Demystifying Maven

Demystifying By Mike Desjardins

Topics Installation Shock and Awe: Comparison with ant Project Object Model (POM) Inheritance and Modules Dependencies Build Configuration Whirlwind Tour of Plugins Lifecycles Build Profiles Sometimes Maven Lets You Down

About Me Developed Software professionally for about 15 years, the last 5 with Java Independent Contractor/Consultant Live in Portland, Maine For the past several years, primary focus has been on web services Wireless Telecommunications Financial Services Online Music Website: http://mikedesjardins.us Twitter: @mdesjardins

Installation Requires JDK 1.4 Download Maven from http://maven.apache.org/ Unzip the archive Add the M2_HOME environment variable and point it to your installation. Make sure JAVA_HOME is set and java is in your PATH. Make sure $M2_HOME/bin is in your PATH.

Ant vs. Maven Best illustrated by Example We will create a new trivial Hibernate Application that reads rows in a database table (shown below) and outputs them to the console. greeting_id greeting_text 1 Hello 2 Bon jour 3 Buenos dias 4 Kon ni chi wa

Example – Source Code First, we will need a class to represent a greeting: @Entity public class Greeting { @Id @GeneratedValue (strategy=GenerationType. IDENTITY ) @Column (name= "greeting_id" ,nullable= false ,unique= true ) private Integer id ; @Column (name= "greeting_text" ) private String text ; @Column (name= "version" ) @Version private Integer version ; public Integer getId() { return this . id ; } public void setId(Integer id) { this . id = id; } public String getText() { return this . text ; } public void setText(String text) { this . text = text; } }

Example – Source Code Next, we will need a class with a static main method to actually do stuff...

Example – Source Code public class App { private static SessionFactory sessionFactory ; static { try { sessionFactory = new AnnotationConfiguration().configure().buildSessionFactory(); } catch (Throwable t) { System. out .println( "Something terrible has happened." ); t.printStackTrace(); } } public static SessionFactory getSessionFactory() { return App. sessionFactory ; } public void run() { System. out .println( "======================================================" ); Criteria c = App. getSessionFactory ().openSession().createCriteria(Greeting. class ); List<Greeting> greetings = c.list() ; for (Greeting greeting : greetings) { System. out .println(greeting.getId() + ": " + greeting.getText()); } System. out .println( "======================================================" ); } public static void main(String args[]) { App app = new App().run()); } }

Ant: Let's Get Started! First, let's create the directories for our project: Mac:~/_work$ mkdir demo-ant Mac:~/_work$ cd demo-ant Mac:~/_work/demo-ant$ mkdir src lib conf target Mac:~/_work/demo-ant$ cd src Mac:~/_work/demo-ant/src$ mkdir com Mac:~/_work/demo-ant/src$ cd com Mac:~/_work/demo-ant/src/com$ mkdir techmaine Mac:~/_work/demo-ant/src/com$ cd techmaine Mac:~/_work/demo-ant/src/com/techmaine$ mkdir antdemo Mac:~/_work/demo-ant/src/com/techmaine$

Ant: Let's Get Started! (If you’re more of a visual person)

Let's go get our jars! 1.) Visit the Hibernate Website, eventually find their download page…

Let's go get our jars! 2.) Download gigantic ZIP file ZZZZZZZZZ….

Let's go get our jars! 3.) Unpack the ZIP file 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/ 26428 09-10-08 12:21 hibernate-distribution-3.3.1.GA/lgpl.txt 1456 09-10-08 12:21 hibernate-distribution-3.3.1.GA/hibernate_logo.gif 152761 09-10-08 12:21 hibernate-distribution-3.3.1.GA/changelog.txt 2766130 09-10-08 12:27 hibernate-distribution-3.3.1.GA/hibernate3.jar 31493 09-10-08 12:22 hibernate-distribution-3.3.1.GA/hibernate-testing.jar 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/lib/ 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/lib/required/ 443432 06-13-08 12:09 hibernate-distribution-3.3.1.GA/lib/required/antlr-2.7.6.jar 559366 06-13-08 12:09 hibernate-distribution-3.3.1.GA/lib/required/commons-collections-3.1.jar 313898 06-13-08 12:09 hibernate-distribution-3.3.1.GA/lib/required/dom4j-1.6.1.jar 13236 06-13-08 12:09 hibernate-distribution-3.3.1.GA/lib/required/jta-1.1.jar 17384 08-19-08 19:40 hibernate-distribution-3.3.1.GA/lib/required/slf4j-api-1.5.2.jar 471005 06-13-08 12:10 hibernate-distribution-3.3.1.GA/lib/required/javassist-3.4.GA.jar 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/lib/optional/ 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/lib/optional/c3p0/ 608376 06-13-08 12:12 hibernate-distribution-3.3.1.GA/lib/optional/c3p0/c3p0-0.9.1.jar 0 09-10-08 12:27 hibernate-distribution-3.3.1.GA/lib/optional/proxool/ 475943 06-13-08 12:12 hibernate-distribution-3.3.1.GA/lib/optional/proxool/proxool-0.8.3.jar . . . . . . Holy Shnikeys! Do I really need all of this stuff?!?

Next Steps Copy the jar files to your lib directory Option 1: Copy Everything (Lazy) Option 2: Copy only what you need (Tedious) Create your build.xml file

Create the build.xml Start with an empty file <?xml version="1.0"?> <project name="antdemo" default="compile" basedir="."> </project> Step 1

Create the build.xml Create some variables build.xml  <property name="lib" value="lib"/> <property name="src" value="src"/> <property name="conf" value="conf"/> <property name="target" value="target"/> <property name="classes" value="${target}/classes"/> Step 2

Create the build.xml Tell ant about all of your libraries build.xml <fileset id="compile.libs" dir="${lib}"> <include name="antlr-2.7.6.jar"/> <include name="asm.jar"/> <include name="asm-attrs.jar"/> <include name="cglib-2.1.3.jar"/> <include name="commons-collections-3.2.jar"/> <include name="commons-lang-2.3.jar"/> <include name="commons-logging-1.0.4.jar"/> <include name="dom4j-1.6.1.jar"/> <include name="ejb3-persistence.jar"/> <include name="javassist.jar"/> <include name="jboss-archive-browsing.jar"/> <include name="jdbc2_0-stdext.jar"/> <include name="jta.jar"/> <include name="xml-apis.jar"/> <include name="xercesImpl-2.6.2.jar"/> <include name="hibernate3.jar"/> <include name="hibernate-annotations.jar"/> <include name="hibernate-commons-annotations.jar"/> <include name="hibernate-entitymanager.jar"/> </fileset> Step 3

Create the build.xml Tell ant about compiling build.xml <target name="init"> <tstamp/> <mkdir dir="${classes}"/> </target> <target name="compile" depends="init"> <mkdir dir="${basedir}/${classes}"/> <javac srcdir="${basedir}/${src}" destdir="${basedir}/${classes}" debug="yes" target="1.5"> <classpath> <fileset refid="compile.libs"/> </classpath> </javac> <copy file="${basedir}/${conf}/hibernate.cfg.xml" todir="${basedir}/${classes}"/> </target> <target name="clean"> <delete quiet="yes" dir="${basedir}/${target}"/> <mkdir dir="${basedir}/${target}"/> </target> Step 4

Create the build.xml Tell ant how to run the app build.xml <fileset id="runtime.libs" dir="${lib}"> <include name="postgresql-8.2-507.jdbc3.jar"/> </fileset> <target name="run" depends="compile"> <java classname="com.techmaine.antdemo.App"> <classpath> <fileset refid="compile.libs"/> <fileset refid="runtime.libs"/> <pathelement location="${basedir}/${classes}"/> </classpath> </java> </target> Step 5

Recap We downloaded jars and dependencies ourselves We told ant The name of the jar file that we needed (Hibernate) All the dependent jar file names Where the jar files were located That it needed to compile java files Where the java files were located Where it should put the class files Where it should put the Hibernate configuration file How to run the application Where the jar and class files were located (again, this time for runtime) build.xml is 75 lines, but who’s counting?

Maven Terminology With maven, you execute goals in plugins over the different phases of the build lifecycle , to generate artifacts . Examples of artifacts are jars, wars, and ears. These artifacts have an artifactId , a groupId , and a version . Together, these are called the artifact’s “ coordinates .” The artifacts stored in repositories . Artifacts are deployed to remote repositories and installed into local repositories. A POM (Project Object Model) describes a project.

Create a Project Directory Maven has a command for starting a project: mvn archetype:create \ -DgroupId=com.techmaine \ -DartifactId=demo-mvn \ -DpackageName=com.techmaine.mvndemo \ -Dversion=1.0 Step 1

Create a Project Directory mvn archetype :create \ -DgroupId=com.techmaine \ -DartifactId=demo-mvn \ -DpackageName=com.techmaine.mvndemo \ -Dversion=1.0 Plugin Name Step 1

Create a Project Directory mvn archetype: create \ -DgroupId=com.techmaine \ -DartifactId=demo-mvn \ -DpackageName=com.techmaine.mvndemo \ -Dversion=1.0 Plugin Name Goal Step 1

Create a Project Directory Voila ! Look what maven has done for you: Step 1

Set up the dependencies Open pom.xml. We need to tell maven that we have a dependency on Hibernate: <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>com.techmaine</groupId> <artifactId>demo-mvn</artifactId> <packaging>jar</packaging> <version>1.0</version> <name>demo-mvn</name> <url>http://maven.apache.org</url> <dependencies> <dependency> <groupId>junit</groupId> <artifactId>junit</artifactId> <version>3.8.1</version> <scope>test</scope> </dependency> </dependencies> </project> We’ll add the dependency here. Step 2

Set up the dependencies <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate-annotations</artifactId> <version>3.3.1.ga</version> </dependency> This is all we need to add: We don’t need to tell Maven about any of the jars on which Hibernate depends; Maven takes care of all of the transitive dependencies for us! Step 2

Set up the compiler <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>2.0.2</version> <configuration> <source>1.5</source> <target>1.5</target> </configuration> </plugin> </plugins> </build> Maven assumes a default source version of 1.3. We need to tell it if we want 1.5. Here’s a preview of plugin configuration: STUPIDITY ALERT! Step 3

Set up Hibernate Configuration Create a resources directory beneath the main (and, optionally, test) directory, and put the Hibernate configuration file there. Files in the resources directory get copied to the root of the classpath when packaging occurs as part of the resource:resource goal (more on that later) The resources directories are automatically created for many of the archetypes, but not for the quickstart archetype that we used. Step 4

Package Next, package everything up before we run it. To do this, invoke maven thusly: mvn package This is an alternate way to invoke maven. Instead of specifying a plugin and goal, you specify a phase (in this case, package is the phase). A phase is a sequenced set of goals. The package phase compiles the java classes and copies the resources Step 5

Execute Next, use the exec plugin to run our application: mvn exec:exec \ -DmainClass=com.techmaine.mvndemo.App Step 6

Recap We told maven That we were making a “quickstart” project. That we depended on Hibernate Annotations. That we needed Java 1.5 pom.xml was 35 lines (would have been 22 if maven defaulted to Java 1.5 instead of 1.3)

Recap – Why Maven is Cool We downloaded jars and dependencies ourselves We told ant The name of the jar file that we needed (Hibernate) All the dependent jar file names Where the jar files were located That it needed to compile java files Where the java files were located Where it should put the class files Where it should put the Hibernate configuration file How to run the application Where the jar and class files were located (again, this time for runtime) build.xml is 75 lines, but who’s counting? We told maven That we were making a “quickstart” project. That we depended on Hibernate Annotations. That we needed Java 1.5 pom.xml was 35 lines (would have been 22 if maven defaulted to Java 1.5 instead of 1.3)

What can Maven do? When you first download it, almost nothing! Run goals Run phases (collections of goals) Download Dependencies* Download Plugins But... from where? * Actually, dependency downloads are done by a plugin, too.

Configuring Maven Settings Files (settings.xml) In ~/.m2 (per-user settings) and in Maven’s install directory, under conf (per-system settings) Alternate location for repository Proxy Configuration Per-server authentication settings Mirrors Download policies, for plugins and repositories; snapshots and releases.

Configuring Maven Project Object Model (pom.xml) Inherited – individual projects inherit POM attributes from parent projects, and ultimately inherit from the “Super POM” The Super POM is in Maven’s installation directory, embedded in the uber jar. The Super POM defines, among lots of other things, the default locations for the plugin and jar repositories, which is http://repo1.maven.org/maven2

Repositories Local - in ~/.m2/repository Remote - e.g., http://repo1.maven.org/maven2 or another internal company repository (any directory reachable by sftp will do). Contains dependencies and plugins Can be managed by a “Repository Manager” like Nexus

The POM Describes the project, declaratively General Information - Project Coordinates (groupId, artifactId, Version) Build Settings – Configuration of the plugins Build Environment – We can configure different profiles that can be activated programatically POM Relationships – Dependencies on other projects

Anatomy of a POM File <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <packaging>jar</packaging> <version>1.0.0</version> <name>Super Duper Amazing Deluxe Project</name> <modules>  </modules> <parent>  </parent> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

General Information <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <modules>  </modules> <parent>  </parent> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project> Coordinates

Project Inheritance <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

Project Inheritance What is inherited? Identifiers (groupId, artifactId, one must be different) Dependencies Plugin, Report Lists Plugin Configurations Why Inherit? Don’t repeat yourself, e.g., several projects use the same version of log4j. Enforce plugin version across projects

Multimodule Projects <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

Multimodule Projects Not the same thing as POM inheritance! A multimodule project builds submodules, but rarely produces an artifact itself Directory structure mimics module layout (e.g., if B is a submodule of A, then B will be a subdirectory of A).

Multimodule Projects <packaging>pom<packaging> <modules> <module>ejb</module> <module>ear</module> </modules> Depends on the EJB artifact Creates EJB jar

Multimodule: Reactor When Maven encounters a multimodule project, it pulls all of the POMs into the “Reactor” The Reactor analyzes module inter-dependencies to ensure proper ordering. If no changes need to be made, the modules are executed in the order they are declared. Maven then runs the goals on each module in the order requested.

User-Defined Properties <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

User-Defined Properties User-Defined properties are like ant properties: <properties> <hibernate.version>3.3.0.ga</hibernate.version> </properties> ... <dependencies> <dependency> <groupId>org.hibernate</groupId> <artifactId>hibernate</artifact> <version>${hibernate.version}</version> </dependency> </dependencies> Example from Maven: The Definitive Guide, Sonatype, O’Reilly p.266

Other Properties Maven Properties, project.* ${project.version} Settings Properties, settings.* ${settings.interactiveMode} Environment Variables, env.* ${env.JAVA_HOME} Java System Properties ${java.version}, ${os.arch}, ${user.dir}

Dependencies <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

Dependencies Maven’s pièce de résistance <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>awesome-lib</artifactId> <version>1.3.5</version> <scope>compile</scope> <optional>false</optional> </dependency> </dependencies>

Dependencies <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>awesome-lib</artifactId> <version>1.3.5</version> <scope>compile</scope> <optional>false</optional> </dependency> </dependencies> groupId and artifactId: must be unique

Dependencies <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>awesome-lib</artifactId> <version>1.3.5</version> <scope>compile</scope> <optional>false</optional> </dependency> </dependencies> 1.3.5 - prefer version 1.3.5, newer version is acceptable to resolve conflicts (1.3.4,1.3.9) - Any version between 1.3.2 and 1.3.9, exclusive [1.3.4,1.3.9] - Any version between 1.3.2 and 1.3.9, inclusive [,1.3.9] - Any version up to, and including, 1.3.9 [1.3.5] - Only version 1.3.5, do not use a newer version .

Dependencies <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>awesome-lib</artifactId> <version>1.3.5</version> <scope>compile</scope> <optional>false</optional> </dependency> </dependencies> compile - default, packaged. Available on compile-time and runtime CLASSPATH. provided - you expect the JVM or app container to provide the library. Available on compile-time CLASSPATH. runtime - needed to run, but not compilation (e.g., a JDBC driver) test - only needed during test execution (e.g., JUnit)

Dependencies <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>awesome-lib</artifactId> <version>1.3.5</version> <scope>compile</scope> <optional>false</optional> </dependency> </dependencies> Prevents this dependency from being included as a transitive dependency if some other project depends on this project.

Transitive Dependencies A 1.0 B 1.0 C 1.0 E 1.0 D 1.0 Our project (Project “A”) depends on B and C. Project C depends on projects D and E. Thus, our project depends on B, C, D, and E, and Maven will fetch and use these artifacts appropriately.

Transitive Dependencies A 1.0 B 1.0 C 1.0 E 1.0 D 1.0 Now, let’s say project C has a dependency on project B, but requires version 1.1. If project A’s POM doesn’t explicitly require version 1.0 or earlier, then Maven will choose version 1.1. B 1.1

Transitive Dependencies A 1.0 B [1.0] C 1.0 E 1.0 D 1.0 Uh oh. Now Project A is saying that it must use version 1.0 of B, and only version 1.0, and project C needs version 1.1 of project B. B [1.1]

Dependency Exclusions One way to deal with conflicts is with exclusions <dependencies> <dependency> <groupId>com.techmaine</groupId> <artifactId>project-b</artifactId> <version>[1.0]</version> </dependency> <dependency> <groupId>com.techmaine</groupId> <artifactId>project-c</artifactId> <exclusions> <exclusion> <groupId>com.techmaine</groupId> <artifactId>project-b</artifactId> </exclusion> </exclusions> </dependency> </dependencies>

Dependency Management Parent POM Child POM The dependencyManagement element allows you to specify version numbers of dependencies in child POMs without making all children dependent on a particular library. <dependencyManagement> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring</artifactId> <version>2.5.5</version> </dependency> </dependencies> </dependencyManagement> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring</artifactId> </dependency> </dependencies>

SNAPSHOT Versions SNAPSHOT is a literal string appended to a version number, e.g., 1.2.3-SNAPSHOT Indicates that a version is “under development” Use if you need Maven to keep checking for the latest version Maven replaces SNAPSHOT with a UTC time stamp before putting it into the repository.

Build Configuration <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

Build Configuration The build section of the POM, broken down further: <project> ... <build> <filters> <filter>filter/my.properties</filter> </filters> <resources> ... </resources> <plugins> ... </plugins> </build> ... </project>

Build Configuration Filters <project> ... <build> <filters> <filter>filter/my.properties</filter> </filters> <resources> ... </resources> <plugins> ... </plugins> </build> ... </project> Path to a properties file (name=value). When the resources are processed during packaging, maven will substitute any ${name} strings with the corresponding value from the properties file.

Build Configuration Resources The resources:resources goal copies files from the resources directory to the output directory Can process using filters Default location src/main/resources Can be further configured: <resources> <resource> <directory>src/main/scripts</directory> <filtering>true</filtering> <targetPath>bin</targetPath> <includes> <include>run.bat</include> <include>run.sh</include> </includes> <resource> </resources>

Build Configuration Plugins All work in Maven is performed by plugins Like Dependencies, are Downloaded from a repository Because they are shared, you often benefit from the fact that someone else has already built a plugin for whatever function you may need

Plugin Configuration The plugin section of the POM has a configuration element where you can customize plugin behavior: <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-clean-plugin</artifactId> <version>2.2</version> <configuration>  </configuration> </plugin> </plugins> </build>

Plugin Configuration: Example Below, we have configured the clean plugin to delete files ending in .txt from the tmp directory <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-clean-plugin</artifactId> <version>2.2</version> <configuration> <filesets> <fileset> <directory>tmp</directory> <includes> <include>**/*.txt</include> </includes> <followSymlinks>false</followSymlinks> </fileset> </filesets> </configuration> </plugin> </plugins> </build>

Core Plugins clean - has only one goal, clean. Deletes the target directory, can be configured to delete other stuff compiler - compiles sources, uses javac compiler by default. Has a compile and testCompile goal. Can be configured to use any executable as the compiler deploy - uploads artifacts to a remote repository Maven Plugin Whirlwind Tour

Core Plugins, cont. install - installs the artifact into the local repository. install goal, install this project’s artifact install-file goal, install a specific file into local repo (good for third-party stuff) surefire - runs all of the unit tests in the test source directory, and generates reports. resources - copies resources to be packaged Maven Plugin Whirlwind Tour

Packaging Plugins ear , ejb , jar , war assembly - builds a binary distribution including runtime dependencies supports zip, tar.gz, tar.bz2, jar, dir, and war formats uses “assembly descriptors” to configure (although several pre-fab ones are available) one of the pre-fab descriptors builds executable jar files with all depenencies embedded Maven Plugin Whirlwind Tour

Utility Plugins archetype - builds skeleton of a working project for many different frameworks Wicket, Tapestry 5, JSF, JPA, tons of others help - even the help is a plugin! Use the describe goal to learn what a plugin can do, e.g., mvn help:describe -Dplugin=compiler scm - source control stuff Maven Plugin Whirlwind Tour

Build Lifecycle Usually, an artifact is built by executing a sequence of goals For example, to generate a WAR: Clean the build area Copy the resources Compile the code Copy the test resources Compile the test code Run the test Package the result

Maven’s Lifecycles Maven supports three standard lifecycles clean - as you might expect, starts us fresh default - the lifecycle that builds the code site - a lifecycle for building other related artifacts (e.g., reports and documentation)

Clean Lifecycle The Clean Lifecycle has three phases: pre-clean clean post-clean Only clean is “bound” by default, to the clean goal of the clean plugin. You can bind other tasks using executions.

Executions Let’s say you have a whizz-bang plugin named mp3 , and it has a goal named play that lets you play an arbitrary audio clip, and you’d like to play a clip during pre-clean: <plugin> <groupId>com.techmaine</groupId> <artifactId>mp3</artifactId> <version>1.0</version> <executions> <execution> <phase>pre-clean</phase> <goals> <goal>play</goal> </goals> <configuration> <audioClipFile>toilet-flush.mp3</audioClipFile> </configuration> </execution> </executions> </plugin>

Maven’s Default Lifecycle Maven models the software build process with the 21 step “default lifecycle” validate generate-test-sources package generate-sources process-test-sources pre-integration-test process-sources generate-test-resources integration-test generate-resources process-test-resources post-integration-test process-resources test-compile verify compile test install process-classes prepare-package deploy

Package-Specific Lifecycles Maven automatically binds goals to the phases on the previous slide based on the packaging type. E.g., for projects that package WARs: Lifecycle Phase Goal process-resources resources:resources compile compiler:compile process-test-resources resources:testResources test-compile compiler:testCompile test surefire:test package war:war install install:install deploy deploy:deploy

Build Profiles <project xmlns= http://maven.apache.org/POM/4.0.0 > <modelVersion>4.0.0</modelVersion> <name>Super Duper Amazing Deluxe Project</name> <packaging>jar</packaging> <groupId>com.techmaine</groupId> <artifactId>superduper</artifact> <version>1.0.0</version> <parent>  </parent> <modules>  </modules> <properties>  </properties> <dependencies>  </dependencies> <build>  <plugins>  </plugins> </build> <profiles>  </profiles> </project>

Profiles: Customized Builds Sometimes our artifacts need to be tweaked for different “customers” The Development version has different logging or database configuration than QA or Production There might be slight differences based on target OS or JDK version

How to declare a profile In the POM itself, in an external profiles.xml file, or even in settings.xml <project> ... <profiles> <profile> <id>appserverConfig-dev</id> <properties> <appserver.home>/path/to/dev/appserver</appserver.home> </properties> </profile> <profile> <id>appserverConfig-dev-2</id> <properties> <appserver.home>/path/to/another/dev/appserver2</appserver.home> </properties> </profile> </profiles> ... </project>

Build Configuration in a Profile You can even configure plugins based on a profile: <project> ... <profiles> <profile> <id>production</id> <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <configuration> <debug>false</debug> <optimize>true</optimize> </configuration> </plugin> </plugins> <appserver.home>/path/to/dev/appserver</appserver.home> </build> </profile> ... Example from Maven: The Definitive Guide, Sonatype, O’Reilly p.200

Activating a Profile On the command-line: mvn package -Pmyprofile1,myprofile2 In your settings.xml file: <settings> ... <activeProfiles> <activeProfile>dev</activeProfile> </activeProfiles> ... </settings> Activation elements

Activation Elements <project> … <profiles> <profile> <id>dev</id> <activation> <activeByDefault>false</activeByDefault> <jdk>1.5</jdk> <os> <name>Windows XP</name> <family>Windows</famliy> <arch>x86</arch> <version>5.1.2600</version> </os> <property> <name>mavenVersion</name> <value>2.0.9</value> </property> <file> <exists>file2.properties</exists> <missing>file1.properties</missing> </file> </activation> … </profile> </profiles> </project> Example from Maven: The Definitive Guide, Sonatype, O’Reilly p.204-205

Sometimes Maven Sucks … returns “about 128,000” results

Common Criticisms Poor Documentation - Lots of Maven’s online documentation is automatically generated and is generally pretty horrible Simple things are sometimes counterintuitive with Maven - E.g., copying a file Maven adds to the number of places you need to look when something breaks - both your source repository, and the maven repository Everything breaks if someone changes an artifactId or groupId Doesn’t work well if your network connectivity is unreliable or unavailable Gets tangled and confused if one of your transitive dependencies isn’t available in a maven repository

Demystifying Maven

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