I need to convert few projects from ant to maven. I know the basics of both, also read a lot of articles on how to. However, is it a good idea to write a pom using eclipse? Or is it better to write it without using eclipse? The M2Eclipse plugin needs maven to be tweaked more, will the changes related to M2Eclipse cause problems when the war is built on jenkins?
Pros of using Eclipse IDE:
The formatting of pom.xml will be taken care, when you add the 'maven-eclipse-codestyle.xml' to the code formatter, as mentioned here. Formatting will be harder when you do it without an IDE.
The auto-completion feature of eclipse will make your coding easier, since it will automatically sense the open tags and close them. You need to close all the open tags manually, if you don`t use an IDE.
You can view the dependency hierarchy of the dependencies added and hence it might be a bit helpful while managing the dependencies.This can be extremely useful ,when you have transitive dependencies (Dependencies within other dependencies). You can find more about transitive dependencies here.
An IDE will warn you of common mistakes that may occur while coding (something like, 'forgetting to close an open tag','placing a tag in an incorrect location'). This will save a whole lot of time. If you don`t use an IDE, you need to correct the mistakes only when you get an exception after executing a maven command.
Eclipse will warn of missing artifacts (when the dependencies are not present in the local repository), which can help you to fix it before executing the maven goal.
Cons of using Eclipse IDE:
m2e plugin will throw 'Plugin execution not covered by lifecycle configuration' errors all over your pom.xml files. These errors won`t affect your build, but may be quite annoying.
I personally have done migration from Ant to Maven2. IMO it is better to write pom.xml on your own so that you wont face any last minute surprises as well as you will get complete overall knowledge on what you are exactly doing with your pom file.
However if you still want to go with m2e, from my experience it did not create any problems at all. Regarding the build - I guess there shouldn't be any issue. You can refer this link if you need more info about m2e and jekins - m2e and jenkins
Related
I had a NoClassDefFoundError problem with some test, launched from IntelliJ. In order to repair the situation, I had to make several changes in many poms of the project - adding new packages and excluding some old ones for to escape the overlapping of them. Also, I reapired the situation with different versions. But the situation did not improve. Again, some package, declared in pom, was not found where it should be.
I refreshed the maven repository by
mvn -e clean install -U
, as is advised in https://stackoverflow.com/a/9697970/715269 - so old and upvoted answer, that it surely looks as Santa.
The problem remained unchanged.
I output the maven map. It was correct and it contained all needed.
I looked at the list of the External Libraries of the project. It was the old uncorrected list of overlapping jars with same names and different versions, and without good packages I added just now, and well seen in maven tree output!
Already hapless,
I reimported packages in IntelliJ
by:
Ctrl+Shift+A, Reimport All Maven Projects.
Ho! The list of libraries got repaired. And the problem, mentioned in subj, disappeared.
The question is: How it could happen, that the same project has that very pom for everything, but gets packages differently being launched in maven and in IntelliJ?
I know about that feature "delegate IDE build to Maven". And I keep it turned off. But I am NOT talking about the different SW for building. Whether they are different or not, they should be up to the actual pom's. And whereas maven, if turned off from the automatic building won't know about changes in poms, IntelliJ KNOWS about them. It could have jars up to pom, or up to maven - it has sense, but it simply has some old rubbish. Was there some deep thought under that construction?
Every time you manually change the pom.xml file, including the dependencies you need to load these changes into IDE. IDE does it on Reload from Maven action. See also Import Maven dependencies.
Intellij doesn't use maven to bulid and run a project except you are delegating build and run action to maven:
Since, IDEA doen't really use maven to run and build, it uses the pom.xml to import the project structure and "tries" to build the project the same way was maven does.
Actually, there are quite a few differences between these to build processes.
Generating sources or filtering resources (don't know if this is still an issue) aren't done during building the project with Intellij IDEA.
In case you are using code generation you have to build the project via maven first and then - when all the resouces are filtered and additional sources are generated - you are able to run, debug aso. the project with Inellij IDEA.
That's an important thing to be aware of and that's the reason why maven and IntelliJ IDEA project structures might get out of sync.
You can enable the "Reload project after changes in build scripts" feature and select the Any changes checkbox to keep your project structure updated:
Why should you disable this feature anyway
If you are working on a build file (gradle or maven is not important) reloading the structure on any change can be very anoying. It's cpu intense, dependcies are fetched aso.
Therefore, I prefer to reload project structure only in case of an external change. This happens when pulling an updated version of the build file for example.
So, I have always used Maven.... thought I would try Gradle.
I went through the instruction to just convert my existing maven setup to gradle, this supposedly sets up the gradle environment from the existing Maven environment.
After conversion, I was able to get simple projects to build with "gradle build".
However, more complicated ones are failing. The problem seems to be the absence of ".jar" files. Maven seems happy with only needing the ".pom" file for dependencies.. yet Gradle seems to require the ".jar" file.
I am not really sure why Maven does not care about the ".jar". Maybe it is lazy and assumes it only needs it during runtime, and as long as it finds the ".pom" it can finish the build. Gradle, then, is not as lazy and requires the actual ".jar".
I don't really know, but am looking for some confirmation on how this works.
Can someone help out?
Thanks!!!!
Maven also needs all the jar files, except for cases where you only need pom information, like parent poms and boms.
If a dependency does not have a jar file, there is probably something missing in your repository.
I'm setting up a (java) maven project that depends on a library (Jettison, among others) that is in the Maven repo. Jettison, in turn, depends on stax. I need to run a tool (Jar Jar Links) on stax (to change the namespace). How do I alter the rules for a transitive dependency in a maven project? My transitive dependencies are being included in my target folder using the copy-dependencies goal (I assume this is how things are usually done). I assume that this is the point where the plugin would be run on the transitively-generated artifact.
Extra question: I don't need this at this point but how would I go about altering the source in the transitive dependency? I can get the jar of the source with mvn dependency:sources but, from there, I'm not sure what the right approach is.
Victory!
Seems at least two people are even more clueless about Maven than me so let me explain what I'm doing before I report the fix at the bottom of this post (spoiler alert: it looks to be a bug in JarJar).
Android uses Java but its missing a lot of the java core (specifically, javax classes). The Android DEX compiler (which converts .jars to Android .dex files) won't even allow you to compile things in the java.* or javax.* namespace because it'll (usually) break stuff. However, in some (many) cases, there are routines that you might want to include -- specifically because they are used by existing libraries. The most legendary is StAX, which is why Google posted an example of how to include it here in the Dalvik repo's wiki. The example uses JarJar... with ant. Transitive dependencies are not really an issue when you aren't using a repo so they are not addressed in the wiki.
I was able to get JarJar to run on my source with Maven but without changing the namespaces in the dependencies (and transitive dependencies), that's worthless. Hence my question.
I thought that the copy-dependencies plugin might be useful for... copying the dependencies and running a transforming plugin in the process. Copying dependencies is mentioned as a step in the official "Maven in 5 minutes" doc so it seemed like a good start but maybe the the people who wrote the official docs don't know how to use it :-) . Either way, it it didn't help -- there is no simple way I could see to transform the jars as it copies.
Using the verbose spew from Maven, I was able to see that Jar Jar was in fact processing my jars properly... and then throwing out the result. It would have packaged the converted classes from the transitive dependencies in my artifact with the rest of my code but, instead, it "Excluded" them. Jar Jar parameters are basically undocumented and most of the tags aren't even listed in the docs but all of the examples I could find use a section with wild-cards that tell it what classes to hold onto. At least I thought (think?) that's what the section is for. Instead, it seems to randomly throw out stuff. Basically, the section is busted. For example, I had:
<keep>
<pattern>com.example.**</pattern>
</keep>
...thinking that this would keep classes that began with com.example. Wrong. It keeps whatever the hell it wants. I tried a million things in that spot until one worked:
<keep>
<pattern>*.**</pattern>
</keep>
This only keeps the classes I wanted -- the classes it updated and the originals of the ones that it didnt touch. Note that ** doesn't even work. This is version 1.8 of the JarJar plugin (the version most poms Ive found use).
Back to work.
I am working on a project and using Maven to build it. The project is a quite big Java web application and it is supposed to work with both Mysql and Oracle databases.
The problem is that there are some specific annotations related to either of the two databases in the source code, plus some other differences, so that I am forced to manually comment/uncomment part of the code before building the application for one of the two databases.
Basically what I would like to achieve is to have my build script, maybe via a Maven profile, to automatically switch the source classes before building depending on the database I want my war to work against.
Putting it simply, the idea is to have MyClass.oracle and MyClass.mysql, and depending on my build profile I should move one of the two in the source dir, rename it MyClass and build. This should be done for some packages, classes, and also configuration files.
Is there any way I can achieve it via "pure" Maven? The only solution I came across till now is to use an antrun plugin and reference an Ant build.xml inside of it.
Thank you,
Mattia
A pure maven solution would be to develop your own maven plugin. Depending on your requirements this can be an overkill, however it is not hard at all, you can see how to achieve this here.
This is a limitation of Maven. One of Maven's purposes is to not have a build script. You should simply use the plugins as available, and setup your project the right way, and magically, everything will build!
There is one solution: Use Ant. Well, not to redo your whole project with Ant, but with the antrun plugin, you can run a few Ant tasks at various phases of your Maven build life cycle.
It's been a long, long time since I've used this, so I am not going to try to write a test pom.xml, but I don't remember it being very difficult to use.
Of course, the correct Maven solution is to divide your project up into "common core" code, and then a separate Oracle and MySql client that uses the "common core". By the way, I hope you're not patching source code. Instead, you're using a properties file to do this for you.
(first, I admit, I have no love for maven/m2eclipse, but it wouldn't be that bad if I could figure out how to overcome these issues)
I am using maven/m2eclipse. m2eclipse is the only good way I know of to suck in the maven jars. Some of these may not have solutions(but I am hoping to be surprised). Maybe solving #9 solves them all?
ISSUES
When I run "mvn clean package", I am dead in the water as far as running a unit test in eclipse while maven is building as I LOVE to multitask but maven prevents me here. How to get around this?
I move eclipse to point to eclipsegen/classes but then the unit tests are still using the classes in target/classes so it's not using my latest code that I just edited in eclipse and debugging is not lining up and it's stepping on blank lines that don't have code.
If I just slightly touch the pom.xml, bam, it builds when I don't really want it to and turning of automatic builds did not seem to help.
On top of #3, I get random pom builds downloading jars which just freezes eclipse from doing anything why the jars are being downloaded(I am a bit multitasker so this frustrates me to no end)
If I want to modify or do something really custom I need, the answer is usually create a java plugin but this then would require me to create another source control project with another automated build making sure the build tags all versions so we can reproduce issues with certain versions. (in ant, I just modify the xml to do custom stuff).
(I hear there is a bug open for 5 years on this one). global exclusions because people on our project keep breaking stuff when they include new things that depend on log4j and sucking that library in breaks us so we want to globally exclude it so people stop breaking the project when adding new things (IVY has global exclusions, why doesn't maven!!!!)
The xml code for generation from an xsd in maven is about 2-3 times the code of doing it in ant. Why is this? That really shouldn't be the case I think.
Running my unit test says xxxx-12.0.8-SNAPSHOT is missing but in my pom.xml it clearly says 12.0.9-SNAPSHOT not .8. ie. m2eclipse gets into some weird state and I get screwed wasting yet more time because someone selected maven
(I don't like IvyDE for the same reasons I don't like m2eclipse). In maven, is there any way like in Ivy to say on a build MOVE ALL jars into target/lib so that I can uninstall m2eclipse(if maven had this one feature, I think all my problems might go away)....That IS AN Ivy feature that rocks by the way!!!!
NOTE: I just realized that uninstalling m2eclipse and running "mvn eclipse:clean eclipse:eclipse" is not really an option since on this project I had to import 30 projects. I think on single projects, that is a great solution.
Is there no way like ant to log the command that was run for debugging purposes? ( in maven how to log the command that was run? )
I should really look into gradle(I hear it's best of maven and ant) as the theory of maven sounded great but you can tell there was a lot of controversy over it(which usually indicates a bad tool). Good tools that really help typically do have some controversy, but not as much as maven has had so it makes me think twice as I don't want to screw the guy who takes over my project(and I know ant will work). Many people I think don't even consider that. They think "I am fine, so why won't the next guy be fine".
Any ideas on how to fix the above issues?
About #9, if you have 2 alternatives :
Execute
mvn dependency:copy-dependencies
See http://maven.apache.org/plugins/maven-dependency-plugin/copy-dependencies-mojo.html for customization options. You'll have to set your Eclipse classpath manually to point to the newly copied jars.
Use JBoss Tools JDT Extensions to get the "Materialize Library" feature (see http://docs.jboss.org/tools/whatsnew/core/core-news-3.3.0.M4.html). You'll basically just have to right-click on the Maven Classpath library, select a destination folder, select (and rename) the jars you want, and you'll get a m2e-free project in Eclipse (still a valid Maven project in command line though).
You can install JBoss Tools JDT Extensions from http://download.jboss.org/jbosstools/updates/development/indigo/
Disclaimer: I like Maven and M2Eclipse, and I have not experienced any of the issues that you mention. In general, M2Eclipse does not get in the way much for the way I'm working.
One thing that might help is disabling the Maven Builder for the projects (right-click the project, select "Properties", then "Builders"). This will get rid of many of the issues you're complaining about.
One other thing that might help you (and comes close to #9 on your list: Uninstall M2Eclipse and use mvn eclipse:eclipse, which will generate Eclipse .project and .classpath files, which include all dependencies as Eclipse project dependencies. Whenever you add or change dependencies, you will have to run mvn eclipse:eclipse again. Give this a try...
Although it does sound like a faster PC would solve some of your issues I do agree that the m2eclipse plugin sucks (although it sucks a little less since eclipse indigo). Because of this I switched to using Intellij for a while but I switched back to eclipse after a month (for me, eclipse is still the best in spite of m2eclipse).
I use m2eclipse to be able to work in eclipse but nothing more. All my maven builds (package, install, whatever) I run with maven itself (command line) simply because there have been too many occasions where the result was different (working in one, not in the other and and maven was always correct).
So, sorry, no direct answers to your questions, just some tips:
1) do it outside eclipse
2) stick to maven standards (target/classes); that will make your life a lot easier
6) using dependency management in a parent pom might help a bit
8) if you get the same issue when running from command line then there is a problem in your pom (resolve using mvn dependency:tree), if not, see 1
9) maybe assembly is an option here but I would not recommend your approach