exists-maven-plugin

Check if a maven artifact exists. Designed around the use case of skipping deployment if the stable
version already exists.

Requirements

• At least Maven 3.9.4
• At least Java 17

Goals

There are two goals: local
checks if the just built artifact is already in the local repository;
and remote checks if the
just built artifact is already in the remote repository.

Mojo details at plugin info

Parameters

Most parameters can be set with a maven property **exists.**_<parameter_name>_. e.g. skip
parameter can be set from command line using -Dexists.skip=true.

In the following table p: indicates the default constituent properties are prefixed with
project. and dm: indicates the default constituent properties are prefixed with
project.distributionManagement. e.g. for artifact parameter, the full default is
${project.artifactId}-${project.version}.${project.packaging}

Parameter	Default	Description
artifact	p:${artifactId}-${version}.${packaging}	The artifact within the project to query
cmpChecksum	false	Compare checksums of artifacts
failIfExists	false	Fail the build if the artifact already exists
failIfNotExists	false	Fail the build if the artifact does not exist
failIfNotMatch	false	Fail the build if the artifact exists and cmpChecksum is set and checksums do not match
lastSnapshotTime		The property to set with the timestamp of the last snapshot install / deploy
project	p:${groupId}:${artifactId}:${packaging}:${version}	The project within the repository to query
classifier		The classifier to use for checking the repository, e.g. 'tests'
property	${maven.deploy.skip} or ${maven.install.skip}	The property to receive the result of the query
repository	dm:${repository.url}	For remote goal, the repository to query for artifacts
requireGoal		Execute goal only if requireGoal value matches one of the maven command line goals
serverId	dm:${repository.id}	For remote goal, the server ID to use for authentication and proxy settings
skip	false	Skip executing the plugin
skipIfSnapshot	true	Skip the query if the project ends with -SNAPSHOT
snapshotRepository	dm:${snapshotRepository.url}	For remote goal, the repository to query for snapshot artifacts
snapshotServerId	dm:${snapshotRepository.id}	For remote goal, the server ID to use for snapshot authentication and proxy settings
userProperty	false	If the property should be set as a user property, to be available in child projects

Typical Use

xmlCopy

<build>
  <plugins>

    <plugin>
      <groupId>org.honton.chas</groupId>
      <artifactId>exists-maven-plugin</artifactId>
      <version>0.15.2</version>
      <executions>
        <execution>
          <goals>
            <goal>remote</goal>
          </goals>
        </execution>
      </executions>
    </plugin>

  </plugins>
</build>

How This Plugin Determines Location of Artifact

This plugin will log the resolved location of the artifact being checked for existence.

Resolved Location

The maven2 repository layout places an artifact
at a location based on the artifact's GAV

${repository root}/${groupId as directory}/${artifactId}/${version}/${artifactId}-${version}[-${classifier}].${extension}

Repository Root

settings.xml has properties to
locate a repository root.

The local repository root is defined by the settings.xml <settings><localRepository> element and
has default of ~.m2/reposistory.

The remote repository id is defined by the artifact's pom
<distributionManagement><repository><url> element for non-snapshot artifacts and
<distributionManagement><snapshotRepository><url> element for snapshot artifacts. This id should
match an id of a <repository> element in your pom's
<repositories> or from any active profiles in
the settings.xml. (The repository with the id of central is found in maven's
super pom).
The url in the matched <repository> element defines the remote repository root url.

Repository Path

• ${groupId}, ${artifactId}, ${version}, and ${packaging} are defined by this plugin's
  <configuration><project> element. This element is a GA[P]V. The default value of ${project}
  is interpolated from pom's project settings: ${groupId}:${artifactId}:${packaging}:${version}
• Any period ('.') in the ${groupId} of the artifact is replaced with a slash (/) to obtain
  ${groupId as directory}
• ${artifactId} and ${version} are used "as is"
• ${artifactId}-${version} is used "as is" for non-snapshot artifacts. ${artifactId}-${version}
  is appended with the latest build time for snapshot artifacts
• ${classifier} is defined by this plugin's <configuration><classifier> element. If not defined,
  the classifier is determined by consulting the maven built-in artifact handlers.
• ${extension} is defined through a heuristic based on ${packaging}

File Extension

If ${packaging} matches one of the built-in
Artifact Handler types,
${extension} is defined by that artifact handler. Otherwise, Custom Packaging
configuration determines the extension.

How This Plugin Determines if Builds are the "Same"

There are two strategies to determine if a maven artifacts are the "same" as what the project just
built: version comparison, and checksum comparison. By default, this plugin uses version comparison.
Version comparison simply checks if the group:artifact:version matches an artifact in the local or
remote repository. This simple check will not catch the situation where the developer has failed to
update the version in pom.xml.

Alternatively, when <cmpChecksum> is true, this plugin compares the checksum of the local or
remote
artifact with the just built artifact. Checksum comparison requires that the maven build be
reproducible. Without specific configuration, maven builds are not reproducible. See
Configuring for Reproducible Builds
for details on making your build reproducible.

Custom Packaging

If your build uses a custom packaging, (not one of the
Default Artifact Handlers),
and the file extension does not match the packaging then you need to specify a
<configuration><packageExtension><$packaging> element. e.g. for content-package packaging
specify a zip extension with the following configuration:

xmlCopy

<pluginManagement>
  <plugins>

    <plugin>
      <groupId>org.honton.chas</groupId>
      <artifactId>exists-maven-plugin</artifactId>
      <version>0.15.2</version>
      <configuration>
        <packageExtension>
          <content-package>zip</content-package>
        </packageExtension>
      </configuration>
    </plugin>

  </plugins>
</pluginManagement>

Snapshot builds

When checking snapshot builds against a remote/local repository, the last deployed/installed
snapshot of the correct version will be matched. Optionally, you can configure a property with
the lastSnapshotTime parameter which will receive the build timestamp. If you need additional date
math on the timestamp value, open a feature request with your use case.

Preventing failures of remote goal

Consider the scenario where there is an artifact that can only be deployed from a specific build
server to a corporate repository with a specialized workflow that ensures various security and
license policies. The exists-maven-plugin remote goal is also used to avoid duplicate deployments.

Running maven with the install phase will cause the exists-maven-plugin to execute the remote
task. This might fail for various reasons; including the developer laptop is not connected to the
internet, or the corporate repository is only available to specific build machines.

We could change the binding of the remote goal to the deploy phase. However, the
maven-deploy-plugin's deploy goal will run before exists-maven-plugin's remote goal because
"When multiple executions are given that match a particular phase, they are executed in the order
specified in the POM, with inherited executions running first."

The solution is to leave the remote goal bound to the install phase and add a requireGoal
configuration:

xmlCopy

<configuration>
  <!-- run only if deploy goal is specified in maven command line -->
  <requireGoal>deploy</requireGoal>
</configuration>