Maven packages in the package registry

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Publish Maven artifacts in your project's package registry. Then, install the packages whenever you need to use them as a dependency.

For documentation of the specific API endpoints that the Maven package manager client uses, see the Maven API documentation.

Supported clients:

• mvn. Learn how to build a Maven package.
• gradle. Learn how to build a Gradle package.
• sbt.

Publish to the GitLab package registry

Authenticate to the package registry

You need a token to publish a package. There are different tokens available depending on what you're trying to achieve. For more information, review the guidance on tokens.

Create a token and save it to use later in the process.

Do not use authentication methods other than the methods documented here. Undocumented authentication methods might be removed in the future.

Edit the client configuration

Update your configuration to authenticate to the Maven repository with HTTP.

Custom HTTP header

You must add the authentication details to the configuration file for your client.

::Tabs

:::TabTitle mvn

NOTE: The <name> field must be named to match the token you chose.

Add the following section to your settings.xml file.

<settings>
  <servers>
    <server>
      <id>gitlab-maven</id>
      <configuration>
        <httpHeaders>
          <property>
            <name>REPLACE_WITH_NAME</name>
            <value>REPLACE_WITH_TOKEN</value>
          </property>
        </httpHeaders>
      </configuration>
    </server>
  </servers>
</settings>

:::TabTitle gradle

NOTE: The <name> field must be named to match the token you chose.

In your GRADLE_USER_HOME directory, create a file gradle.properties with the following content:

gitLabPrivateToken=REPLACE_WITH_YOUR_TOKEN

Add a repositories section to your build.gradle file:

• In Groovy DSL:

  repositories {
      maven {
          url "https://gitlab.example.com/api/v4/groups/<group>/-/packages/maven"
          name "GitLab"
          credentials(HttpHeaderCredentials) {
              name = 'REPLACE_WITH_NAME'
              value = gitLabPrivateToken
          }
          authentication {
              header(HttpHeaderAuthentication)
          }
      }
  }

• In Kotlin DSL:

  repositories {
      maven {
          url = uri("https://gitlab.example.com/api/v4/groups/<group>/-/packages/maven")
          name = "GitLab"
          credentials(HttpHeaderCredentials::class) {
              name = "REPLACE_WITH_NAME"
              value = findProperty("gitLabPrivateToken") as String?
          }
          authentication {
              create("header", HttpHeaderAuthentication::class)
          }
      }
  }

::EndTabs

Basic HTTP Authentication

You can also use basic HTTP authentication to authenticate to the Maven package registry.

::Tabs

:::TabTitle mvn

Add the following section to your settings.xml file.

<settings>
  <servers>
    <server>
      <id>gitlab-maven</id>
      <username>REPLACE_WITH_NAME</username>
      <password>REPLACE_WITH_TOKEN</password>
      <configuration>
        <authenticationInfo>
          <userName>REPLACE_WITH_NAME</userName>
          <password>REPLACE_WITH_TOKEN</password>
        </authenticationInfo>
      </configuration>
    </server>
  </servers>
</settings>

:::TabTitle gradle

In your GRADLE_USER_HOME directory, create a file gradle.properties with the following content:

gitLabPrivateToken=REPLACE_WITH_YOUR_TOKEN

Add a repositories section to your build.gradle.

• In Groovy DSL:

  repositories {
      maven {
          url "https://gitlab.example.com/api/v4/groups/<group>/-/packages/maven"
          name "GitLab"
          credentials(PasswordCredentials) {
              username = 'REPLACE_WITH_NAME'
              password = gitLabPrivateToken
          }
          authentication {
              basic(BasicAuthentication)
          }
      }
  }

• In Kotlin DSL:

  repositories {
      maven {
          url = uri("https://gitlab.example.com/api/v4/groups/<group>/-/packages/maven")
          name = "GitLab"
          credentials(BasicAuthentication::class) {
              username = "REPLACE_WITH_NAME"
              password = findProperty("gitLabPrivateToken") as String?
          }
          authentication {
              create("basic", BasicAuthentication::class)
          }
      }
  }

:::TabTitle sbt

Authentication for SBT is based on basic HTTP Authentication. You must to provide a name and a password.

NOTE: The name field must be named to match the token you chose.

To install a package from the Maven GitLab package registry by using sbt, you must configure a Maven resolver. If you're accessing a private or an internal project or group, you need to set up credentials. After configuring the resolver and authentication, you can install a package from a project, group, or namespace.

In your build.sbt, add the following lines:

resolvers += ("gitlab" at "<endpoint url>")

credentials += Credentials("GitLab Packages Registry", "<host>", "<name>", "<token>")

In this example:

• <endpoint url> is the endpoint URL. Example: https://gitlab.example.com/api/v4/projects/<project_id>/packages/maven.
• <host> is the host present in the <endpoint url> without the protocol scheme or the port. Example: gitlab.example.com.
• <name> and <token> are explained in the table above.

::EndTabs

Naming convention

You can use one of three endpoints to install a Maven package. You must publish a package to a project, but the endpoint you choose determines the settings you add to your pom.xml file for publishing.

The three endpoints are:

• Project-level: Use when you have a few Maven packages and they are not in the same GitLab group.
• Group-level: Use when you want to install packages from many different projects in the same GitLab group. GitLab does not guarantee the uniqueness of package names within the group. You can have two projects with the same package name and package version. As a result, GitLab serves whichever one is more recent.
• Instance-level: Use when you have many packages in different GitLab groups or in their own namespace.

For the instance-level endpoint, ensure the relevant section of your pom.xml in Maven looks like this:

  <groupId>group-slug.subgroup-slug</groupId>
  <artifactId>project-slug</artifactId>

Only packages that have the same path as the project are exposed by the instance-level endpoint.

Endpoint URLs

Edit the configuration file for publishing

You must add publishing details to the configuration file for your client.

::Tabs

:::TabTitle mvn

No matter which endpoint you choose, you must have:

• A project-specific URL in the distributionManagement section.
• A repository and distributionManagement section.

The relevant repository section of your pom.xml in Maven should look like this:

<repositories>
  <repository>
    <id>gitlab-maven</id>
    <url><your_endpoint_url></url>
  </repository>
</repositories>
<distributionManagement>
  <repository>
    <id>gitlab-maven</id>
    <url>https://gitlab.example.com/api/v4/projects/<project_id>/packages/maven</url>
  </repository>
  <snapshotRepository>
    <id>gitlab-maven</id>
    <url>https://gitlab.example.com/api/v4/projects/<project_id>/packages/maven</url>
  </snapshotRepository>
</distributionManagement>

• The id is what you defined in settings.xml.
• The <your_endpoint_url> depends on which endpoint you choose.
• Replace gitlab.example.com with your domain name.

:::TabTitle gradle

To publish a package by using Gradle:

1. Add the Gradle plugin maven-publish to the plugins section:

   • In Groovy DSL:

     plugins {
         id 'java'
         id 'maven-publish'
     }

   • In Kotlin DSL:

     plugins {
         java
         `maven-publish`
     }

2. Add a publishing section:

   • In Groovy DSL:

     publishing {
         publications {
             library(MavenPublication) {
                 from components.java
             }
         }
         repositories {
             maven {
                 url "https://gitlab.example.com/api/v4/projects/<PROJECT_ID>/packages/maven"
                 credentials(HttpHeaderCredentials) {
                     name = "REPLACE_WITH_TOKEN_NAME"
                     value = gitLabPrivateToken // the variable resides in $GRADLE_USER_HOME/gradle.properties
                 }
                 authentication {
                     header(HttpHeaderAuthentication)
                 }
             }
         }
     }

   • In Kotlin DSL:

     publishing {
         publications {
             create<MavenPublication>("library") {
                 from(components["java"])
             }
         }
         repositories {
             maven {
                 url = uri("https://gitlab.example.com/api/v4/projects/<PROJECT_ID>/packages/maven")
                 credentials(HttpHeaderCredentials::class) {
                     name = "REPLACE_WITH_TOKEN_NAME"
                     value =
                         findProperty("gitLabPrivateToken") as String? // the variable resides in $GRADLE_USER_HOME/gradle.properties
                 }
                 authentication {
                     create("header", HttpHeaderAuthentication::class)
                 }
             }
         }
     }

::EndTabs

Publish a package

WARNING: Using the DeployAtEnd option can cause an upload to be rejected with 400 bad request {"message":"Validation failed: Name has already been taken"}. For more details, see issue 424238.

After you have set up the authentication and chosen an endpoint for publishing, publish a Maven package to your project.

::Tabs

:::TabTitle mvn

To publish a package by using Maven:

mvn deploy

If the deploy is successful, the build success message should be displayed:

...
[INFO] BUILD SUCCESS
...

The message should also show that the package was published to the correct location:

Uploading to gitlab-maven: https://example.com/api/v4/projects/PROJECT_ID/packages/maven/com/mycompany/mydepartment/my-project/1.0-SNAPSHOT/my-project-1.0-20200128.120857-1.jar

:::TabTitle gradle

Run the publish task:

gradle publish

Go to your project's Packages and registries page and view the published packages.

:::TabTitle sbt

Configure the publishTo setting in your build.sbt file:

publishTo := Some("gitlab" at "<endpoint url>")

Ensure the credentials are referenced correctly. See the sbt documentation for more information.

To publish a package using sbt:

sbt publish

If the deploy is successful, the build success message is displayed:

[success] Total time: 1 s, completed Jan 28, 2020 12:08:57 PM

Check the success message to ensure the package was published to the correct location:

[info]  published my-project_2.12 to https://gitlab.example.com/api/v4/projects/PROJECT_ID/packages/maven/com/mycompany/my-project_2.12/0.1.1-SNAPSHOT/my-project_2.12-0.1.1-SNAPSHOT.pom

::EndTabs

Install a package

To install a package from the GitLab package registry, you must configure the remote and authenticate. When this is completed, you can install a package from a project, group, or namespace.

If multiple packages have the same name and version, when you install a package, the most recently-published package is retrieved.

In case there are not enough permissions to read the most recently-published package than 403 Forbidden is returning.

::Tabs

:::TabTitle mvn

To install a package by using mvn install:

1. Add the dependency manually to your project pom.xml file. To add the example created earlier, the XML would be:

   <dependency>
     <groupId>com.mycompany.mydepartment</groupId>
     <artifactId>my-project</artifactId>
     <version>1.0-SNAPSHOT</version>
   </dependency>

2. In your project, run the following:

   mvn install

The message should show that the package is downloading from the package registry:

Downloading from gitlab-maven: http://gitlab.example.com/api/v4/projects/PROJECT_ID/packages/maven/com/mycompany/mydepartment/my-project/1.0-SNAPSHOT/my-project-1.0-20200128.120857-1.pom

You can also install packages by using the Maven dependency:get command directly.

1. In your project directory, run:

   mvn dependency:get -Dartifact=com.nickkipling.app:nick-test-app:1.1-SNAPSHOT -DremoteRepositories=gitlab-maven::::<gitlab endpoint url>  -s <path to settings.xml>

   • <gitlab endpoint url> is the URL of the GitLab endpoint.
   • <path to settings.xml> is the path to the settings.xml file that contains the authentication details.

NOTE: The repository IDs in the command(gitlab-maven) and the settings.xml file must match.

The message should show that the package is downloading from the package registry:

Downloading from gitlab-maven: http://gitlab.example.com/api/v4/projects/PROJECT_ID/packages/maven/com/mycompany/mydepartment/my-project/1.0-SNAPSHOT/my-project-1.0-20200128.120857-1.pom

:::TabTitle gradle

To install a package by using gradle:

1. Add a dependency to build.gradle in the dependencies section:

   • In Groovy DSL:

     dependencies {
         implementation 'com.mycompany.mydepartment:my-project:1.0-SNAPSHOT'
     }

   • In Kotlin DSL:

     dependencies {
         implementation("com.mycompany.mydepartment:my-project:1.0-SNAPSHOT")
     }

2. In your project, run the following:

   gradle install

:::TabTitle sbt

To install a package by using sbt:

1. Add an inline dependency to build.sbt:

   libraryDependencies += "com.mycompany.mydepartment" % "my-project" % "8.4"

2. In your project, run the following:

   sbt update

::EndTabs

CI/CD integration for Maven packages

You can use CI/CD to automatically build, test, and publish Maven packages. The examples in this section cover scenarios like:

• Multi-module projects
• Versioned releases
• Conditional publishing
• Integration with code quality and security scans

You can adapt and combine these examples to suit your specific project needs.

Remember to adjust the Maven version, Java version, and other specifics according to your project requirements. Also, make sure you properly configured the necessary credentials and settings for publishing to the GitLab package registry.

Basic Maven package build and publish

This example configures a pipeline that builds and publishes a Maven package:

image: maven:3.8.5-openjdk-17

variables:
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

cache:
  paths:
    - .m2/repository/
    - target/

stages:
  - build
  - test
  - publish

build:
  stage: build
  script:
    - mvn $MAVEN_CLI_OPTS compile

test:
  stage: test
  script:
    - mvn $MAVEN_CLI_OPTS test

publish:
  stage: publish
  script:
    - mvn $MAVEN_CLI_OPTS deploy
  rules:
    - if: $CI_COMMIT_BRANCH == "main"

Multi-module Maven project with parallel jobs

For larger projects with multiple modules, you can use parallel jobs to speed up the build process:

image: maven:3.8.5-openjdk-17

variables:
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

cache:
  paths:
    - .m2/repository/
    - target/

stages:
  - build
  - test
  - publish

build:
  stage: build
  script:
    - mvn $MAVEN_CLI_OPTS compile

test:
  stage: test
  parallel:
    matrix:
      - MODULE: [module1, module2, module3]
  script:
    - mvn $MAVEN_CLI_OPTS test -pl $MODULE

publish:
  stage: publish
  script:
    - mvn $MAVEN_CLI_OPTS deploy
  rules:
    - if: $CI_COMMIT_BRANCH == "main"

Versioned releases with tags

This example creates versioned releases when a tag is pushed:

image: maven:3.8.5-openjdk-17

variables:
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

cache:
  paths:
    - .m2/repository/
    - target/

stages:
  - build
  - test
  - publish
  - release

build:
  stage: build
  script:
    - mvn $MAVEN_CLI_OPTS compile

test:
  stage: test
  script:
    - mvn $MAVEN_CLI_OPTS test

publish:
  stage: publish
  script:
    - mvn $MAVEN_CLI_OPTS deploy
  only:
    - main

release:
  stage: release
  script:
    - mvn versions:set -DnewVersion=${CI_COMMIT_TAG}
    - mvn $MAVEN_CLI_OPTS deploy
  rules:
    - if: $CI_COMMIT_TAG

Conditional publishing based on changes

This example publishes packages only when certain files are changed:

image: maven:3.8.5-openjdk-17

variables:
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

cache:
  paths:
    - .m2/repository/
    - target/

stages:
  - build
  - test
  - publish

build:
  stage: build
  script:
    - mvn $MAVEN_CLI_OPTS compile

test:
  stage: test
  script:
    - mvn $MAVEN_CLI_OPTS test

publish:
  stage: publish
  script:
    - mvn $MAVEN_CLI_OPTS deploy
  only:
    - main
  rules:
    - changes:
      - pom.xml
      - src/**/*

Integration with code quality and security scans

This example integrates code quality checks and security scans into the pipeline:

image: maven:3.8.5-openjdk-17

variables:
  MAVEN_CLI_OPTS: "-s .m2/settings.xml --batch-mode"
  MAVEN_OPTS: "-Dmaven.repo.local=.m2/repository"

include:
  - template: Security/SAST.gitlab-ci.yml
  - template: Code-Quality.gitlab-ci.yml

cache:
  paths:
    - .m2/repository/
    - target/

stages:
  - build
  - test
  - quality
  - publish

build:
  stage: build
  script:
    - mvn $MAVEN_CLI_OPTS compile

test:
  stage: test
  script:
    - mvn $MAVEN_CLI_OPTS test

code_quality:
  stage: quality

sast:
  stage: quality

publish:
  stage: publish
  script:
    - mvn $MAVEN_CLI_OPTS deploy
  rules:
    - if: $CI_COMMIT_BRANCH == "main"

Helpful hints

Publishing a package with the same name or version

When you publish a package with the same name and version as an existing package, the new package files are added to the existing package. You can still use the UI or API to access and view the existing package's older assets.

To delete older package versions, consider using the Packages API or the UI.

Do not allow duplicate Maven packages

• Required role changed from Developer to Maintainer in GitLab 15.0.
• Required role changed from Maintainer to Owner in GitLab 17.0.

To prevent users from publishing duplicate Maven packages, you can use the GraphQl API or the UI.

In the UI:

1. On the left sidebar, select Search or go to and find your group.
2. Select Settings > Packages and registries.
3. In the Maven row of the Duplicate packages table, turn off the Allow duplicates toggle.
4. Optional. In the Exceptions text box, enter a regular expression that matches the names and versions of packages to allow.

Your changes are automatically saved.

Request forwarding to Maven Central

• Required role changed from Maintainer to Owner in GitLab 17.0.

FLAG: By default this feature is not available for self-managed. To make it available, an administrator can enable the feature flag named maven_central_request_forwarding. This feature is not available for GitLab.com or GitLab Dedicated users.

When a Maven package is not found in the package registry, the request is forwarded to Maven Central.

When the feature flag is enabled, administrators can disable this behavior in the Continuous Integration settings.

Maven forwarding is restricted to only the project level and group level endpoints. The instance level endpoint has naming restrictions that prevent it from being used for packages that don't follow that convention and also introduces too much security risk for supply-chain style attacks.

Additional configuration for mvn

When using mvn, there are many ways to configure your Maven project so that it requests packages in Maven Central from GitLab. Maven repositories are queried in a specific order. By default, Maven Central is usually checked first through the Super POM, so GitLab needs to be configured to be queried before maven-central.

To ensure all package requests are sent to GitLab instead of Maven Central, you can override Maven Central as the central repository by adding a <mirror> section to your settings.xml:

<settings>
  <servers>
    <server>
      <id>central-proxy</id>
      <configuration>
        <httpHeaders>
          <property>
            <name>Private-Token</name>
            <value><personal_access_token></value>
          </property>
        </httpHeaders>
      </configuration>
    </server>
  </servers>
  <mirrors>
    <mirror>
      <id>central-proxy</id>
      <name>GitLab proxy of central repo</name>
      <url>https://gitlab.example.com/api/v4/projects/<project_id>/packages/maven</url>
      <mirrorOf>central</mirrorOf>
    </mirror>
  </mirrors>
</settings>

Create Maven packages with GitLab CI/CD

After you have configured your repository to use the Package Repository for Maven, you can configure GitLab CI/CD to build new packages automatically.

::Tabs

:::TabTitle mvn

You can create a new package each time the default branch is updated.

1. Create a ci_settings.xml file that serves as Maven's settings.xml file.

2. Add the server section with the same ID you defined in your pom.xml file. For example, use gitlab-maven as the ID:

   <settings xmlns="http://maven.apache.org/SETTINGS/1.1.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.1.0 http://maven.apache.org/xsd/settings-1.1.0.xsd">
     <servers>
       <server>
         <id>gitlab-maven</id>
         <configuration>
           <httpHeaders>
             <property>
               <name>Job-Token</name>
               <value>${CI_JOB_TOKEN}</value>
             </property>
           </httpHeaders>
         </configuration>
       </server>
     </servers>
   </settings>

3. Make sure your pom.xml file includes the following. You can either let Maven use the predefined CI/CD variables, as shown in this example, or you can hard code your server's hostname and project's ID.

   <repositories>
     <repository>
       <id>gitlab-maven</id>
       <url>${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/maven</url>
     </repository>
   </repositories>
   <distributionManagement>
     <repository>
       <id>gitlab-maven</id>
       <url>${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/maven</url>
     </repository>
     <snapshotRepository>
       <id>gitlab-maven</id>
       <url>${CI_API_V4_URL}/projects/${CI_PROJECT_ID}/packages/maven</url>
     </snapshotRepository>
   </distributionManagement>

4. Add a deploy job to your .gitlab-ci.yml file:

   deploy:
     image: maven:3.6-jdk-11
     script:
       - 'mvn deploy -s ci_settings.xml'
     rules:
       - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

5. Push those files to your repository.

The next time the deploy job runs, it copies ci_settings.xml to the user's home location. In this example:

• The user is root, because the job runs in a Docker container.
• Maven uses the configured CI/CD variables.

:::TabTitle gradle

You can create a package each time the default branch is updated.

1. Authenticate with a CI job token in Gradle.

2. Add a deploy job to your .gitlab-ci.yml file:

   deploy:
     image: gradle:6.5-jdk11
     script:
       - 'gradle publish'
     rules:
       - if: $CI_COMMIT_BRANCH == $CI_DEFAULT_BRANCH

3. Commit files to your repository.

When the pipeline is successful, the Maven package is created.

::EndTabs

Version validation

The version string is validated by using the following regex.

\A(?!.*\.\.)[\w+.-]+\z

You can experiment with the regex and try your version strings on this regular expression editor.

Use different settings for snapshot and release deployments

To use different URLs or settings for snapshots and releases:

• In the <distributionManagement> section of your pom.xml file, define separate <repository> and <snapshotRepository> elements.

Useful Maven command-line options

There are some Maven command-line options that you can use when performing tasks with GitLab CI/CD.

• File transfer progress can make the CI logs hard to read. Option -ntp,--no-transfer-progress was added in 3.6.1. Alternatively, look at -B,--batch-mode or lower level logging changes.

• Specify where to find the pom.xml file (-f,--file):

  package:
    script:
      - 'mvn --no-transfer-progress -f helloworld/pom.xml package'

• Specify where to find the user settings (-s,--settings) instead of the default location. There's also a -gs,--global-settings option:

  package:
    script:
      - 'mvn -s settings/ci.xml package'

Supported CLI commands

The GitLab Maven repository supports the following CLI commands:

::Tabs

:::TabTitle mvn

• mvn deploy: Publish your package to the package registry.
• mvn install: Install packages specified in your Maven project.
• mvn dependency:get: Install a specific package.

:::TabTitle gradle

• gradle publish: Publish your package to the package registry.
• gradle install: Install packages specified in your Gradle project.

::EndTabs

Troubleshooting

While working with Maven packages in GitLab, you might encounter an issue. To resolve many common issues, try these steps:

• Verify authentication - Ensure your authentication tokens are correct and have not expired.
• Check permissions - Confirm you have the necessary permissions to publish or install packages.
• Validate Maven settings - Double-check your settings.xml file for correct configuration.
• Review GitLab CI/CD logs - For CI/CD issues, carefully examine the job logs for error messages.
• Ensure correct endpoint URLs - Verify you're using the correct endpoint URLs for your project or group.
• Use the -s option with mvn commands - Always run Maven commands with the -s option, for example, mvn package -s settings.xml. Without this option, authentication settings aren't applied, and Maven might fail to find packages.

Clear the cache

To improve performance, clients cache files related to a package. If you encounter issues, clear the cache with these commands:

::Tabs

:::TabTitle mvn

rm -rf ~/.m2/repository

:::TabTitle gradle

rm -rf ~/.gradle/caches # Or replace ~/.gradle with your custom GRADLE_USER_HOME

::EndTabs

Review network trace logs

If you are having issues with the Maven Repository, you may want to review network trace logs.

For example, try to run mvn deploy locally with a PAT token and use these options:

mvn deploy \
-Dorg.slf4j.simpleLogger.log.org.apache.maven.wagon.providers.http.httpclient=trace \
-Dorg.slf4j.simpleLogger.log.org.apache.maven.wagon.providers.http.httpclient.wire=trace

WARNING: When you set these options, all network requests are logged and a large amount of output is generated.

Verify your Maven settings

If you encounter issues within CI/CD that relate to the settings.xml file, try adding an additional script task or job to verify the effective settings.

The help plugin can also provide system properties, including environment variables:

mvn-settings:
  script:
    - 'mvn help:effective-settings'

package:
  script:
    - 'mvn help:system'
    - 'mvn package'

"401 Unauthorized" error when trying to publish a package

This usually indicates an authentication issue. Check that:

• Your authentication token is valid and has not expired.
• You're using the correct token type (personal access token, deploy token, or CI job token).
• The token has the necessary permissions (api, read_api, or read_repository).
• For Maven projects, you're using the -s option with your mvn commands (for example, mvn deploy -s settings.xml). Without this option, Maven won't apply the authentication settings from your settings.xml file, leading to unauthorized errors.

"400 Bad Request" error with message "Validation failed: Version is invalid"

GitLab has specific requirements for version strings. Ensure your version follows the format:

^(?!.*\.\.)(?!.*\.$)[0-9A-Za-z-]+(\.[0-9A-Za-z-]+)*(\+[0-9A-Za-z-]+)?$

For example, "1.0.0", "1.0-SNAPSHOT", and "1.0.0-alpha" are valid, but "1..0" or "1.0." are not.

"Artifact already exists" errors when publishing

This error occurs when you try to publish a package version that already exists. To resolve:

• Increment your package version before publishing.
• If you're using SNAPSHOT versions, ensure you're allowing SNAPSHOT overwrites in your configuration.

Published package not appearing in the UI

If you've just published a package, it might take a few moments to appear. If it still doesn't show:

• Verify you have the necessary permissions to view packages.
• Check that the package was successfully published by reviewing CI/CD logs or Maven output.
• Ensure you're looking in the correct project or group.

Maven repository dependency conflicts

Dependency conflicts can be resolved by:

• Explicitly defining versions in your pom.xml.
• Using Maven's dependency management section to control versions.
• Using the <exclusions> tag to exclude conflicting transitive dependencies.

"Unable to find valid certification path to requested target" error

This is typically a SSL certificate issue. To resolve:

• Ensure your JDK trusts the GitLab server's SSL certificate.
• If using a self-signed certificate, add it to the truststore of your JDK.
• As a last resort, you can disable SSL verification in Maven settings. Not recommended for production.

"No plugin found for prefix" pipeline errors

This usually means Maven can't find the plugin. To fix:

• Ensure the plugin is correctly defined in your pom.xml.
• Check that your CI/CD configuration is using the correct Maven settings file.
• Verify that your pipeline has access to all necessary repositories.