Is there a guide that outlines how to perform each of the following ant tasks using Maven?
http://ant.apache.org/manual/tasklist.html
Is it considered best practice to use Maven for these tasks or just run them in ANT via ant tasks feature.
There is no mapping between ant tasks and "Maven tasks", because Maven doesn't have tasks. Its philosophy is completely different.
Ant is imperative: you tell Ant what to do with a sequence of parameterized tasks.
Maven is descriptive: you describe which kind of project you have, respect a set of conventions (or describe how you broke these conventions, and Maven decides which tasks it must do.
Somewhere there's a table that shows Maven plugins that are analagous to given Ant tasks, but I can't seem to find it. The "Available Plugins" list might help you out.
There is a list of ant-task-to-maven-plugin at the end of this page -> http://maven.apache.org/plugins/maven-antrun-plugin/usage.html
Unfortunately, it only covers a small subset of ant tasks.
I've recently mavenized ant-based project (I really had it with dependency management) and from that experience I had very little need to retain Ant code. The only place I've used antrun plugin was around custom code generation.
I think that it's perfectly fine to delegate some tasks to ant (and sometimes even to scripts) if that's well documented and saves time and maintenance cost.
One other place where I still use antrun is for echoing some environment properties and generic text to a build output, but maybe it's just my ignorance and there is a Maven way for that.
Related
We are currently attempting to port a very (very) large project built with ant to maven (while also moving to svn). All possibilities are being explored in remodeling the project structure to best fit the maven paradigm.
Now to be more specific, I have come across classifiers and would like to know how I could use them to my advantage, while refraining from "classifier anti-patterns".
Thanks
from: http://maven.apache.org/pom.html
classifier: You may occasionally find a fifth element on the
coordinate, and that is the classifier. We will visit the classifier
later, but for now it suffices to know that those kinds of projects
are displayed as groupId:artifactId:packaging:classifier:version.
and
The classifier allows to distinguish artifacts that were built from
the same POM but differ in their content. It is some optional and
arbitrary string that - if present - is appended to the artifact name
just after the version number. As a motivation for this element,
consider for example a project that offers an artifact targeting JRE
1.5 but at the same time also an artifact that still supports JRE 1.4. The first artifact could be equipped with the classifier jdk15 and the
second one with jdk14 such that clients can choose which one to use.
Another common use case for classifiers is the need to attach
secondary artifacts to the project's main artifact. If you browse the
Maven central repository, you will notice that the classifiers sources
and javadoc are used to deploy the project source code and API docs
along with the packaged class files.
I think the correct question would be How to use or abuse attached artifacts maven? Because basicaly that is why classifiers are introduced - to allow you to publish attached artifacts.
Well, Maven projects often implicitely use attached artifacts, e.g. by using maven-javadoc-plugin or maven-source-plugin. maven-javadoc-plugin publishes attached artifact that contains generated documentation by using a javadoc classifier, and maven-source-plugin publishes sources by using sources classifier.
Now what about explicit usage of attached artifacts? I use attached artifacts to publish harness shell scripts (start.sh and Co). It's also a good idea to publish SQL scripts in the attached artifact with a classifier sql or something like that.
How can you attach an arbitary artifact with your classifier? - this can be done with build-helper-maven-plugin.
... I would like to know how I could use them to my advantage ...
Don't use them. They are optional and arbitrary.
If you are in the middle of porting a project over to maven, keep things simple and only do what is necessary (at first) to get everything working as you'd like. Then, after things are working like you want, you can explore more advanced features of maven to do cool stuff.
This answer is based on your question sounding like a "This features sounds neat, how can I use it even though I don't have a need for it?" kind of question. If you have a need for this feature, please update your question with more information on how you were thinking of utilizing the classifier feature and we will all be more informed to help you.
In contrast to Jesse Web's answer, it is good to learn about classifiers so that you can leverage them and avoid having to refactor code in addition to porting to maven. We went through the same process a year or two ago. Previously we had everything in one code base and built together with ant. In migrating to maven, we also found the need to break out the various components into their own maven projects. Some of these projects were really libraries, but had some web resources (jsp, js, images, etc.). The end result was us creating an attached artifact (as mentioned by #Male) with the web resources, using the classifier "web-resources" and the type "war" (to use as an overlay). This was then, and still does after understanding maven better, the best solution to port an old, coupled, project. We are eventually wanting to separate out these web resources since they don't belong in this library, but at least it can be done as a separate task.
In general, you want to avoid having attached artifacts. This is typically a sign that a separate project should be created to build that artifact. I suggest looking at doing this anytime you are tempted to attach an artifact with a separate classifier.
I use classifiers to define supporting artefacts to the main artefact.
For example I have com.bar|foo-1.0.war and have some associated config called com.bar|foo-1.0-properties.zip
You can use classifers when you have different versions of the same artifact that you want to deploy to your repository.
Here's a use case:
I use them in conjunction with properties in a pom. The pom has default values which can be overriden via the command line. Running without options uses the default property value. If I build a version of the artifact with different property values, I can deploy that to the repo with a classifier.
For example, the command:
mvn -DmyProperty=specialValue package install:install-file -Dfile=target/my-ear.ear -DpomFile=my-ear/pom.xml -Dclassifier=specialVersion
Builds a version of an ear artifact with special properties and deploys the artifact to my repo with a classifier "specialVersion".
So, my repo can have my-ear-1.0.0.ear and my-ear-1.0.0-specialVersion.ear.
I'm currently working an Eclipse plug-in to provide iPOJO manipulation support.
The principle of iPOJO is to modify the .class files generated by the Java compiler to inject some methods and to add/update an entry to the Manifest.mf file.
Currently, my plug-in provides a project Nature and adds a Builder, added at the end of a project builder list, that calls the iPOJO Manipulator.
I use it on PDE projects.
The complete process works but I have a problem :
When my builder has finished its job (and the building process), the whole building process restarts, erasing the output folder and calling my builder again.
If I don't add a safety trick, it makes the building process loop over and over.
As I work on IResource, an IResourceDeltaEvent must be sent at the end of the building process, so I think the best way to avoid that kind of problem is to hide the fact that the resource has changed.
To be clear, I'm looking for a way to modify the class files after a PDE build, without inducing a new build, and without disabling the workspace auto-build property.
Thanks for answers.
I am a little unclear as to what you are describing.
You mention that you want this to work for PDE builds, but PDE builds happen largely outside of the workspace using ant scripts. They do not use IResource, Builder, or IResourceDeltaEvent.
I am guessing that you don't really mean PDE builds, but rather the building of plugin projects inside of the workspace.
In general, Eclipse (JDT in particular) expects that it has complete control over the output folders. However, there is an option in Preferences -> Java -> Building -> Output Folder called "Rebuild class files generated by others". Ensure that this is disabled. Eclipse should not try to rebuild class files that you touch. If your builder only touches class files then it will not trigger other builds after it changes the class files. The only thing is that you need to be careful not to compile things twice (and I think this is the problem that you are describing).
Alternatively, it may be easier for you to implement a CompilationParticipant (and the org.eclipse.jdt.core.compilationParticipant extension point). This will allow you to know exactly when JDT calls a compilation and exactly what it compiles.
Additionally, you will be notified of reconcile operations (ie- changes in working copies that have not been saved). This may be useful for you if you wanted to manipulate files as-you-type.
I'm slowly beginning to understand the importance of module configurations within the Ivy universe. However it is still difficult for me to clearly see how the same chunk of code could have different configurations that have different dependency requirements (the one exception is in the case of test configs that require JUnit on top of the normal dependencies -- I actually understand that 100%!)
For instance, take the following code:
package org.myorg.myprogram.core;
// Import an object from a dependency
import org.someElse.theirJAR.Widget;
public class MyCode
{
public MyCode()
{
if(Widget.SOME_STATIC == 3)
System.out.println("Fizz");
else
System.out.println("Buzz");
}
}
Now aside from the fact that this is terrible code, I just don't see how my program (which, let's pretend is JARred up into MyProgram.jar) could be set to have multiple "configurations"; some of which may require theirJAR and its Widget class, and others that don't. To me, if we fail to provide MyCode with a Widget it will die at runtime, always.
Again, I understand the necessity for test configurations; just not anything else (I have also asked questions about compile- vs run-time dependencies, and I guess I also see the necessity for those as well). But beyond test configs, compile-time configs, and runtime configs, what other module configurations could you possibly need? How would MyCode need a Widget in some cases, and not in other cases, yet still run perfectly fine without a Widget?
I greatly appreciate any help wrapping my brain around this!
Hibernate is a good example. Hibernate supports multiple cache implementations to act as its level-2 cache. You don't want to transitively depend on all the possible caches, only the one you use.
In general, we use the typical compile, test, runtime set of configurations.
To add to SteveD's answer, remember that dependencies can be more than just .jar files. Some dependencies come with source and javadoc files, release notes, license files, etc. Multiple configurations of the dependency might let you select the subset of files you wish to resolve.
You might also want to use configurations to control the contents of different distributions. For example you might want to release the jar on it's own ("master" configuration in Maven parlance) and additionally build a tar package containing all runtime dependencies, with (or without) source code.
Another use for configurations is when you target multiple platforms. I often release groovy scripts packaged to run as standalone jars or as tomcat web applications
I wonder what is the Maven way in my situation.
My application has a bunch of configuration files, let's call them profiles. Each profile configuration file is a *.properties file, that contains keys/values and some comments on these keys/values semantics. The idea is to generate these *.properties to have unified comments in all of them.
My plan is to create a template.properties file that contains something like
#Comments for key1/value1
key1=${key1.value}
#Comments for key2/value2
key2=${key2.value}
and a bunch of files like
#profile_data_1.properties
key1.value=profile_1_key_1_value
key2.value=profile_1_key_2_value
#profile_data_2.properties
key1.value=profile_2_key_1_value
key2.value=profile_2_key_2_value
Then bind to generate-resources phase to create a copy of template.properties per profile_data_, and filter that copy with profile_data_.properties as a filter.
The easiest way is probably to create an ant build file and use antrun plugin. But that is not a Maven way, is it?
Other option is to create a Maven plugin for that tiny task. Somehow, I don't like that idea (plugin deployment is not what I want very much).
Maven does offer filtering of resources that you can combine with Maven profiles (see for example this post) but I'm not sure this will help here. If I understand your needs correctly, you need to loop on a set of input files and to change the name of the output file. And while the first part would be maybe possible using several <execution>, I don't think the second part is doable with the resources plugin.
So if you want to do this in one build, the easiest way would be indeed to use the Maven AntRun plugin and to implement the loop and the processing logic with Ant tasks.
And unless you need to reuse this at several places, I wouldn't encapsulate this logic in a Maven plugin, this would give you much benefits if this is done in a single project, in a unique location.
You can extend the way maven does it's filtering, as maven retrieves it's filtering strategy from the plexus container via dependency injection. So you would have to register a new default strategy. This is heavy stuff and badly documented, but I think it can be done.
Use these URLs as starting point:
http://maven.apache.org/shared/maven-filtering/usage.html
and
http://maven.apache.org/plugins/maven-resources-plugin/
Sean
I developed a Java utility library (similarly to Apache Commons) that I use in various projects.
In addition to fat clients, I also use it for mobile clients (PDA with J9 Foundation profile).
In time the library that started as a single project spread over multiple packages. As a result I end up with a lot of functionality, which is not really needed in all the projects.
Since this library is also used inside some mobile/PDA projects I need a way to collect just the used classes and generate the actual specialized jars.
Currently in the projects that are using this library, I have Ant jar tasks that generate (from the utility project) the specialized jar files (ex: my-util-1.0-pda.jar, my-util-1.0-rcp.jar) using include/exclude jar task features. This is mostly needed due to the size constraints on the generated jar file, for the mobile projects.
Migrating now to Maven I just wonder if there are any best practices to arrive to something similar. I consider the following scenarios:
[1] - additionally to the main jar artifact (my-lib-1.0.jar) also generating inside my-lib project the separate/specialized artifacts using classifiers (ex: my-lib-1.0-pda.jar) using Maven Jar Plugin or Maven Assembly Plugin filtering/includes. I'm not very comfortable with this approach since it pollutes the library with library consumers demands (filters).
[2] - Create additional Maven projects for all the specialized clients/projects, that will "wrap" the "my-lib" and generate the filtered jar artifacts (ex: my-lib-wrapper-pda-1.0 ...etc). As a result, these wrapper projects will include the filtering (to generate the filtered artifact) and will depend just on the "my-lib" project and the client projects will depend on my-lib-wrapper-xxx-1.0 instead of my-lib-1.0. This approach may look problematic since even that will let "my-lib" project intact (with no additional classifiers and artifacts), basically will double the number of projects since for every client project I'll have one lib, just to collect the needed classes from the "my-util" library ("my-pda-app" project will need a "my-lib-wrapper-for-my-pda-app" project/dependency).
[3] - In every client project that uses the library (ex: my-pda-app) add some specialized Maven plugins to trim out (when generating the final artifact/package) the classes that are not required (ex: maven-assembly-plugin, maven-jar-plugin, proguard-maven-plugin).
What is the best practice for solving this kind of problems in the "Maven way"?
The Maven general rule is "one primary artifact per POM" for the sake of modularity and the reasons one shouldn't break this convention (in general) are very well explained in the How to Create Two JARs from One Project (...and why you shouldn’t) blog post. There are however justified exceptions (for example an EJB project producing an EJB JAR and a client EJB JAR with only interfaces). Having said that:
The mentioned blog post (also check Using Maven When You Can't Use the Conventions) explains how you could implement Option 1 using separate profiles or the JAR plugin. If you decide to implement this solution, keep in mind that this should be an exception and that it might make dependency management trickier (and, as you mentioned, pollute the project with "client filtering logic"). Just in case, I would use several JAR plugin executions here.
Option 2 isn't very different from Option 1 IMO (except that it separate things): basically, having N other wrapping/filtering projects is very similar with having N filtering rules in one project. And if filtering makes sense, I prefer Option 1.
I don't like Option 3 at all because I think it shouldn't be the responsibility of a client of a library to "trim out" unwanted things. First, a client project doesn't necessarily have the required knowledge (what to trim) and, second, this might create a big mess with other plugins.
BUT if the fat clients are not using the whole my-lib (like server-side code would require the whole EJB JAR), then filtering isn't the right "maven way" to handle your situation. The right way would be Option 4: put everything common in a project (producing my-lib-core-1.0.jar) and specific parts in specific projects (that will produce my-lib-pda-1.0.jar etc). Clients would then depend on the core artifact and specialized ones.