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mvn -pl <name> -am command

I have the following command, which I'm using to build a specific microservice (<ms-name>):
./mvnw -DskipTests clean install -pl <ms-name> -am
clean, instal, and -DskipTest are clear. But I don't understand what -pl and -am are doing.
logs:
[INFO] ------------------------------------------------------------------------
[INFO] Reactor Build Order:
[INFO]
[INFO] <utils-1> [jar]
[INFO] <utils-2> [jar]
[INFO] <ms-name> [jar]
and after it starts executing clean install on , , and in the end <ms-name>
I have checked the pom.xml but could not see the relations somewhere.
My question is: What are -pl and -am and where I can find this 'order' building relation between <ms-name>, <utils-1>, and <utils-2>?

From documentation,
-pl is,
Comma-delimited list of specified reactor projects to build instead of
all projects. A project can be specified by [groupId]:artifactId or
by its relative path
-am is,
If project list is specified, also build projects required by the list
where I can find this 'order' building relation ..?
It is handled by reactor (and internal program within maven) which collects all the available modules to build, sorts the projects into the correct build order and builds the selected projects in order.
To get understand more about maven reactor, here is a StackOverflow answer which is more detailed enough.
What is the "reactor" in Maven?

Facing Issue with Maven custom archtype

I'm trying to generate custom maven archtype, I'm trying below example to generate custom maven spring boot archtype:
Custom Maven Archtype
If I try to run the below maven generate command - works good
mvn archetype:generate \
-DarchetypeGroupId=com.romeh.spring-boot-archetypes \
-DarchetypeArtifactId=spring-boot-quickstart \
-DarchetypeVersion=1.0.0 \
-DgroupId=com.test \
-DartifactId=sampleapp \
-Dversion=1.0.0-SNAPSHOT \
-DinteractiveMode=false
But if I change the Group ID with my custom name - it started failing
For example if I change this from -DarchetypeGroupId=com.romeh.spring-boot-archetypes to -DarchetypeGroupId=com.test.spring-boot-archetypes
I'm getting below error message - if I change the group id.
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 01:26 min
[INFO] Finished at: 2018-04-19T11:45:36-04:00
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-archetype-plugin:3.0.1:generate (default-cli) on project spring-boot-quickstart: The desired archetype does not exist (com.test.spring-boot-archetypes:spring-boot-quickstart:1.0.0) -> [Help 1]
Please note that - before executing this command I've changed group id in pom.xml and archetype-catalog.xml as well.
Can you please help me to fix this issue - not sure what i'm doing wrong here.

You just should not do that. These properties
-DarchetypeGroupId=com.romeh.spring-boot-archetypes
-DarchetypeArtifactId=spring-boot-quickstart
-DarchetypeVersion=1.0.0
identifies the archetype; it's like when you have some JAR and you want to add it to your project you need to provide groupId, artifactId and version.
The same approach is used for archetypes! Archetypes are packaged up in a JAR and they consist of the archetype metadata which describes the contents of the archetype.
Those properties say Maven what archetype (like what JAR) it should run to generate your app skeleton. And if you change them - Maven won't just find the appropriate JAR in the repository.
Instead, you should modify:
-DgroupId=com.test
-DartifactId=sampleapp
-Dversion=1.0.0-SNAPSHOT
Those will be properties of your project generated by that archetype.

How are maven plugin aliases mapped

I am trying to understand what mvn clean:clean actually does.
mvn -B help:describe -Dcmd=clean
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building sample-one 1.0.0
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-help-plugin:2.2:describe (default-cli) # sample-one ---
[INFO] 'clean' is a lifecycle with the following phases:
* pre-clean: Not defined
* clean: org.apache.maven.plugins:maven-clean-plugin:2.5:clean
* post-clean: Not defined
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.689 s
[INFO] Finished at: 2015-12-10T10:20:16-08:00
[INFO] Final Memory: 9M/245M
[INFO] ------------------------------------------------------------------------
It appears to me that mvn clean:clean is same as doing mvn org.apache.maven.plugins:maven-clean-plugin:2.5:clean. Therefore I am assuming the first clean in mvn clean:clean is just an alias for org.apache.maven.plugins:maven-clean-plugin:2.5. Similarly mvn maven-surefire-plugin:2.12.4:test is same as mvn surefire:test.
So somehow, maven-surefire-plugin:2.12.4 seems to refer to surefire and org.apache.maven.plugins:maven-clean-plugin:2.5 to clean.
When I look at the effective-pom, I see the following
maven-surefire-plugin
2.12.4
default-test
test
test
maven-clean-plugin
2.5
default-clean
clean
clean
As you can see, the pom doesnt seem to define alias. So following are my questions
Is my understanding about plugin aliases correct
If my understanding about aliases is correct - a) how and where are they defined? b) Is there a way to list all aliases.

From official Maven documentation about plugins development:
Shortening the Command Line
There are several ways to reduce the amount of required typing:
If you need to run the latest version of a plugin installed in your local repository, you can omit its version number. So just use mvn sample.plugin:hello-maven-plugin:sayhi to run your plugin.
You can assign a shortened prefix to your plugin, such as mvn hello:sayhi. This is done automatically if you follow the convention of using ${prefix}-maven-plugin (or maven-${prefix}-plugin if the plugin is part of the Apache Maven project). You may also assign one through additional configuration - for more information see Introduction to Plugin Prefix Mapping.
Finally, you can also add your plugin's groupId to the list of groupIds searched by default. To do this, you need to add the following to your ${user.home}/.m2/settings.xml file:
<pluginGroups>
<pluginGroup>sample.plugin</pluginGroup>
</pluginGroups>
At this point, you can run the mojo with mvn hello:sayhi.
So, alias are not defined in the pom file but part of built-in mechanism of maven. Further details are also provided in the official documentation about Plugin Prefix Resolution.

Check for Updated Version of Maven [duplicate]

Is there a Maven plugin that allows you to check if there are newer versions of dependencies available in the repository?
Say, you are using dependency X with version 1.2. Now a new version of X is released with version 1.3. I'd like to know, based on the dependencies used in my project, which dependencies have newer versions available.

The Maven Versions plugin and it's display-dependency-updates mojo are what you're looking for:
mvn versions:display-dependency-updates
Here is what the output looks like:
[INFO] ------------------------------------------------------------------------
[INFO] Building Build Helper Maven Plugin
[INFO] task-segment: [versions:display-dependency-updates]
[INFO] ------------------------------------------------------------------------
[INFO] [versions:display-dependency-updates]
[INFO]
[INFO] The following dependency updates are available:
[INFO] org.apache.maven:maven-artifact ........................ 2.0 -> 2.0.9
[INFO] org.apache.maven:maven-plugin-api ...................... 2.0 -> 2.0.9
[INFO] org.apache.maven:maven-project ....................... 2.0.2 -> 2.0.9
[INFO] org.codehaus.plexus:plexus-utils ....................... 1.1 -> 1.5.6
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESSFUL
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 17 seconds
[INFO] Finished at: Fri Aug 15 10:46:03 IST 2008
[INFO] Final Memory: 10M/167M
[INFO] ------------------------------------------------------------------------

If you want to receive email notifications when newer artifacts versions are available on Maven Central you can create an account on artifact-listener and choose which artifact you want to follow.
You can either search manually for artifacts or directly upload your pom.xml.
You will periodically received notifications like this one (available in english and french for now) :

In projects with a large number of dependancies, you sometimes keep your versions in a properties section.
<properties>
<assertj.version>3.15.0</assertj.version>
<aws-sdk.version>1.11.763</aws-sdk.version>
<cxf.version>3.3.6</cxf.version>
In the case where you are only interested in updates to those versions, you can use the following command
mvn versions:display-property-updates
This gives a more condensed view and only returns the versions you need to update in the properties section.

The VersionEye Maven Plugin is doing the same: versioneye_maven_plugin.
VersionEye can notify you about new versions on Maven Repositories, too. It is a language agnostic tool and beside Java it supports 7 other languages. Beside the simple follow/notify feature it can also directly monitor GitHub and BitBucket repositories and notify your about out-dated dependencies in your projects.
There is also a REST JSON API, for tool integrations.
By the way, I'm the dude who started this project. Let me know if you have questions.

The ideal way to do it is to set dependency versions as properties in pom.xml and then running the below command to get the updated versions for your specific/custom dependencies.
<properties>
<java.version>1.8</java.version>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
<skip.tests>true</skip.tests>
<spring-cloud-gcp.version>1.2.3.RELEASE</spring-cloud-gcp.version>
<spring-cloud.version>Hoxton.SR6</spring-cloud.version>
<spring-cloud-stream-schema.version>2.2.1.RELEASE</spring-cloud-stream-schema.version>
<confluent.version>5.5.1</confluent.version>
<avro.version>1.10.0</avro.version>
<janino.version>3.1.2</janino.version>
<swagger.version>2.9.2</swagger.version>
<google-cloud-logging-logback.version>0.118.1-alpha</google-cloud-logging-logback.version>
<spring-cloud-stream-binder-kafka.version>3.0.6.RELEASE</spring-cloud-stream-binder-kafka.version>
</properties>
mvn versions:display-property-updates
[INFO] The following version properties are referencing the newest available version:
[INFO] ${avro.version} .............................................. 1.10.0
[INFO] ${spring-cloud-stream-schema.version} ................. 2.2.1.RELEASE
[INFO] ${janino.version} ............................................. 3.1.2
[INFO] The following version property updates are available:
[INFO] ${spring-cloud-gcp.version} .......... 1.2.3.RELEASE -> 1.2.5.RELEASE
[INFO] ${google-cloud-logging-logback.version} 0.118.1-alpha -> 0.118.2-alpha
[INFO] ${spring-cloud-stream-binder-kafka.version} 3.0.6.RELEASE -> 3.0.8.RELEASE
[INFO] ${confluent.version} ................................. 5.5.1 -> 6.0.0
[INFO] ${swagger.version} ................................... 2.9.2 -> 3.0.0
[INFO] ${spring-cloud.version} .................... Hoxton.SR6 -> Hoxton.SR8
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.572 s
[INFO] Finished at: 2020-10-06T09:35:08-07:00
[INFO] ------------------------------------------------------------------------
Another way to achieve this is by executing the command mvn versions:display-dependency-updates but the problem I face with this approach is that it also shows me updates for the nested dependencies which are not too useful for me.

You can use the Versions Maven Plugin[1] to generate reports in your Maven site to get a list of possible updates. With regard to Spring's irregularity, it appears to use the Mercury versioning system[2]. When configuring the Versions plugin, you can add a special rule for Spring stuff:
http://mojo.codehaus.org/versions-maven-plugin/
http://docs.codehaus.org/display/MAVEN/Mercury+Version+Ranges

I might be a bit late to join the party but a more clear way to get more readable html file or a xml file as report which can be taken for further automation using:
mvn versions:dependency-updates-report
This report plugin not just shows more comprehensive details on updates but also has options to update to latest versions. You can find the documentation for it to use various parameters.

You can use Maven Check, a command line tool, which is standalone unlike the Versions Maven Plugin. It also works with Gradle projects.
Output example:
2 build file(s) found, checking for artifact updates
my-gradle-project\build.gradle
[COMPILE ONLY] com.google.guava:guava 31.0-android -> 31.1-android
1 artifact update(s) available
my-maven-project\pom.xml
[DEPENDENCY] org.apache.commons:commons-lang3 3.10 -> 3.12.0
[BUILD PLUGIN] org.apache.maven.plugins:maven-compiler-plugin 3.10.0 -> 3.10.1
2 artifact update(s) available
2/2 build file(s) checked, 3 artifact update(s) available
Disclaimer: I am the author of Maven Check.

Maven error: "You don't have a SNAPSHOT project in the reactor projects list."

What on earth does this mean? Cant find any help via google.
> mvn release:prepare
[INFO] Scanning for projects...
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building Base 1.0.5
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-release-plugin:2.3.2:prepare (default-cli) # base ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.386s
[INFO] Finished at: Tue Oct 08 08:22:46 EST 2013
[INFO] Final Memory: 9M/81M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-release-plugin:2.3.2:prepare (default-cli) on project base: You don't have a SNAPSHOT project in the reactor projects list. -> [Help 1]

release:prepare command is supposed to prepare your snapshot project for the release. It sounds like you don't have such a snapshot project.
Here's the full details what it'll do: http://maven.apache.org/maven-release/maven-release-plugin/examples/prepare-release.html
If you're sure you should be releasing, you should be working on a maven module that has version ending with -SNAPSHOT.
Update: like noted by #khmarbaise in the comments, if your release has failed, you should do release:rollback to go back to previous state. Note though that it is not supported if you release through jenkins (jenkins issue), and it won't rollback the tags.

Don't needed manually edit pom.xml.
You can use "mvn versions:set" for batch update, something like this:
mvn versions:set -DnewVersion=1.0.3-SNAPSHOT

I've had the same error with Jenkins. In a previous release, Jenkins updated the version of the POM to a non-snapshot version, but the build failed before Jenkins could set the version to a -SNAPSHOT version again. Afterwards, making a release resulted in the error described above.
Fixing this is easy: just manually change the version of your app in pom.xml to a -SNAPSHOT version.

I know this is an old question but I had this issue recently and I found 2 solutions that others may find useful. I am using bamboo as my CI tool. The issue was that there was an error in the bamboo build leaving bamboo in an incorrect state. It had locally updated my project pom.xml with the new release version but had not checked this into SVN. The two solution that worked for me were:
Either
Delete the bamboo build-dir directory for the project and run the release again: rm -rf /opt/bamboo-home/xml-data/build-dir/PROJECT_NAME-RELEASE-JOB1
OR
Run the maven release from the command line using the following commands:
mvn release:prepare -DignoreSnapshots -Dresume=false
mvn release:perform

No need to update versions manually as that is time consuming, if version change is all you need, there is a different command that only updates the pom versions, just like updating them manually:
mvn versions:set -DgenerateBackupPoms=false -DnewVersion=1.0.XX-SNAPSHOT