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Coming from npm/yarn background, for each and every project we will have node_modules which holds all the dependencies and libraries, if we wish to reset our project from clean state, we can always delete the entire node_modules and reinstall the libraries.

rm -rf node_modules/ && yarn cache clean && yarn install

Now trying to learn Java and trying out Maven, correct me if I'm wrong, we define the dependencies on pom.xml, which essentially the same as package.json on yarn/npm, and the downloaded dependencies will be stored on /target?

Is /target equals to node_modules and hence I can actually delete entire /target and restart the downloading process?

Isaac
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  • Possible duplicate of [Force re-download of release dependency using Maven](https://stackoverflow.com/questions/7959499/force-re-download-of-release-dependency-using-maven) – Starmixcraft Apr 16 '19 at 11:43
  • You shouldn't normally need to do this, maven dependencies are versioned, and except for snapshots they will be stable and cannot change. – Mark Rotteveel Apr 19 '19 at 14:47

5 Answers5

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The dependencies are not stored in target, but in .m2/repository in your user directory. This is the so-called local repository. It also holds all artifacts build on that computer/account.

You can delete it if necessary and only lose your local builds.

The target directory, on the other hand, gathers the (intermediate and final) results of a build. It can also be deleted, usually by using mvn clean.

J Fabian Meier
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  • But `m2` is in user directory, which means if my machine have 5 individual projects, all 5 projects' dependencies will be sharing this `m2` directory? – Isaac Apr 16 '19 at 11:46
  • Yes. It is a kind of cache, so you can share it as long as you do not run builds of different projects in parallel. – J Fabian Meier Apr 16 '19 at 11:47
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You can delete the .m2 folder lying in the below location somewhat and then do update maven project.You can also do (Force update of snapshots/releases").See this answer -here

Edit-As JF suggested ,the folder also contains the settings.xml ,A file that contains global settings for all maven executions,which you might not want to delete ,so you can just remove the repository folder,and reinstall your dependencies.

Unix/Mac OS X – ~/.m2/repository
Windows – C:\Users\{your-username}\.m2\repository
Shubham Dixit
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    Be careful: The `.m2` folder can also contain the `settings.xml` which you do not want to delete. – J Fabian Meier Apr 16 '19 at 11:41
  • You can also use `mvn dependency:purge-local-Repository` https://maven.apache.org/plugins/maven-dependency-plugin/examples/purging-local-repository.html – eckes Apr 17 '19 at 20:38
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you can re-install the maven dependencies using the following command:

mvn dependency:purge-local-repository

Noman ali abbasi
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there is no node_modles equivalent for maven, there is a central local repository maintained .m2/repository folder in per system.

Maven first search for the dependency in that local repo if not found then goes to maven central.

So if you want to delete your local cashed repository you can just simply delete all the folders in .m2/repository folder.

Then maven will not found the dependencies locally and will go for outside which is maven central.

And target contains the build artifact for each project. And mvn clean install command will execute the two lifecycle phases clean and install. To run install, maven will run all the phases preceding install in the default maven lifecycle.

For further reference .

build life cycle

Moshiour
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  • If I have 5 projects, all sharing the same `m2` repo, deleting folders in `m2` means I will be forced to perform re-download for each and every other 4 projects? – Isaac Apr 16 '19 at 11:49
  • For example if you use dependency com.example.something version:0.0.1 then no matter how many projects uses that exact version will get that from m2 . All of your projects will use that version from your m2 local repo. – Moshiour Apr 16 '19 at 11:51
  • Nö only the first build which needs a file will re-download it @isaac – eckes Apr 16 '19 at 12:39
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I'm still fairly new with Maven but I believe this will explain what your asking.

  1. When you set up your local repository for files/packages that are downloaded based on your POM dependencies they will be stored there and not in your 'target' folder.
  2. The target folder is used to house all of your java files as well as the dependency files you specified in your pom but these are copies from your 'repository' folder that is setup on your local box.
  3. When you run clean on your machine it will remove all the files in the 'target' folder. Your originally downloaded dependencies will remain in the 'repository' directory that you setup.
edjm
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