Develop Reference

How to find the dependencies of a maven plugin goal

I'm trying to find out where the dependencies are coming from for a particular plugin goal. I know the dependencies exist because Maven downloaded them when I ran the goal for the first time. And they're not (directly) dependencies of my project, because I ran mvn clean install first, and these dependencies weren't downloaded then.
In this specific case, I'm trying to figure out what the dependencies are when I run mvn sonar:sonar, but I expect the answer will be general purpose. For instance, even though I've built this project a number of times, when I ran that goal Maven downloaded a bunch of new jars like maven-antrun-plugin.
Here are things I've tried:
mvn dependency:tree shows the dependencies for the project, but not for the plugin goal (it doesn't include anything related to SonarQube in the list).
mvn org.apache.maven.plugins:maven-help-plugin:3.2.0:effective-pom -Dverbose=true also doesn't include anything related to SonarQube.
mvn -X sonar:sonar prints out what looks like a dependency graph, but it's missing the jars that Maven downloaded the first time I ran the sonar:sonar goal.
mvn -X dependency:resolve-plugins seems to be meant to download the dependencies of plugins, but does not capture the sonar:sonar dependencies. If I clear out my Maven cache, run mvn dependency:resolve-plugins, and then run mvn sonar:sonar, Maven has to download jars.

Use your IDE to navigate to the POM of the plugin project and then look at the dependency tree.
Or do this manually by copying the plugin POM to your file system and running mvn dependency:tree.

The dependencies downloaded by maven are generally stored locally on the pc at the address C:\Users\yourUser/.m2 this regardless of your projects and so that you do not have to reload dependencies that you are already using in other projects.
I hope I have understood your question and that my answer is useful to you, greetings.

What is the equvalent of npm install in maven

i am new to java and have mainly used node.js for most of my projects. I have used npm and used the npm install function to download packages. In maven, is there a similar function that easily installs packages?

mvn dependency:resolve
Is worth take a look to mvn life cycles

There's also mvn dependency:go-offline to download the dependencies and prepare to run the rest of the tasks without any connection to the internet.
I was looking for a way to install maven dependencies during a CI job, while explicitly NOT compiling the code or running the tests.

Keep all the dependencies in your pom.xml(You can think of this as package.json). If you are using an IDE like eclipse it will automatically download the dependencies for you. If you want to download the dependencies from the command line run mvn install.
You can find the corresponding XML for dependencies here https://mvnrepository.com/

Maven doesn't have an install command. Before any task you run maven checks if the project was changed and downloads any new dependency you specified from Maven Central repository.
EDIT: Maven calls the resolver for most tasks you run.

Equivalents for mvn update and mvn install in gradle

I am new in gradle hence I have some questions about gradle. Before gradle I worked with maven and in maven there are some commands such as
mvn update
mvn clean install
With mvn update we download the dependency packages from internet and the other packages from the different projects.
With mvn install we create the jar, war, ear or ejb
so what are the equivalents for maven command in gradle?
mvn update ~= gradle ...
and
mvn clean install ~= gradle clean ...

Gradle will automatically fetch all required dependencies for you.
Long story short:
mvn update ~= ./gradlew build --refresh-dependencies
mvn clean install ~= ./gradlew clean build
TL;DR
To force Gradle to redownload dependencies you can execute (How can I force gradle to redownload dependencies?):
./gradlew build --refresh-dependencies
To assemble you project without executing tests (Gradle build without tests):
./gradlew assemble
To completely build you project with test execution:
./gradlew build
You can skip certain tasks by providing -x argument:
./gradlew build -x test

The equivalent to
mvn clean install
is
gradle install
what is provided by the maven plug-in of Gradle. Just add the following line to your build.gradle file:
apply plugin: 'maven'

This works for me.
./gradlew publishToMavenLocal

Here is the command:
./gradlew build

How do I build this java project with maven?

I honestly don't know anything about java, I'm just trying to build the latest version of this project to try and work around bugs in the version that is packaged by my OS. The project in question:
https://sourceforge.net/projects/tuxguitar/
I tried running mvn compile, mvn clean package, and mvn clean install but no jar file was produced in the source tree. The readme has no instructions for building. Any help would be greatly appreciated!
Thanks!

To produce jar you need at least package phase, you can get there by doing:
mvn clean package
(clean is to remove stale data, it is a good practice to use it always with maven) and you jar will be in target directory.

mvn complite just complite the project and no package.
answer : mvn clean package.this will clean,complite and package the project,after finished, you can found the package(jar or war) into the $PROJECT_HOME/target/ folder.

I usually run mvn clean install - which in addition will add the built jar into your local maven artifact repository.

specify pom.xml in mvn command and mix goals of other project

I have multiple questions.
Can I specify the pom.xml in mvn command?
Can I mix the goals of another project while executing mvn command on current project ?
Eg: mvn clean-otherproject comple-otherproject instal-otherproject compile-thisproject
I can do this with multiple mvn commands, but Can I do this in single maven command.

Just mvn --help would have answered the first question:
mvn -f otherPomFile.xml
No. You can simple execute the phases for the current project you are in. You can give multiple phases like
mvn clean install site site:deploy

For the first question, see khmarbaise's answer
If you want to build more than one maven project in one step, you must use modules.
In a multi-module project, if you call mvn install from the top project, all sub modules are built, unless you use the advanced reactor options (e.g. mvn install -pl util -am only builds the module 'util' and it's dependencies)