Ways to make maven build faster?

I have a multi module java project. Maven takes almost around 40 secs to build it. I have tried maven with multi threaded builds too by specifying -T and -C args for no of threads and cores to be used. But I haven't seen any significant improvement in wall time of my builds.
I am using maven 3.2.3 and sometimes I need to build my project very frequently.
I know that clean goal take a lot of time but I can not omit it.
Suggestions please....

EDIT:
Note: In my case clean is not taking much time. It finishes in 1 sec. install is taking rest of the time.

Note: First thing is AFAIK, No other in built options available in maven apart from the all answers here.

---

Running maven build with Multiple threads works for me to speed up the builds. For example :

mvn clean install -T100

> where -T is for specifying how many threads you want based on your > hardware.

###Below are the variants from wiki

> Maven 3.x has the capability to perform parallel builds. The command > is as follows: > > - mvn -T 4 clean install Builds with 4 threads > - mvn -T 1C clean install 1 thread per cpu core
> - mvn -T 1.5C clean install 1.5 thread per cpu core

###How Execution is evaluated(See Parallel builds in Maven 3)?

Each node in the graph represents a module in a multi-module build, the "levels" simply indicate the distance to the first module in the internal reactor dependency graph. Maven calculates this graph based on declared inter-module dependencies for a multi-module build. Note that the parent maven project is also a dependency, which explains why there is a single node on top of most project graphs. Dependencies outside the reactor do not influence this graph.

Finally if you want to skip test execution you can also use -DskipTests as well.

Caution : Some of your plugins may not be compatible for multithreaded builder, it may work. but it will give below warning message. you may need to see plugin documentation for multithreading support.

[WARNING] *****************************************************************                                                                                                                                 
[WARNING] * Your build is requesting parallel execution, but project      *                                                                                                                                 
[WARNING] * contains the following plugin(s) that have goals not marked   *                                                                                                                                 
[WARNING] * as @threadSafe to support parallel building.                  *                                                                                                                                 
[WARNING] * While this /may/ work fine, please look for plugin updates    *                                                                                                                                 
[WARNING] * and/or request plugins be made thread-safe.                   *                                                                                                                                 
[WARNING] * If reporting an issue, report it against the plugin in        *                                                                                                                                 
[WARNING] * question, not against maven-core                              *                                                                                                                                 
[WARNING] *****************************************************************                                                                                                                                 
[WARNING] The following plugins are not marked @threadSafe in test-project:                                                                                                                          
[WARNING] de.dentrassi.maven:rpm:0.9.2                                                                                                                                                                      
[WARNING] Enable debug to see more precisely which goals are not marked @threadSafe.                                                                                                                        
[WARNING] *****************************************************************    

On my actual project :

1. mvn clean install [INFO] Total time: 01:05 h
2. mvn clean install -DskipTests [INFO] Total time: 18:35 min
3. mvn clean install -Dmaven.test.skip -DskipTests [INFO] Total time: 10:58 min
4. mvn -T 1C clean install -Dmaven.test.skip -DskipTests [INFO] Total time: 04:00 min
5. We can also skip the javadoc to be generated as Archmed commented by adding -Dmaven.javadoc.skip=true mvn -T 1C clean install -Dmaven.test.skip -DskipTests -Dmaven.javadoc.skip=true
6. Don't use * imports, on IntelliJ, choose > Analyze > Run inspection by name > * imports , to find all * imports and correct it.
7. Remove all unused imports in your project > on Intellij > Analyze > Run inspection by name > unused imports
8. Remove all unused code (classes, variable, field, parameter, etc..), on Intellij : Analyze > run inspection by name > unused declaration.
9. Upgrade to last JAVA VERSION
10. I have found that the task mvn clean, is taking 2 minutes to clean the TARGET folder before building. I did create a new task called quickclean, and I am using it instead of clean, this way mvn -T 1C quickclean install -Dmaven.test.skip -DskipTests . This new task quickclean is only renaming the build folder from TARGET to TARGET-yyyy-MM-dd-HH-mm(what is VERY FAST). So now, every time you make a new mvn quickclean install..., you have a folder with the time of the build. The inconvenient, it's that this may take a lot of space on the hard disk, so you have to clean all these directories sometimes. So for that I have created another task called: trashclean, to put all this folder to trash. I am running this tasks maybe on time per week. or month, depending on my work mvn trashclean.

Here is what you need to add to your pom.xml if you want to use this concept

<properties>
	<timestamp>${maven.build.timestamp}</timestamp>
    <maven.build.timestamp.format>yyyy-MM-dd-HH-mm</maven.build.timestamp.format>
    <trashdir>trash/target-${maven.build.timestamp}</trashdir>
</properties>

	<profile>
        <id>quickclean</id>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-antrun-plugin</artifactId>
                    <executions>
                        <execution>
                            <id>rename_target</id>
                            <phase>pre-clean</phase>
                            <goals>
                                <goal>run</goal>
                            </goals>
                            <configuration>
                                <tasks>
                                    <move todir="${trashdir}" failonerror="false">
                                        <fileset dir="target/"/>
                                    </move>
                                </tasks>
                            </configuration>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>
    </profile>
    <profile>
        <id>trashclean</id>
        <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-antrun-plugin</artifactId>
                    <executions>
                        <execution>
                            <id>clean_trash</id>
                            <phase>clean</phase>
                            <goals>
                                <goal>run</goal>
                            </goals>
                            <configuration>
                                <tasks>
                                    <delete dir="trash/" failonerror="false"/>
                                </tasks>
                            </configuration>
                        </execution>
                    </executions>
                </plugin>
            </plugins>
        </build>
    </profile>
	

You can optimize the build by using of some small-2 trick like

1. If you have written Junit Test and dont want to run test case every time you can use -DskipTests=true
2. Locally Install Nexus or Repositories
3. You can adjust memory configurations to optimum for eg: add this line to mvn.bat set MAVEN_OPTS=-Xmx512m -XX:MaxPermSize=256m

For more information you can check How to Speed Your Maven build

If using commandline you can check how many cores your machine has and use all of them, if you also want to skip your tests, you can add -DskipTests For example, I have 8 core processor:

mvn -T 8C clean install -DskipTests

You can do a hacky way if you have some extra RAM as I do, and you don't need SSD, because it's sensitive for SSD to do a lot of read-writes. Even if you disable +a bit (MacOS - I don't remember if Win have similar issue). But

1. create RAM drive (number of ways depends on your OS) and mount it to /Users/Username/volatile folder

2. locate maven-module-builder-X.X.X.jar in MVN_HOME/lib

3. in JAR modify file org/apache/maven/model/pom-4.0.0.xml by modifying

<build><directory>/Users/Username/volatile/${project.groupId}/${project.artifactId}/${project.version}/target

4. From now on all project compilations will be done in memory. And it's a difference even in comparison with SSD.

Yes, its hack and some maven plugins can stop working BTW.

Apart from parallel run which many of the folks have already mentioned, try these maven options which would speed up build -XX:+TieredCompilation -XX:TieredStopAtLevel=1

Low-Level speed using Ramdisk (Windows)

My additional trick is using a ramdisk

1. Create a Ramdisk of 2GB (in example D:)
2. Install IDE, Maven, JDK and the .m2/repository to that Ramdisk (D:/m2/).
3. Edit the Maven's D:/maven/conf/settings.xml to use that Ramdisked repo (<localRepository>D:/m2</localRepository>)
4. Put the project into the ramdisk.
5. Run the project having its temp-folder in the Ramdisk.

On my machine I turned

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 14.954 s (Wall Clock)
[INFO] Finished at: 2021-02-17T13:07:51+01:00
[INFO] Final Memory: 55M/642M
[INFO] ------------------------------------------------------------------------

Into

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  6.805 s (Wall Clock)
[INFO] Finished at: 2021-11-11T10:48:14Z
[INFO] ------------------------------------------------------------------------

Both results are high-end (-DskipTests -T 12)

Warning: Do not forget to persist the ramdisk before shutdown or your work is lost.

Look at this beast: