my Java Project uses a "/libs" folder containing ~100 .jar files. Almost all of them are not in an official maven repository.
1.) In the moment I manually added to whole folder to the classpath with my Eclipse IDE. That enables to compile and run the App using the Eclipse IDE. But if I want to maven to compile and create jar-with-dependencies, maven of course does not know about the "/libs" folder.
2.) I know that I can add a jar file to my local maven repo with mvn install:install-file but this would take a very long time because I would also have to open every jar and find the whole package name to insert as '-DgroupId' and the Name of the Main Class to add as '-DartifactId'
3.) My Questions:
3.1) Is there an easy way to let maven just include all jars in a folder like I did with my Eclipse IDE? I know that would break the principle of maven that every jar is identified with group and artifact id, but it would be a quick solution.
3.2) If it is not possible to add a folder with jars as a dependency in maven, is there a faster way to add a jar file into a local repo. It would be easier if there is a maven command where groupId and artifactId are automatically discovered by the jar that I do not have to open every jar file and find the Main Class and its classpath
Quick answer: No.
In the past, I have written a script for that because there is not support in Maven for this.
Related
I have a Java program in IntelliJ which has a pom.xml and uses Maven. The packages were downloaded and currently they are found by IntelliJ.
I'm a little confused though because the Maven repository is not part of the CLASSPATH as far as I can tell. So does IntelliJ just do a bit of magic where it looks into its Maven repository to find the packages? (I think that IntelliJ has its own Maven repo. I separately have Maven 3 installed, but I think it isn't using it.)
But more generally: If you build a JAR using Maven then I guess it will put the dependencies in the JAR where the Java program can find them, so there won't be a problem. But if you just run a Java program directly, do you need to add the Maven repository to your classpath or does something else happen?
Thanks for any information you can provide to lessen my confusion :)
When you start the program from IntelliJ using a runtime configuration for your main() method IntelliJ constructs the classpath from all the project dependencies. You can see this in the Run window, the first log line is the java command used to start the main(). It's a long line but it usually looks similar to:
java -javaagent:/opt/idea/idea-IC-173.3727.127/lib/idea_rt.jar=40165:/opt/infra/idea/idea-IC-173.3727.127/bin -Dfile.encoding=UTF-8 -classpath /home/ [...]
IntelliJ constructs the -classpath argument adding both the module target directory and the Maven dependencies referenced from the local Maven repository.
When you package the project using Maven mvn clean package usually it becomes a standalone JAR with just your code (unless you changed the defaults). Now you have a few choices how to provide dependencies needed to start your main():
Provide them using -classpath parameter just like IntelliJ.
Add maven-shade-plugin and use shade goal to the build a runnable Uber JAR. This creates a fat JAR which doesn't require -classpath.
Use some other Maven plugin to perform point 2 e.g. Spring Boot spring-boot:repackage goal.
All the required dependencies, defined in the pom.xml file(s), are downloaded from Maven Central (or others if configured) to the local Maven repository. That repository is located at <user home>/.m2/repository.
Maven generates/calculates a dependency tree to know all the required dependencies for the project. (you can also dump that tree with the command mvn dependency:tree. I always pipe the result to a file, because the tree can be large mvn dependency:tree > deptree.txt). Maven put them all on the classpath when executing a maven command like mvn compile
IntelliJ also use/calculate the dependency tree and add all the jar files to the projects classpath (point to the files in the <user home>/.m2/repository folder). You can see them all in the list with External Libraries, and they will be used / on the classpath for compilation and running the application.
When building a JAR file the dependencies are NOT added to the JAR. Only the bytecode (java classes) and resources from your own project are packaged into the JAR file. (Source files can also be packaged if you configure that)
By adding a Maven plugin (maven-shade-plugin) you can configure your project to also pack dependencies into the JAR. SpringBoot projects also will do that.
Could anyone would be so kind and explain how to make a single jar file with all maven dependencies in Netbeans Maven Java Application? In Eclipse user can Export to Runnable jar file and select Package required libraries into generated JAR, so all dependencies within project comes in created jar file. In Netbeans there is no such option.
I have checked other answers, but the only thing i understand is that I have to add code to Build.xml file which is not even in the project.
The last time I had to do this I used the Maven Shade Plugin. It allows you to create a single JAR file and also handles dependency clashes.
A simpler solution (which doesn't handle dependency clashes) is to use the Maven Assembly Plugin.
Note that these are pure Maven solutions which should work in any IDE.
After running Maven - clean, I see sub folders in my M2_REPO folder. junit.jar was created in M2_REPO/junit/junit/4.11/ alone with some other files. Because of this sub folder structure, eclipse is not able to recognize the junit.jar file. What am I missing?
You're looking in the wrong directory. Eclipse shouldn't read the jars directly from this directory, it is the local cache of what maven manages.
The pom.xml is where you should put your dependencies, and eclipse will then use the maven libraries to get the required jar file, put it on the build path, and possibly cache it in the directory you are looking at.
Note that if you want the junit jar file for testing purposes, the typical file in src/main/java will not see it, because testing source code goes in src/test/java.
This means that maven provides (through the libraries) (at least) two classpaths. One for typical compilation and one for test compilation and execution. Adding in a <dependency> tag section puts it on the compilation and run paths; but, to make it "test only" you need a nested <scope> tag.
Maven correctly is creating those directories the first time it tries to acquire those artifacts.
For integrating maven and eclipse, try running mvn eclipse:eclipse
This should enable eclipse to see the jars maven has downloaded.
That is the path of the local M2 repository and the sub-folder structure is exactly how it should look.
Make sure that you import the project in eclipse as a maven project by doing
File -> Import -> Maven -> Existing maven project
I have two projects in Eclipse, the first project depends on maven, the second project which dependent on the first one does NOT depend on maven.
The first project downloads external libraries like jar files and natives to the .m2 maven folder. However the second project gives a ClassNotFoundException since it cant find the jar files and the native files from the first project.
Is it possible to link these downloaded jars+dlls with the second project without having to reference in the build path->libraries in the second project properties?
I would appreciate any help.
In your Maven project, use Assembly plugin to create an Uber-jar that contains the project build artifact and all its dependencies (mvn assembly:assembly -DdescriptorId=jar-with-dependencies). Then, reference that from project #2, either with a relative path or by using an ant build task to copy it into your other project's lib directory (assuming you have such a directory). Also, although it's frowned upon, you could configure the assembly plugin so that your Uber jar artifact always has the same finalName.
Is it possible to link these downloaded jars+dlls with the second project without having to reference in the build path->libraries in the second project properties?
I don't think so.
But maybe you could create a 3rd project (which is a Maven project) that depends on the first one, and on the JAR (or whatever) file created by the 2nd one as a non-repository dependency.
Having said that, anything you do is going to be a bit of a hack. You'd be better of either turning the 2nd project into a proper Maven project, or creating a custom build script that manually pulls the 2nd project's dependencies from somewhere. (I think that Ivy could help you with that ... assuming you use Ant in the 2nd project.)
I have added to my pom.xml a section that specifies the mainClass and allows it to essentially create an executable jar. I have included a bunch of dependencies that maven manages as well. It executes fine, but fails to run when it gets to a section of code that needs to know the location of a jar package that was made inhouse by somebody (i.e., not from Maven). In the project in eclipse I had put the jar in src/lib and my code is in src/main/java. I had to select properties and Java Build Path and specify there the src/lib location for the jar to get it to even compile. However, trying to run java -jar name.jar has it fail and complain because it fails to import the classes from the src/lib jar. Since it is not a maven thing, how to I make sure this is a dependency for this project and that it is seen on the project's classpath?
The thing with maven is that maven has to control all of the dependencies and that includes this jar you want to reference. That doesn't mean that you have to build that other jar using maven, you could mvn install it in your local repository or use a tool like Artifactory to put it in a private remote repository. I know that installing regular jars via Artifactory creates a pom file for the jar and from then on you can treat the jar like any other maven dependency.