I am trying to convert my existing web app project into maven. I have a bunch of jars in my project manually downloaded and kept in a directory. While converting to maven, I need the name of group id and artifact id of these jars so that I can mention it in pom.xml.
Is there any other way than manually searching for each jar name in mvnrepository.com?
I think you're slightly out of luck. There might be a chance that some of the jars contain the information you're looking for under
META-INF/maven/<groupId>/<artifactId>/pom.properties
But other than that, #JFabianMeier is right, it's manual labor. And please be aware that Maven uses transitive dependencies that may affect your classpath differently than when you specify the jars from a directory.
You might have to add exclusions to your POM's transitive dependencies to get the classpath as you want it.
Related
We are relatively new to Maven and now face a problem.
We have a Maven project (projectA) whose JAR is the dependency of several other projects. Some of the other projects are some custom web container while others are not, so some of projectA's dependency jars are provided in the case of the custom web container, but should be runtime scope in the case of other projects. We currently use exclusion list to filter out the provided jars in the case of the custom web container.
We are wondering if it would be better to use maven profiles. We know how to create the profiles with different dependencies (actually same dependencies different scope), and in both profiles, the built projectA jar is identical bit-wise. But what we don't know is, when we deploy/release the projectA jar artifact to a maven repository, what should the pom.xml look like? For these web container projects, the pom.xml should not include the provided jars, but for other projects, the pom.xml should include these jars.
We can use a different name for the jar in each profile and deploy each with a different pom.xml, but since these jars are identical bit-wise, it doesn't seem like a perfect solution. So we thought there's gotta be a better solution to this problem, only that we don't know since we are relatively new to Maven. Thanks.
The POM is the POM. You seem to be talking about managing transitive dependencies in other projects that reference "A". Your options in Maven are fairly limited:
You can use exclusions to remove transitive dependencies that you don't want.
You can declare dependencies in "A" as "provided", but this is only really correct if that jar actually is provided in A's target environment. It's primarily intended for Java EE api dependencies, like servlet-api, which are provided by containers and prohibited from being included in WAR files.
You can declare dependencies as optional, which is what people usually mean when they say "provided", and manually include those dependencies in the places where they're needed.
I'd personally choose the "optional" route because it's the job of each project to pull in the dependencies it needs, and if something is optional when using "A", it just means things that use "A" have to explicitly choose whether they'll use that optional part of it. This tends to be the best fit when building an artifact that has multiple, differing use cases.
For additional help in this area, you can also use the maven enforcer plugin to ban certain dependencies from builds so that you don't accidentally get jars that you don't want.
Typically, a maven built jar artifact will have it's pom included under META-INF. I recently noticed that the Spring jars don't have this. So, that causes me to wonder about the purpose of that pom.
It seems like maven retrieves the pom directly from the repository when it's doing things that require knowledge of the artifacts meta-data, e.g. when determining dependencies.
So, what's the embedded one for?
The Maven docs suggest two reasons for the pom in this location.
1) Merely for reference, as a convenience. As the docs say, it makes the artifact "self describing"
2) You can get at this information from within your application using Java. This enables the arfiact to auto-report it's version within the application.
http://maven.apache.org/guides/getting-started/index.html
The pom you will find in the repository is not necessarily the one used to build the artifact. It is aimed at the users of the artifact and can be customized when building your artifact.
The one included inside the artifact IS the one used to produce the artifact.
There are options to not have it included in the artifact.
I am writing pom.xml for our project. I need to copy two different versions of same jar. But I searched maven docs and found that Maven has no support for this. Is there any other way to do that?
Note: Both jars have same groupid and artifact id.Only their versions are different.
Thanks in advance!
As you already know, Maven was designed to make sure that you will never have two JARs with the same coordinate (group + artifact id) but different versions on the classpath.
There is no way to achieve what you want without modifying the POMs of the JARs
So you need a workaround. Here are a couple of solutions:
Give the JARs different classifiers. Typical classifiers are "tests" and "sources" but they can be anything.
Move the version number to the artifact id and give the two JARs a new version.
For all approaches, you will need to download the JARs (and probably their POMs as well) and install them again using mvn file:install (after changing the POMs) or deploy them with mvn deploy:file if you run your own Maven proxy.
I have two maven projects, the second project extends some classes of first project. I want to create the jar file with all dependencies of first project and include it to another project as dependency. I am searching this since long time, is it possible to do it?
I am new to maven, any help on this would be highly appreciated.
Thanks
If you just want to add the dependencies to another project you add the second project dependency to your new project and the first one will be inherited and automatically included. This is what is called a transitive dependency. Read more about it in the free book Maven: The Complete Reference.
If I understand you right, you want to create a uber-jar containing all dependencies, right ?
Please refer to this question How can I create an executable JAR with dependencies using Maven?
In the second project's POM file, specify the first projects maven co-ordinates (groupId,artifactId,version,packaging) under the 'dependency' section. It will transitively acquire all the dependent artifacts.
Although it is possible in Maven to generate a standalone jar with all its dependencies. For that purpose, you can use the maven-shade-plugin. ( Reference )
There are two ways you are create a fat jar. You include the jar itself in the jar of dependent. You will not have much control in this case and the maven assembly plugin would do the work. Alternatively, you can unzip the jar and zip everything together to create the new jar. You have to decide which one best suits you. If you have multiple versions of same class, then include the whole jar in the new jar would help, but if the versions are coherent, it's best to create a jar by unzipping and zipping everything. For the second procedure, I recommend using the maven shade plugin to create uber jar.
I've just recently started doing Java development and I picked up Maven2 for dependency management and project task automation.
One peculiar issue I've stumbled upon, that I haven't been able to fully understand, is that for certain artifacts you need to configure exclusions for their dependencies, otherwise you get a Maven Missing artifact groupId:artifactId:version:lifecycle error. I've tried creating a Spring MVC project from the supplied STS Spring project templates and the Maven POM contained exclusions for log4j, which, when removed, would produce an error.
So what do I do when I manually add a dependency and get the missing artifact error for some of it's dependencies. Do I just jump and add them to the list of exclusions or should I be more careful about it?
And why does this happen? I'm assuming it may be perhaps that an artifact has a dependency of a certain version and another artifact has the same dependency of a different version, where both can't exist on the classpath or is it something else I'm missing?
You would configure exclusions if that particular dependency is being supplied elsewhere, either explicitly in your POM, or by another dependency.
If I got an "artifact not found" message my first thought would not be to exclude it, but to find out where it's required, then add it in the relevant scope to my POM.