My project has a complicated maven structure, with lots of sub projects, and 66 pom.xml files. But for my current task, I'm only modifying one resource file, a .xsl file that I need to test lots of small changes. The build takes 9 minutes, and it spends most of its time recompiling my java source files that haven't changed. Is there any way to use maven to package and build my .war file without recompiling my java source code?
This is a tricky one. Maven is not good at building incrementally.
My first shot would be to try #gaborsch suggestion. But be careful. The results can be inconsistent, depending on your changes. You need to make some experiments to figure out if this works for you.
The second shot would be to speed up the build. You can try to build in parallel, or you can only partly build your multi-module project if only parts are affected (and you are building Snapshot versions).
Gradle is much better at building incrementally (I am a Maven guy, but I have to admit it). But switching to Gradle is probably not the right way to go.
I will suggest what I answer to a similar question.
mvn package -pl my-child-module
This command will build the project my-child-module only.
It won't skip the compilation but at least will skip unwanted modules to be built.
-pl, --projects Build specified reactor projects instead of all projects
-am, --also-make If project list is specified, also build projects required by the list
-amd, --also-make-dependents If project list is specified, also build projects that depend on projects on the list
Related
I am new to using github and have been trying to figure out this question by looking at other people's repositories, but I cannot figure it out. When people fork/clone repositories in github to their local computers to develop on the project, is it expected that the cloned project is complete (ie. it has all of the files that it needs to run properly). For example, if I were to use a third-party library in the form of a .jar file, should I include that .jar file in the repository so that my code is ready to run when someone clones it, or is it better to just make a note that you are using such-and-such third-party libraries and the user will need to download those libraries elsewhere before they begin work. I am just trying to figure at the best practices for my code commits.
Thanks!
Basically it is as Chris said.
You should use a build system that has a package manager. This way you specify which dependencies you need and it downloads them automatically. Personally I have worked with maven and ant. So, here is my experience:
Apache Maven:
First word about maven, it is not a package manager. It is a build system. It just includes a package manager, because for java folks downloading the dependencies is part of the build process.
Maven comes with a nice set of defaults. This means you just use the archtype plugin to create a project ("mvn archetype:create" on the cli). Think of an archetype as a template for your project. You can choose what ever archetype suits your needs best. In case you use some framework, there is probably an archetype for it. Otherwise the simple-project archetype will be your choice. Afterwards your code goes to src/main/java, your test cases go to src/test/java and "mvn install" will build everything. Dependencies can be added to the pom in maven's dependency format. http://search.maven.org/ is the place to look for dependencies. If you find it there, you can simply copy the xml snippet to your pom.xml (which has been created by maven's archetype system for you).
In my experience, maven is the fastest way to get a project with dependencies and test execution set up. Also I never experienced that a maven build which worked on my machine failed somewhere else (except for computers which had year-old java versions). The charm is that maven's default lifecycle (or build cycle) covers all your needs. Also there are a lot of plugins for almost everything. However, you have a big problem if you want to do something that is not covered by maven's lifecycle. However, I only ever encountered that in mixed-language projects. As soon as you need anything but java, you're screwed.
Apache Ivy:
I've only ever used it together with Apache Ant. However, Ivy is a package manager, ant provides a build system. Ivy is integrated into ant as a plugin. While maven usually works out of the box, Ant requires you to write your build file manually. This allows for greater flexibility than maven, but comes with the prize of yet another file to write and maintain. Basically Ant files are as complicated as any source code, which means you should comment and document them. Otherwise you will not be able to maintain your build process later on.
Ivy itself is as easy as maven's dependency system. You have an xml file which defines your dependencies. As for maven, you can find the appropriate xml snippets on maven central http://search.maven.org/.
As a summary, I recommend Maven in case you have a simple Java Project. Ant is for cases where you need to do something special in your build.
Should the Maven clean goal be applied to every build as a best practice to avoid stale CLASS files? Or perhaps always using clean is unnecessary since Maven is smart enough to know which source code needs to be re-compiled based on changes?
compile
install
etc?
Gareth Davis pointed out the potential danger of forgetting to running a clean after re-naming a CLASS file - https://stackoverflow.com/a/4662536/409976.
Example:
Compile module (not whole project) - Foo.java -> target/Foo.class
Re-name to Bar.java & re-compile module -> target/{Foo.class, Bar.class}
re-compile main
BOOM – other module code should’ve failed to compile since it relied on making a Foo class (but it still longer exists since we didn’t clean).
I'm looking into whether the absence of clean will improve build performance on a guest VM within a shared directory. However, I'm not aware of all of the consequences of not always calling the clean step first.
Running clean before any build is always a good practice since the stale class scenario that you have mentioned is completely possible and if encountered, it can create problems in your final artifact.
I'm looking into whether the absence of clean will improve build performance on a guest VM.
By performance, my best guess is that you mean time efficiency. By avoiding the clean goal, you CAN save time since maven will only build the classes where any change was done and it will leave out the rest of the untouched class. So, technically speaking, yes you will save some time in the build process.
However, I'm not aware of all of the consequences of not always calling the clean step first.
Class staleness is by far the most common issue that you may and will encounter.
By experience I can share a couple of things. If you are using an IDE and your project structure is a bit large complex ( A couple of dependant modules etc etc ) then running mvn clean does sometimes confuse the IDE in managing the build path of the project and you may run into ClassNotFoundExceptions. Although not a big issue but you have to do a project --> maven --> Update project to set the build path right.
(Edit However, if you are running it via command lien, then this issue will never arise)
On your dev machines, its all good with mvn install, but when you are deploying a build on production or test server, its best to go with mvn clean before doing a mvn install to make sure no issues arise and all the classes are built once before wrapping them in a jar/war or anything
I'm new to Maven, using the m2e plugin for Eclipse. I'm still wrapping my head around Maven, but it seems like whenever I need to import a new library, like java.util.List, now I have to manually go through the hassle of finding the right repository for the jar and adding it to the dependencies in the POM. This seems like a major hassle, especially since some jars can't be found in public repositories, so they have to be uploaded into the local repository.
Am I missing something about Maven in Eclipse? Is there a way to automatically update the POM when Eclipse automatically imports a new library?
I'm trying to understand how using Maven saves time/effort...
You picked a bad example. Portions of the actual Java Library that come with the Java Standard Runtime are there regardless of Maven configuration.
With that in mind, if you wanted to add something external, say Log4j, then you would need to add a project dependency on Log4j. Maven would then take the dependency information and create a "signature" to search for, first in the local cache, and then in the external repositories.
Such a signature might look like
groupId:artifactId:version
or perhaps
groupId:artifactId:version:classifier
This identifies a maven "module" which will then be downloaded and configured into your system. Once in place it adds all of the classes within the module to your configured project.
Maven principally saves time in downloading and organizing JAR files in your build. By defining a "standard" project layout and a "standard" build order, Maven eliminates a lot of the guesswork in the "why isn't my project building" sweepstakes. Also, you can use neat commands like "mvn dependency:tree" to print out a list of all the JARs your project depends on, recursively.
Warning note: If you are using the M2E plugin and Eclipse, you may also run into problems with the plugin itself. The 1.0 version (hosted at eclipse.org) was much less friendly than the previous 0.12 version (hosted at Sonatype). You can get around this to some extent by downloading and installing the "standalone" version of Maven from apache (maven.apache.org) and running Maven from the command line. This is actually much more stable than trying to run Maven inside Eclipse (in my personal experience) and may save you some pain as you try to learn about Maven.
I am converting a large Java project to use maven. I have a LOT of inter dependencies to work out, but I would like to get it off the ground with maven before I do the real cleanup work. I have broken it up into a few modules plus one giant module; let's call that module monolith.
Monolith has regular Java classes and some gwt classes (with interdependencies). I separated the two parts to have a directory structure like this:
./src/main/java/...
./src/client/gwt/...
So, I can easily get this to compile in eclipse with m2eclipse, but then I can't seem to find how to get it to compile with maven. I saw that the pom file has a build section where you can specify an alternate source and target, but I think it is not a repeatable attribute in the pom:
<build>
<sourceDirectory>${basedir}/src/main/java</sourceDirectory>
</build>
In eclipse, I can adjust the project's .classpath file (in the project properties) to add additional source files (and output dirs) to accomplish what I am looking to do.
Is there any way to do this, or do I need to work out the dependencies first, and separate into separate modules?
If you go against the grain with maven it will be an uphill battle all the way.
Maven doesn't lean towards multiple main source directories, they would do better in maven environment as separate modules.
I've looked at a number of maven gwt projects and archetypes, and none of them seem to take the approach you've suggested.
Have a look at the source structure used by Hupa, also see the archetypes from the Ham and Eggs blog
http://hamandeggs.wordpress.com/2010/01/26/how-to-gae-eclipse-maven/
http://hamandeggs.wordpress.com/2010/07/25/gae-eclipse-maven-update-for-helios/
These also cater for App Engine.
If you really need to separate your java server source from your gwt client source, then monolith needs to be split into more modules.
It is quite common to see gwt projects with a package structure as follows:
com.company.project
.client
.server
.shared
And then specify the source paths in your gwt.xml to include client and shared
What you have is called a maven multi-module project. Take a look at this tutorial on the maven book.
So, I can easily get this to compile
in eclipse with m2eclipse, but then I
can't seem to find how to get it to
compile with maven.
-- I am not sure what you meant by this. M2Eclipse plugin is using maven to build your modules. Perhaps you can clarify this section. Hope the tutorial link helps you.
try to follow this tutorial http://maven.apache.org/plugins/maven-eclipse-plugin/reactor.html
main idea- start from creation of empty project from maven mvn archetype:create and then put you sources to created by maven structure...
also i can strongly recommend to check your dependency tree and effective pom with eclipse plugin tool when you perform this task (for avoid duplicate in dep. & other bad things)
In Java if you package the source code (.java) files into the jar along with classes (.class) most IDE's like eclipse will show the javadoc comments for code completion.
IIRC there are few open-source projects that do this like JMock.
Lets say I have cleanly separated my API code from implementation code so that I have something like myproject-api.jar and myproject-impl.jar is there any reason why I should not put the source code in my myproject-api.jar ?
Because of Performance? Size?
Why don't other projects do this?
EDIT: Other than the Maven download problem will it hurt anything to put my sources into the classes jar to support as many developers as possible (maven or not)?
Generally because of distribution reason:
if you keep separate binaries and sources, you can download only what you need.
For instance:
myproject-api.jar and myproject-impl.jar
myproject-api-src.jar and myproject-impl-src.jar
myproject-api-docs.zip and myproject-impl-docs.zip
Now, m2eclipse - Maven for Eclipse can download sources automatically as well
mvn eclipse:eclipse -DdownloadSources=true -DdownloadJavadocs=true
Now, it can also generate the right pom to prevent distribution of the source or javadoc jar when anyone declare a dependency on your jar.
The OP comments:
also can't imagine download size being an issue (i mean it is 2010 a couple 100k should not be a problem).
Well actually it (i.e. "the size) is a problem.
Maven suffers already from the "downloading half the internet on first build" syndrome.
If that downloads also sources and/or javadocs, that begins to be really tiresome.
Plus, the "distribution" aspect includes the deployment: in a webapp server, there is no real advantage to deploy a jar with sources in it.
Finally, if you really need to associate sources with binaries, this SO question on Maven could help.
Using maven, attach the sources automatically like this:
http://maven.apache.org/plugins/maven-source-plugin/usage.html
and the javadocs like this:
http://maven.apache.org/plugins/maven-javadoc-plugin/jar-mojo.html
That way they will automatically be picked up by
mvn eclipse:eclipse -DdownloadSources=true -DdownloadJavadocs=true
or by m2eclipse