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Tutorials

Example-driven introduction to Maven, “Maven by Example”: http://books.sonatype.com/mvnex-book/reference/public-book.html
Reference book: http://books.sonatype.com/mvnref-book/reference/
Conceptual model: http://warren.chinalle.com/wp-content/uploads/2011/07/maven-concepts1.png

Using Java 1.5+

If you use Maven with its default settings, chances are that you will get an error message like these:

[...] not supported in -source 1.3
[...] not supported in -source 1.5

To use Java 1.7, add the following element to the pom.xml file:

<properties>
	<maven.compiler.source>1.7</maven.compiler.source>
	<maven.compiler.target>1.7</maven.compiler.target>
</properties>

To use Java 1.8, add the following element to the pom.xml file:

<properties>
	<maven.compiler.source>1.8</maven.compiler.source>
	<maven.compiler.target>1.8</maven.compiler.target>
</properties>

In you develop in Eclipse and use the m2e plug-in, you can update the project’s .classpath file by right clicking the project and choosing Maven | Update Project….

Encoding

<properties>
	<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>

Specify the main class

Add the following:

<build>
	<plugins>
		<plugin>
			<groupId>org.apache.maven.plugins</groupId>
			<artifactId>maven-jar-plugin</artifactId>
			<version>2.4</version>
			<configuration>
				<archive>
					<manifest>
						<addClasspath>true</addClasspath>
						<classpathPrefix>lib/</classpathPrefix>
						<mainClass>fully.qualified.name.of.main</mainClass>
						<useUniqueVersions>false</useUniqueVersions>
					</manifest>
				</archive>
			</configuration>
		</plugin>
	</plugins>
</build>

The following part adds the lib directory to the classpath:

<addClasspath>true</addClasspath>
<classpathPrefix>lib/</classpathPrefix>

If you intend to use dependencies (and you do, that’s the main advantage of Maven), you have to copy them to the lib directory. To do so, add the following to the <plugins> element:

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-dependency-plugin</artifactId>
        <version>2.9</version>
	<executions>
		<execution>
			<id>copy-dependencies</id>
			<phase>package</phase>
			<goals>
				<goal>copy-dependencies</goal>
			</goals>
			<configuration>
				<outputDirectory>${project.build.directory}/lib</outputDirectory>
				<overWriteReleases>false</overWriteReleases>
				<overWriteSnapshots>false</overWriteSnapshots>
				<overWriteIfNewer>true</overWriteIfNewer>
			</configuration>
		</execution>
	</executions>
</plugin>

Building Xtend code

First, you should start by creating an Xtend archetype: https://www.eclipse.org/xtend/download.html#MavenSupport

If the Tycho compiler fails with the following error after the xtend maven builder completes successfully:

[ERROR] Failed to execute goal org.eclipse.tycho:tycho-compiler-plugin:0.18.1:compile (default-compile) on project X: Compilation failure: Compilation failure:
[ERROR] MyClass.java:[X,0]
[ERROR] MyXtendClass _var = new MyXtendClass();
[ERROR] ^^^^^^^^^^^^
[ERROR] MyXtendClass cannot be resolved to a type

Check the following:

The character encoding is correct (UTF-8), and opening the generated Java code in xtend-gen seems okay.
The xtend-gen/ directory is added to the list of source folders in build.properties.
This is normally a warning, but sometimes Eclipse does not display it correctly.
Tycho looks for sources based on this configuration. Hence, as a general rule of thumb, warnings in the build.properties file should be treated as an error.

Unexpected end of ZLIB input stream or error in opening zip file

[ERROR] Internal error: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: 
Exception parsing OSGi MANIFEST /home/szarnyasg/.m2/repository/p2/osgi/bundle/org.eclipse.core.resources/3.8.1.v20121114-124432/org.eclipse.core.resources-3.8.1.v20121114-124432.jar: 
error in opening zip file -> [Help 1]
org.apache.maven.InternalErrorException: Internal error: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: Exception parsing OSGi MANIFEST /home/szarnyasg/.m2/repository/p2/osgi/bundle/org.eclipse.core.resources/3.8.1.v20121114-124432/org.eclipse.core.resources-3.8.1.v20121114-124432.jar: error in opening zip file
	at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:168)
        [...]
	at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:352)
Caused by: org.eclipse.tycho.core.osgitools.OsgiManifestParserException: Exception parsing OSGi MANIFEST /home/szarnyasg/.m2/repository/p2/osgi/bundle/org.eclipse.core.resources/3.8.1.v20121114-124432/org.eclipse.core.resources-3.8.1.v20121114-124432.jar: error in opening zip file
	at org.eclipse.tycho.core.osgitools.DefaultBundleReader.doLoadManifest(DefaultBundleReader.java:74)
        [...]
	at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
	... 11 more
Caused by: java.util.zip.ZipException: error in opening zip file
	at java.util.zip.ZipFile.open(Native Method)
        [...]
	at org.eclipse.tycho.core.osgitools.DefaultBundleReader.doLoadManifest(DefaultBundleReader.java:67)
	... 21 more

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-shade-plugin:2.0:shade (make-shade) on project [...]: 
Error creating shaded jar: Unexpected end of ZLIB input stream -> [Help 1]
[...]
Caused by: java.io.EOFException: Unexpected end of ZLIB input stream
    at java.util.zip.ZipFile$ZipFileInflaterInputStream.fill(ZipFile.java:411)
    at java.util.zip.InflaterInputStream.read(InflaterInputStream.java:158)
    at java.io.FilterInputStream.read(FilterInputStream.java:107)
    at org.codehaus.plexus.util.IOUtil.copy(IOUtil.java:188)
    at org.codehaus.plexus.util.IOUtil.copy(IOUtil.java:174)
    at org.apache.maven.plugins.shade.DefaultShader.addRemappedClass(DefaultShader.java:259)
    at org.apache.maven.plugins.shade.DefaultShader.shade(DefaultShader.java:151)
    at org.apache.maven.plugins.shade.mojo.ShadeMojo.execute(ShadeMojo.java:484)
    ... 21 more

Possible cause: some files were downloaded with errors. Deleting the affected files or the whole local repository (the ~/.m2 directory) solves the problem.

Attaching the source to the file

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-source-plugin</artifactId>
        <version>2.4</version>
	<executions>
		<execution>
			<id>attach-sources</id>
			<goals>
				<goal>jar</goal>
			</goals>
		</execution>
	</executions>
</plugin>

Generating Eclipse plug-ins

The org.apache.maven.plugins:maven-source-plugin does not work the org.eclipse.tycho:tycho-maven-plugin: it results in No sources in project. Archive not created. and No product definitions found. Nothing to do. erros. Instead of the maven-source-plugin, use the following configuration:

<plugin>
	<groupId>org.eclipse.tycho</groupId>
	<artifactId>tycho-maven-plugin</artifactId>
	<version>${tycho.version}</version>
	<extensions>true</extensions>
</plugin>
<plugin>
	<groupId>org.eclipse.tycho</groupId>
	<artifactId>tycho-source-plugin</artifactId>
	<version>${tycho.version}</version>
	<executions>
		<execution>
			<id>plugin-source</id>
			<goals>
				<goal>plugin-source</goal>
			</goals>
		</execution>
	</executions>
</plugin>

The build runs but the program throws a NoClassDefFoundError

Source: http://stackoverflow.com/questions/13090487/how-do-i-correctly-use-snapshots-dependencies-with-ears-and-ejbs

You may get a NoClassDefFoundError caused by a ClassDefNotFoundError for classes in Maven artifact with a SNAPSHOT version. First, check the MANIFEST.MF file in the generated JAR file. In this case, it contains the following reference: lib/org.eclipselabs.emfjson-0.7.0-20140221.135604-5.jar. However, the file in the lib directory is actually called org.eclipselabs.emfjson-0.7.0-SNAPSHOT.jar. To resolve this, add the <useUniqueVersions>false</useUniqueVersions> to the configuration of the maven-jar-plugin:

<plugin>
	<groupId>org.apache.maven.plugins</groupId>
	<artifactId>maven-jar-plugin</artifactId>
	<version>2.4</version>
	<configuration>
		<archive>
			<manifest>
				<addClasspath>true</addClasspath>
				<classpathPrefix>lib/</classpathPrefix>
				<mainClass>[...]</mainClass>
				<useUniqueVersions>false</useUniqueVersions>
			</manifest>
		</archive>
	</configuration>
</plugin>

Installing JARs to the local repository

http://maven.apache.org/guides/mini/guide-3rd-party-jars-local.html

An example:

Installing the plain-java-project.jar:

mvn install:install-file -Dfile=plain-java-project.jar -DgroupId=plain-java-project -DartifactId=plain-java-project -Dversion=1.0-SNAPSHOT -Dpackaging=jar

Add the following dependency:

<dependency>
    <groupId>plain-java-project</groupId>
    <artifactId>plain-java-project</artifactId>
    <version>1.0-SNAPSHOT</version>
</dependency>

Modular Maven projects

Bash snippets to modular Maven project:

rm -rf trainbenchmark
mvn archetype:generate \
  -B \
  -DarchetypeGroupId=org.codehaus.mojo.archetypes \
  -DarchetypeArtifactId=pom-root \
  -DarchetypeVersion=1.1 \
  -DgroupId=hu.bme.mit.trainbenchmark \
  -DartifactId=trainbenchmark \
  -Dpackage=hu.bme.mit.trainbenchmark \
  -Dversion=1.0-SNAPSHOT

cd trainbenchmark/
mvn archetype:create -DgroupId=hu.bme.mit.trainbenchmark -DartifactId=train1
mvn archetype:create -DgroupId=hu.bme.mit.trainbenchmark -DartifactId=train2
mvn clean install

Difference between aggregator & parent

Running tests

Maven only runs the tests from classes whose name ends with Test.

http://stackoverflow.com/a/174670/90874

Class file is broken

[ERROR] /home/szarnyasg/git/incqueryd/hu.bme.mit.incqueryd.runtime/hu.bme.mit.incqueryd.core/src/main/java
[ERROR] /home/szarnyasg/git/incqueryd/hu.bme.mit.incqueryd.runtime/hu.bme.mit.incqueryd.core/src/main/scala
[ERROR] /home/szarnyasg/git/incqueryd/hu.bme.mit.incqueryd.runtime/hu.bme.mit.incqueryd.core/src/test/scala
[INFO] Compiling 50 source files to /home/szarnyasg/git/incqueryd/hu.bme.mit.incqueryd.runtime/hu.bme.mit.incqueryd.core/target/classes
[WARNING] warning: Class inventory.Inventory not found - continuing with a stub.
[WARNING] error: error while loading ArchUtil, class file '/home/szarnyasg/.m2/repository/hu/bme/mit/incqueryd/hu.bme.mit.incqueryd.arch.util/1.0.0-SNAPSHOT/hu.bme.mit.incqueryd.arch.util-1.0.0-SNAPSHOT.jar(hu/bme/mit/incqueryd/arch/util/ArchUtil.class)' is broken
[WARNING] (class java.lang.NullPointerException/null)
[WARNING] /home/szarnyasg/git/incqueryd/hu.bme.mit.incqueryd.runtime/hu.bme.mit.incqueryd.core/src/main/scala/hu/bme/mit/incqueryd/core/rete/actors/CoordinatorActor.scala:35: error: object ScalaChangeSet is not a member of package hu.bme.mit.incqueryd.core.rete.dataunits
[WARNING] import hu.bme.mit.incqueryd.core.rete.dataunits.ScalaChangeSet
[WARNING]        ^
[WARNING] one warning found
[WARNING] two errors found

It’s not broken, its missing. Make sure that you add the transitive dependencies manually if you mix manifest-first and POM-first projects.

Understanding pluginManagement/dependencyManagement

http://stackoverflow.com/a/10483432/90874

Troubleshooting

Please check the Troubleshooting section of the [[Maven and Eclipse]] page.

Authenticating to password-protected repositories

Create a settings.xml file in the ~/.m2 directory.

<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0
                          http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <servers>
    <server>
      <id></id>
      <username></username>
      <password></password>
    </server>
  </servers>
</settings>

Deploying to a local repository

Add the following under your POM’s <project> element. Replace /tmp/proj to a directory of your liking:

<distributionManagement>
	<repository>
		<id>maven-repository</id>
		<url>file:///tmp/proj</url>
	</repository>
</distributionManagement>

Use mvn deploy to deploy.

On more sophisticated methods and the tradeoffs of using GitHub as a Maven repository, read more on Stack Overflow.

Maven repositories

The Central Repository: the Maven Central.
Maven Repository: searches in ~200 repositories, including the Maven Central.
JCenter: fast repository with lots of packages (including a full mirror of the Maven Central), but only provides a very basic search engine. Even if you use JCenter (which is the default in most Gradle projects), you are generally better off searching for snippets in the Central Repository.
Eclipse Repository: the repository of the Eclipse project, with EMF, OCL, VIATRA, etc.