everywhere I seem to look online, people are building solr with Ant, and the few tutorials I found for doing things with Maven are all along the lines of this one, which doesn't seem to work.
So, to be clear, all I'm looking for here is a clean way to develop the project in Eclipse and to be able to deploy it. I'm sure someone must have done this before and must have a good answer. I'd be really interested in hearing it.
I just got it working by throwing all dependencies into Maven, making my own repo for a pegged version of Solr 4.0-SNAPSHOT, copying the web.xml from it into src/main/webapp/WEB-INF/, and running things through mvn jetty:run with salient variables passed in as arguments as:
mvn jetty:run -Dsolr.dataDir="./solr-data" -Dsolr.master-host="localhost" -Dsolr.solr.home="./solr-home"
This method is officially unsupported, but it means I no longer have to bother with ugly ant configs or holding all of Lucene and Solr in git repos attached to my project, so I could build from them. It also means changing/updating versions just requires a one line change in my pom.xml instead of digging through and switching a whole ton of extraneous configs. I'm pretty happy, and once I got a better feel for how Solr is supposed to work, reconfiguring the project really wasn't that bad.
This answer is probably more a comment, but a comment is too small to expose it all.
I know nothing about Solr, but from a neutral point of view, I would say you have two options:
Mavenize Solr (looks like what is suggested by your article). Maybe you could post another question on what problems you encounter using their solution.
Invoke the original ant tasks using the maven-antrun-plugin. This would also probably require to attach the built jars (or if it only contains classes/resources, jar them first). You could decide to install them locally using maven-install-plugin or attach them with maven-build-helper-plugin.
In eclipse, there are plenty of tricks to access the built files. You could simply add the project as a dependency.
This second option should work, but I don't find it very clean
You should be able to use Maven if you want, I know some of the Solr developers do. Have a look here: http://wiki.apache.org/solr/HowToContribute#Maven. This isn't the most supported way though, and I can't help you with this since I never tried it.
I actually work with Solr + Ant and there's basically a task for everything: ant test, ant dist and so on. I agree that's a bit old fashioned, but it works. Lately the build has been improved a lot introducing Ivy as dependency management tool, in order to remove all jars from the source tree.
Let me know if you have some specific problems with ant, maybe I can help you more.
I'm trying to learn project automation and I'm using the book Pragmatic Project Automation as a guide. It's examples are in Java so I find it easier to follow it along in Java. I don't have any experience using Java or any of its IDEs. However, I've learned some C# using Visual Studio (although I'm still a beginner).
I'm having trouble understanding some parts of setting up a Java project. I'm using Netbeans IDE 7.0 on Windows 7. With Visual Studio, I have a solution with projects underneath. With Netbeans, I appear to just have a project with directories determining the rest of the structure (and the IDE to some degree)? The equivalent to Add Reference appears to be adding a source to the Classpath. There also seems to be a degree of separation between the compiler and the IDE. I'm currently in a situation where I can compile my project just fine while the IDE tells me I still have errors (and I assume this is because I have the project set up incorrectly).
I'm basically looking for analogies that will help me better understand Java project structure.
Lots of similarities between the two languages and IDEs. I spent many years in both. For starters the equivalent to 'add reference' in VS is adding a library or jar in netbeans. In respect to a reference - a jar is pretty much the same thing as a module or .dll in VS. A jar is a compiled reference. To add a reference just go to the project menu and then properties then to the libraries menu from there you can add either pre-assembled netbeans libraries, which are collections of .jar's, or a single .jar, or even a project. Once you add a reference you can import them into your class just like you would in C#.
Netbeans doesn't really have a 'solution' as VS does. You deal with individual projects. It does however have the capability to add a project as a reference so you don't have to continually re-build the references when you change something between multiple projects. It also has project groups to group similar projects.
Lastly Apache ANT is responsible for tying everything together in the background. Netbeans creates a build.xml and build-impl.xml file in the background to tell ANT how to assemble the project into a .jar.
There are my other things to cover but I thing this answers most of your questions. Does this help?
I can't speak for NetBeans, as I use Eclipse, but you are on the right track with classpath being roughly equivalent to references in the Visual Studio world. Libraries (usually .jar files) are placed on the classpath and must be there both at compile time and runtime (you specify the classpath to the compiler at compile time, and to the JVM at runtime). The classpath can contain many different entries, and they can be anywhere in the project structure (or outside of it entirely).
Java itself doesn't impose many restrictions on your project structure, although various IDEs and build tools do. The one thing that is a universal restriction in all Java environments is that source files (and class files) are placed in a directory named after the package name. So if your package name is com.test.something, then your source files will be in SRC_DIR/com/test/something, and your class files in OUT_DIR/com/test/something (note: SRC_DIR and OUT_DIR are not special variables; each IDE will have a different way to specify those directories).
Java libraires tend to heavily build-on one-another, so at some point, you'll find that the classpath entries are too many to manage manually. Before you get there, you'll want to take a look at Apache Maven or Apache Ivy which are dependency management tools. You'll need to understand how they work (either one, not both) and how to integrate them with your IDE. If you use Eclipse and Maven, m2eclipse offers fairly complete integration between the IDE and the dependency management tool.
With Netbeans, I appear to just have a
project with directories determining
the rest of the structure (and the IDE
to some degree)?
Visual Studio dictates a particular project layout and since the compiler is so tightly integrated into the IDE there's no real concept of a build script. In contrast, Java has no such structure (although certain 'best practices' have emerged such as having a 'src' directory for source files, 'lib' for libraries, 'test' for test source, etc.) and a build script is usually required to tell the compiler were to find source files and libraries, what artefacts to produce and a miscellany of other chores (running tests, deployment, creating code metrics and so forth).
In simple cases, the IDE will take care of this for you (if you follow the convention for that particular IDE) but ultimately you will probably want to take a look at a build tool to understand what's going on behind the scenes. Apache Ant and Apache Maven are both prominent offerings. Ant is very flexible whereas Maven attempts to dictate a common layout. I suggest you investigate both and see which suits.
There also seems to be a degree of
separation between the compiler and
the IDE. I'm currently in a situation
where I can compile my project just
fine while the IDE tells me I still
have errors
If your code compiles, it is correct. The IDE is simply acting in an advisory capacity (and will highlight issues beyond compiler errors, such as warning you of potential code mistakes or bad practice).
and I assume this is because I have
the project set up incorrectly
This is a possibility although, as stated above, there are many other explanations.
I'm working with a small team of developers. My job is to convert a Make project (with Intellij Idea 9.0) into a Maven 2 project.
The problem is : we spend a lot of time during the development. With Make, only one complete build was required and then any change did not consume a lot of time (almost instantaneously). On the other hand, with Maven 2, a little change takes a lot of time to run.
Any solution ? Thanks.
The problem you're facing and its description are not clear (what is your project structure, how you build it, how much time does it take to compile one change, etc) but here are some practices that could help:
Use incremental builds (i.e. don't use clean at each build).
Use binary dependencies (i.e. multiple modules with dependencies vs of a huge monolithic module).
Use advanced reactor options for smart reactor build (to build only the required subset of modules).
Use Maven Shell (if you're not aware of this project, CHECK IT OUT).
Personally, I'm not experiencing "lot of time to run" problems with my projects.
On the other hand, with Maven 2, a little change takes a lot of time to run.
I'm not really sure that this has to be true. For a single Maven project, the compile phase doesn't need to recompile all source from scratch, just what has been updated since the last run (assuming you haven't done a clean, etc.).
Without further details though it's hard to offer any advice. Have you converted to Maven and are finding that it seems to be excessively re-building many parts of your projects? If so, please provide more details as Pascal mentions aboves. Or is this just a question driven by fear?
IntelliJ can load the module/project configuration from the pom files. This means that during development, use IntelliJ's build based of the pom files (which is incremental and quick) and only use maven stand alone for continous integration and releases.
I am looking for an lightweight Java build tool. As light as possible. Even at the expense of features. Any recommendations?
As light as possible? That must be javac running from within a batch file or shell script.
But why?
There are only really two choices: Ant or Maven.
Ant is essentially a scripting tool that you can do anything with but you have to write everything yourself.
Maven comes with a lot of predefined project types. It will dictate a directory structure to you (which some people don't like) but will also handle dependencies (which Ant can sorta do with Ivy).
Personally I prefer Maven. A few lines of XML will get you the tasks to run unit tests, stop and start a Web container (eg Jetty or Tomcat), etc.
As said elsewhere, your real choice is between maven or ant. To echo other sentiments, I find there is more configuration to do with ant, so I prefer maven. That said, a lot of people tend to criticise maven in that although you need less configuration, it downloads a lot of dependencies (and dependencies/ dependencies), so it all depends on what you mean by "light" - do you mean light in configuration or light in dependency jar downloads/installation size?
If you want something light in terms of config and downloads, you are better off with a shell script, but that will only be as feature-rich as you have time to make it!
I'd again recommend Maven2 - it is very feature rich through the use of plugins, but it can also be very "light" (depending on what that means):
it doesn't need hard installation (just unzip directory + add the path to it to the environment variables (depending on OS))
it doesn't require configuration - just copy-paste a simple POM file and your build is ready. You will just have to follow the directory structure conventions of maven
it has a plugin for every IDE, so using it with GUI makes it even easier.
Of course, an alternative is ant, but I find it less "light". And I find it less light, because ant scripts grow ugly and unpredictable, and become hard to manage, while maven scripts stay simple, because of the rich functionality provided with the tool.
It really depends on your definition of 'light'. Do you want a tool that requires very little work to use (light on code)? If so, Maven or Gradle might be a good option. Maven has been around for a while. If you are doing something that follows their conventions, then you will need to write very little in your pom.xml files. If you start deviating from the norm it can get difficult to make it do what you need (making things less light). Gradle is also an option. It hasn't be around as long as Maven, but allows you to deviate from the convention easier.
If you are looking for something that is light in terms of the tools itself being lightweight, Apache ant may be a better option. It doesn't have the conventions built in like Maven. If you have a non-standard build that is pretty simple it might be possible to create a very light ant script to do your build.
Maven is simplest if you follow its directory structure. If you are on linux or unix system, I would use shell script. Or you could consider IDEs eclipse or netbeans, they will do the job for you, and dependencies are very easy to configure.
Have you tried BlueJ (http://www.bluej.org/) ?. I used it a few years ago to teach students. It is simple in the sense you can just copy/paste code and run it. It was created to teach students, hence is very simple and good for java starters. Note that it is is a full IDE, not a command line tool like maven or ant.
If you are going to stick with standards, Maven is the best bet.
If you want flexibility consider Groovy AntBuilder. terse syntax, and full power of ant and groovy scripting.