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maven: execute without actually building anything

I have a project with finalised version in pom files , lets say 12.3.45 .
I have built the code for this version some time ago already, all the built jars are in the local maven repo.
Then at some point I have run mvn clean, so all the target folders are being removed.
And now I want to execute some code, as quickly as possible, using mvn exec:java. Preferably without building anything, because why not? all the jars at some point were already built, and I know there were no code changes after that. How can I force maven to execute the code as fast as possible , not recompile anything, and just reuse the jars from the local repo?
Thanks.

If your artifacts are in a local or remote repository you can use them as dependencies.
You can use exec-maven-plugin's options includeProjectDependencies or includePluginDependencies to use them in java execution
https://www.mojohaus.org/exec-maven-plugin/java-mojo.html#includePluginDependencies. includeProjectDependencies option is enabled (true) by default.
You can execute exec-maven-plugin without building anything with mvn exec:java command
Instructions:
To run exec-maven-plugin you would need a main class to run. I assume you have one in your project. If you don't - you need to make a separate project with a main class.
Create a blank maven project.
In the project add exec-maven-plugin configuration. Set the mainClass
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<goals>
<goal>java</goal>
</goals>
<configuration>
<mainClass>pack.App</mainClass>
</configuration>
</plugin>
</plugins>
</build>
Include you artifacts as dependencies to the project
<dependencies>
<dependency>
<groupId>my.group</groupId>
<artifactId>myartifact</artifactId>
<version>12.3.45</version>
</dependency>
</dependencies>
Run mvn exec:java to execute com.my.package.MyMainClass main class from my.group.myartifact artifact
Edits:
includeProjectDependencies option is enabled (true) by default

Java: how to set java path for Windows and MAC

I have Java maven project with TestNG
Please see this pom.xml:
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.0</version>
<configuration>
<fork>true</fork>
<executable>C:\Program Files\Java\jdk1.8.0_181\bin\javac.exe</executable>
</configuration>
</plugin>
So inside Windows when I want to run this project from command line I just navigate into this pom.xml folder and then:
mvn clean test
And this will start all my tests.
Now inside this pom.xml i have my javac.exe path so in order to run this project in MAC what I need to add/ change? (I want it to support both OS)

The best practice would probably be to rely on the standard JAVA_HOME environment variable:
<executable>${env.JAVA_HOME}/bin/java</executable>

Can't run java code when using package [duplicate]

Is there a Maven "phase" or "goal" to simply execute the main method of a Java class? I have a project that I'd like to test manually by simply doing something like "mvn run".

See the exec maven plugin. You can run Java classes using:
mvn exec:java -Dexec.mainClass="com.example.Main" [-Dexec.args="argument1"] ...
The invocation can be as simple as mvn exec:java if the plugin configuration is in your pom.xml. The plugin site on Mojohaus has a more detailed example.
<project>
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<configuration>
<mainClass>com.example.Main</mainClass>
<arguments>
<argument>argument1</argument>
</arguments>
</configuration>
</plugin>
</plugins>
</build>
</project>

1. Edit POM.xml
Add the following property in pom.xml. Make sure you use the fully qualified class name (i.e. with package name) which contains the main method:
<properties>
<exec.mainClass>fully-qualified-class-name</exec.mainClass>
</properties>
2. Run Command
Now from the terminal, trigger the following command:
mvn clean compile exec:java
NOTE You can pass further arguments via -Dexec.args="xxx" flag.

The above mentioned answers are correct but I am simplifying it for noobs like me.Go to your project's pom file. Add a new property exec.mainClass and give its value as the class which contains your main method. For me it was DriverClass in mainpkg. Change it as per your project.
Having done this navigate to the folder that contains your project's pom.xml and run this on the command prompt mvn exec:java. This should call the main method.

No need to add new plugin in pom.xml. Just run this command
mvn org.codehaus.mojo:exec-maven-plugin:1.5.0:java -Dexec.mainClass="com.example.Main" | grep -Ev '(^\[|Download\w+:)'
See the maven exec plugin for more usage.

Give the Exec Maven plugin a try

clean package exec:java -P Class_Containing_Main_Method command is also an option if you have only one Main method(PSVM) in the project, with the following Maven Setup.
Don't forget to mention the class in the <properties></properties> section of pom.xml :
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
<java.main.class>com.test.service.MainTester</java.main.class>
</properties>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<configuration>
<mainClass>${java.main.class}</mainClass>
</configuration>
</plugin>
STS Run Configuration along with above Maven Setup:

Run a single java package on eclipse using maven

I have multiple java packages in my java project. Is it possible to run a single package on eclipse using maven. I want to do it with the project level pom. I dont want to create POMs for every package.

Based on your comment, not sure if this is what you are looking for but I use a configuration variable to run test cases for a particular package. You have to add a plugin to the POM to achieve this.
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-surefire-plugin</artifactId>
<version>2.7.2</version>
<configuration>
<includes>
<include>**/${testGroup}/*Test.java</include>
</includes>
</configuration>
</plugin>
</plugins>
</build>
Now if you want to run the test cases for lets say package org/myPackage you would use a command like this.
mvn test -DtestGroup=org/myPackage

Error in Maven building?

After i wrote
mvn -f pom.xml compile exec:java -Dexec.classpathScope=Compile-Dexec.main Class=storm.starter.WordCountTopology
and found this !!
[INFO] One or more required plugin parameters are invalid/missing for
'exec:java'
[0] Inside the definition for plugin 'exec-maven-plugin' specify the
following:
... VALUE
-OR-
on the command line, specify: '-Dstorm.topology=VALUE

If you link your pom.xml then this would be easier. I'm guessing you're using Storm. Have you written your own topologyClass? From the documentation:
topologyClass
The class name of the topology driver (e.g. "com.foo.bar.MyTopology")
Command line override: -Dmaven.storm.topology=
The documentation also gives you the code for your pom but you might want to add exec-maven-plugin to your pom.xml like so:
<build>
<plugins>
<plugin>
<groupId>org.codehaus.mojo</groupId>
<artifactId>exec-maven-plugin</artifactId>
<version>1.2.1</version>
<configuration>
<mainClass>com.domain.yourApp</mainClass>
</configuration>
</plugin>
</plugins>
</build>
One thing to note: you need to alter mainClass to match the class in your project that contains the main method you want to execute.
Then you can just run mvn exec:java.