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Maven Tips... and Tricks

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Maven, one of the central actors in the Java World, resposible for managing the building life-cycles of many projects, is full of little features, that sometimes we forget to explore.

Let us go straight away and take a look at some very useful Maven features that will make your builds shine.

From where it stopped


Sometimes it is needed to build a bunch of projects all together, artifact-a, artifact-b and so on. What do we usually do when one of them fail? Build it all again!

But not anymore:

mvn -rf yourprojects-module clean install
view raw gistfile1.java hosted with ❤ by GitHub

By using this option you can run the build from the project that failed.

Two out of ten

Ok, suppose you have 10 projects, and you only want to build 2 of them, how would you do?

The option -pl will do the job

mvn -pl artifact-a,artifact-b clean install
view raw gistfile1.txt hosted with ❤ by GitHub

Multi-threaded Build

If in the machine you run the build you have many Cores, tou can take advantage of them by using the following option(it means 2 Threads per Core):
mvn clean install -T2C
view raw gistfile1.txt hosted with ❤ by GitHub

It is also possible to define 3 Threads per Core(T3C)

Skip your Tests when you want to

With a lot of tests to perform your complete phases might really take too long and sometimes you only want to test a new or small functionality, you might skip the Tests by using the DskipTests

mvn clean install -DskipTests
view raw gistfile1.txt hosted with ❤ by GitHub

Running Offline

Wanna run your builds without maven connecting to repositories, checking for updates? You asked you got it!
mvn clean install -o
view raw gistfile1.txt hosted with ❤ by GitHub

When running with the offline option enabled, Maven will not attempt to connect to a remote repository to retrieve artifacts.
Bonus - Deal with failures

The following options control how Maven reacts to a build failure in the middle of a multi-module project build: 
-fae, --fail-at-end
view raw gistfile1.txt hosted with ❤ by GitHub

Only fail the build afterwards; allow all non-impacted builds to continue

-ff, --fail-fast
view raw gistfile1.txt hosted with ❤ by GitHub

Stop at first failure in reactorized builds

-fn, --fail-never
view raw mvn-fail-never.mvn hosted with ❤ by GitHub

NEVER fail the build, regardless of project result

The -fn and -fae options are useful options for multi-module builds that are running within a continuous integration tool like Hudson. The -ff option is very useful for developers running interactive builds who want to have rapid feedback during the development cycle.

That's all for today, hope your builds will never be the same...

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