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Maven Summary

· 3 min read
Shixu

What is Maven​

TL;DR

Lifecycles, phases and (plugin) goals​

Concepts​

Similar to gitlab pipelines,stages and jobs

  • Three built-in build lifecycles: default , clean and site

  • When we run a phase – all goals bound to this phase are executed in order. This won't only execute the specified phase but all the preceding phases as well

E.g. mvn clean install

  • A goal can bound to one or more build phases. A build phase can also have zero or more goals bound to it

default lifecycle bindings

  • A goal not bound to any build phase could be executed outside of the build lifecycle by direct invocation

E.g. mvn dependency:tree

Look up phases and goals​

Use mvn fr.jcgay.maven.plugins:buildplan-maven-plugin:list to list phases and goals in default lifecycle

Direct/Transitive dependency​

A -> B -> C , B, C is A's dependency, B is A's direct dependency, C is A's transitive dependency

Dependency conflict​

The different versions of same dependency are all needed by others

Dependency mediation​

  • Nearest definition

A -> B -> C -> D 2.0 and A -> E -> D 1.0 result will be D 1.0

  • First declaration
// A.xml
<dependecy>B</dependency>
<dependecy>C</dependency>

A -> B -> D 2.0 and A -> C -> D 1.0 result will be D 2.0

Solution​

  • According dependency mediation if have compatible versions
  • Use shade plugin if have not uncompatible versions

Best practice​

  • Although transitive dependencies can implicitly include desired dependencies, it is a good practice to explicitly specify the dependencies your source code uses directly. This best practice proves its value especially when the dependencies of your project change their dependencies

  • Use a dependencyManagement section in a parent pom.xml to avoid duplicating dependency information in child projects

  • The phases named with hyphenated-words (pre-, post-, or process-*) are not usually directly called from the command line. These phases sequence the build, producing intermediate results that are not useful outside the build. In the case of invoking integration-test, the environment may be left in a hanging state

Commonly used​

Commands​

  • Help making best practice more achievable: mvn dependency:analyze

  • Run ut singly: mvn -DfailIfNoTests=false -pl product.profile-service -Dtest=CheckSetHotelValidatorTest -am test

  • Download artifact: mvn dependency:get -DremoteRepositories=http://repo1.maven.org/maven2/ -DgroupId=com.google.code.gson -DartifactId=gson -Dversion=2.8.8

Refs​