I've been coding Java in Eclipse for awhile without needing to specify dependencies. Now that I learned how Maven does it, I'm wondering: how did Eclipse build projects on its own? How did Eclipse figure out which versions of imports, and which dependencies of dependencies, are needed to make everything work?
Finally, what are the advantages and disadvantages of building a project in Eclipse by starting with New->Other->Maven Project instead of New->Java Project?
To the first question: Eclipse doesn't add any dependency in a standard Java project. You have to manually add to the Build Path all needed JARs, otherwise you'll have compilation errors.
To the second question: if you create a standard Java project Maven is not used, even if you create a pom.xml file in the root of the project. You can always convert a standard Java project in a Maven project (see Convert Existing Eclipse Project to Maven Project).
Your dependencies has always to be in the classpath
When you start a project with Maven, Eclipse will automatically add the Maven repository to the classpath.
When you start a Java project you have to link your library manually in Eclipse and the version of the library is the one you've downloaded.
You can see the difference in your project's Properties > Java Build Path > Libraries
I cloned a GitHub repo onto my disk an successfully built the project by:
ant clean-all resolve create-dot-classpath
within the projects root directory.
I assume this should also be possible from IntelliJ IDE but that fails by doing nothing at all - it simply states "All files are up-to-date" ... what I do is:
"Make module 'pentaho-kettle'"
"Compile module 'pentaho-kettle'"
I could use a hint where to look for a solution or what configuration is most likely missing.
As the project is a multi module project based on Ant and Ivy, you have to
import the project from sources
configure modules (like core, ui, the plugins, …) with the right directories for main and test sources and resources (they seem to overlap with java sources in that project)
setup the class path using an Ivy plugin (I recommend IvyIDEA), use the context menu on the ivy.xml file
and have luck to build. It will be some try and error!
You may also have a try importing from Eclipse as those .project and .classpath files are checked in. But than you also have to check the module directories, the import is more a partial guess and I worry that IntelliJ will not get any information about Ivy from the Eclipse setup.
I work on a big Java application and I'm having problem compiling it under Eclipse Kepler:
the application is based on Maven 3.1.0 and successfully compiles there
I generate Eclipse configuration (project files) using mvn eclipse:eclipse
The problem is that certain classes present in more than one JAR (e.g. imagine a class Http and two versions of this class where newer has more methods) and Eclipse makes a wrong choice of the depending class (older one) for particular project which makes it not compilable.
I tried to move Jars up/down in the project dependencies and it helps in certain situations, however, it means that I'm changing configuration changed by Maven.
Is it possible to configure Eclipse so that is "smarter"? Is it caused by Maven (POM files, a bug in Maven's eclipse plugin, ...) although maven compiles the project without any problems? Any other suggestion?
You should not use mvn eclipse:eclipse. The official way today is to use the m2e plugin (which is much smarter) with File->Import->Existing Maven projects.
When you open a pom.xml file you can see the dependency hierarchy and why a given jar was chosen.
(Note that most but not all standard distributions of the latest Eclipse contains m2e. If your do not you can download it from the marketplace, but it may be easier to download a distribution that has it).
i just started with java, and created a project.
its maven project (i hadn't use maven yet)
so my project have two modules A and B.
and B depends on A, and A depends on some from remote maven repo. and B also depends on some remote repo.
its works fine in Idea IntelliJ and build jars fine.
but afaik .iml files are Idea IntelliJ specific. and pom.xml is maven specific.
and when i inspect files why all depedecy of project is written in .iml files and .idea dir instead of pom.xml(s)
if you want to see the real world source then here it is but its alpha project for learning java deeply.
and when i try to build project on travis-ci.org it unable to resolve dependencies of project
Meghraj,
I have forked your WebTrimmer repo here : https://github.com/ajorpheus/WebTrimmer and fixed a couple of issues which were preventing a successful build:
The travisci fails because you have three jars in the lib folder which are not available to the CI since it's doing a maven build. The fix was to remove those three jars and introduce corresponding maven dependencies as in this commit.
While adding the maven dependencies an exclusion was needed as noted here : The following artifacts could not be resolved: javax.jms:jms:jar:1.1
The WebTrimmerUI depends on the classes in it's sibling module WebTrimmerEngine, therefore a corresponding dependency is needed.
I have converted the project into a pure maven project which is IDE-agnostic. With the above changes, I can build the project from command line and expect that the travisci should be able to as well.
Regarding the question about why the dependencies are duplicated in .iml --- That's not the reason the CI job fails. The dependencies in that file are a snapshot of the dependencies in the pom.xml. This snapshot is updated when the maven project is re-imported manually by the user, or automatically if the maven project is set to 'Auto-Import'.
As Peter Lawrey mentioned in his comment above, if you add a jar to the project, maven does not know about it and it will be present only in the .iml file.
In general, to search and add a maven dependency, the following has always worked for me: https://stackoverflow.com/a/10178586/325742
Hope this helps !
You need to add dependencies to the pom yourself. The .iml files are for storing project specific settings for whatever project you are currently working on.
Having the pom files allows your maven builds to be IDE independent where as the .iml files require you to have IntelliJ.
You can exclude the .iml files from and version control you are using. You can also open an existing maven project directly via IntelliJ by opening its pom.xml and IntelliJ can auto import everything specified in the pom file and will generate new .iml files.
For a project at work, we're considering using the Maven plugin for Eclipse to automate our builds. Right now the procedure is far more complicated than it ought to be, and we're hoping that Maven will simplify things to a one-click build.
My question is, is there a wizard or automatic importer for converting an existing Eclipse Java project to a Maven project, using the Maven plugin?
Or should I create a new Maven project and manually copy over all source files, libs, etc.
Start from m2e 0.13.0 (if not earlier than), you can convert a Java project to Maven project from the context menu. Here is how:
Right click the Java project to pop up the context menu
Select Configure > Convert to Maven Project
Here is the detailed steps with screen shots.
If you just want to create a default POM and enable m2eclipse features: so I'm assuming you do not currently have an alternative automated build setup you're trying to import, and I'm assuming you're talking about the m2eclipse plugin.
The m2eclipse plugin provides a right-click option on a project to add this default pom.xml:
Newer M2E versions
Right click on Project -> submenu Configure -> Convert to Maven Project
Older M2E versions
Right click on Project -> submenu Maven -> Enable Dependency Management.
That'll do the necessary to enable the plugin for that project.
To answer 'is there an automatic importer or wizard?': not that I know of. Using the option above will allow you to enable the m2eclipse plugin for your existing project avoiding the manual copying. You will still need to actually set up the dependencies and other stuff you need to build yourself.
I was having the same issue and wanted to Mavenise entire eclipse workspace containing around 60 Eclipse projects. Doing so manually required a lot of time and alternate options were not that viable. To solve the issue I finally created a project called eclipse-to-maven on github. As eclipse doesn't have all necessary information about the dependencies, it does the following:
Based on <classpathentry/> XML elements in .classpath file, it creates the dependencies on another project, identifies the library jar file and based on its name (for instance jakarta-oro-2.0.8.jar) identifies its version. Currently artifactId and groupId are same as I couldn't find something which could return me the Maven groupId of the dependency based on artifactId. Though this is not a perfect solution it provides a good ground to speed up Mavenisation.
It moves all source folders according to Maven convention (like src/main/java)
As Eclipse projects having names with spaces are difficult to deal on Linux/Unix environment, it renames them as well with names without spaces.
Resultant pom.xml files contain the dependencies and basic pom structure. You have to add required Maven plugins manually.
Right click on the Project name > Configure > Convert to Maven Project > click finish. Here you will add some dependencies to download and add your expected jar file.
This will create an auto-generated pom.xml file. Open that file in xml format in your eclipse editor. After build tag (</build>) add your dependencies which you can copy from maven website and add them there. Now you are good to go. These dependencies will automatically add your required jar files.
Chengdong's answer is correct, you should use Configure>Convert to Maven Project. However, I must add the conversion process has been greatly improved since m2e 0.13.0 : m2e 1.1+ and m2e-wtp 0.16.0+ can now convert the existing eclipse settings into maven plugin configuration .
As for the dependency conversion matter, you can try the JBoss Tools (JBT) 4.0 Maven integration feature, which contains an experimental conversion wizard, plugged into m2e's conversion process : http://docs.jboss.org/tools/whatsnew/maven/maven-news-4.0.0.Beta1.html.
It does not pretend to be the ultimate solution (nothing can), be it should greatly help bootstrap your Maven conversion process.
Also, FYI, here are some ideas to enhance m2e's conversion process, refactoring to use a Maven layout will most probably be implemented in the future.
JBT 4.0 (requires Eclipse JavaEE Juno) can be installed from http://download.jboss.org/jbosstools/updates/stable/juno/ or from the Eclipse Marketplace
It's necessary because, more or less, when we import a project from git, it's not a maven project, so the maven dependencies are not in the build path.
Here's what I have done to turn a general project to a maven project.
general project-->java project
right click the project, properties->project facets, click "java".
This step will turn a general project into java project.
java project --> maven project
right click project, configure-->convert to maven project
At this moment, maven dependencies lib are still not in the build path.
project properties, build path， add library, add maven dependencies lib
And wait a few seconds, when the dependencies are loaded, the project is ready!
There is a command line program to convert any Java project into a SBT/Maven project.
It resolves all jars and tries to figure out the correct version based on SHA checksum, classpath or filename. Then it tries to compile the sources until it finds a working configuration. Custom tasks to execute per dependency configuration can be given too.
UniversalResolver 1.0
Usage: UniversalResolver [options]
-s <srcpath1>,<srcpath2>... | --srcPaths <srcpath1>,<srcpath2>...
required src paths to include
-j <jar1>,<jar2>... | --jars <jar1>,<jar2>...
required jars/jar paths to include
-t /path/To/Dir | --testDirectory /path/To/Dir
required directory where test configurations will be stored
-a <task1>,<task2>... | --sbt-tasks <task1>,<task2>...
SBT Tasks to be executed. i.e. compile
-d /path/To/dependencyFile.json | --dependencyFile /path/To/dependencyFile.json
optional file where the dependency buffer will be stored
-l | --search
load and search dependencies from remote repositories
-g | --generateConfigurations
generate dependency configurations
-c <value> | --findByNameCount <value>
number of dependencies to resolve by class name per jar
https://bitbucket.org/mnyx/universalresolver
My question is, is there a wizard or automatic importer for converting an existing Eclipse Java project to a Maven project, using the Maven plugin?
As far as I know, there is nothing that will automagically convert an Eclipse project into a Maven project (i.e. modify the layout, create a POM, "generate" and feed it with metadata, detect libraries and their versions to add them to the POM, etc). Eclipse just doesn't have enough metadata to make this possible (this is precisely the point of the POM) and/or to produce a decent result.
Or should I create a new Maven project and manually copy over all source files, libs, etc
That would be the best option in my opinion. Create a Maven project, copy/move sources, resources, tests, test resources into their respective directories, declare dependencies, etc.
For converting to Gradle is analogue to Maven:
Right click on Project -> submenu Configure -> Convert to Gradle (STS) Project