Set Up The Classpath
Contents
Add A Class-Path Entry To The Manifest
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Maven Archiver can add the classpath of your project to the manifest. This is done with the <addClasspath> configuration element.
<project> ... <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> ... <configuration> <archive> <manifest> <addClasspath>true</addClasspath> </manifest> </archive> </configuration> ... </plugin> </plugins> </build> ... <dependencies> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.1</version> </dependency> <dependency> <groupId>org.codehaus.plexus</groupId> <artifactId>plexus-utils</artifactId> <version>1.1</version> </dependency> </dependencies> ... </project>
The manifest produced using the above configuration would look like this:
Manifest-Version: 1.0 Created-By: Apache Maven ${maven.version} Build-Jdk: ${java.version} Class-Path: plexus-utils-1.1.jar commons-lang-2.1.jarMake The Jar Executable
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If you want to create an executable jar file, you need to configure Maven Archiver accordingly. You need to tell it which main class to use. This is done with the <mainClass> configuration element. Here is a sample pom.xml configured to add the classpath and use the class fully.qualified.MainClass as the main class:
<project> ... <build> <plugins> <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-jar-plugin</artifactId> ... <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <mainClass>fully.qualified.MainClass</mainClass> </manifest> </archive> </configuration> ... </plugin> </plugins> </build> ... <dependencies> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.1</version> </dependency> <dependency> <groupId>org.codehaus.plexus</groupId> <artifactId>plexus-utils</artifactId> <version>1.1</version> </dependency> </dependencies> ... </project>
The manifest produced using the above configuration would look like this:
Manifest-Version: 1.0 Created-By: Apache Maven ${maven.version} Build-Jdk: ${java.version} Main-Class: fully.qualified.MainClass Class-Path: plexus-utils-1.1.jar commons-lang-2.1.jarAltering The Classpath: Defining a Classpath Directory Prefix
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Sometimes it is useful to be able to alter the classpath, for example when creating skinny war-files. This can be achieved with the <classpathPrefix> configuration element.
<project> ... <build> <plugins> <plugin> <artifactId>maven-war-plugin</artifactId> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <classpathPrefix>lib/</classpathPrefix> </manifest> </archive> </configuration> </plugin> </plugins> </build> ... <dependencies> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.1</version> </dependency> <dependency> <groupId>org.codehaus.plexus</groupId> <artifactId>plexus-utils</artifactId> <version>1.1</version> </dependency> </dependencies> ... </project>
The manifest classpath produced using the above configuration would look like this:
Class-Path: lib/plexus-utils-1.1.jar lib/commons-lang-2.1.jar
Altering The Classpath: Using a Maven Repository-Style Classpath
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(Since: 2.3, see below)
Occasionally, you may want to include a Maven repository-style directory structure in your archive. If you wish to reference the dependency archives within those directories in your manifest classpath, try using the <classpathLayoutType> element with a value of 'repository', like this:
<project> ... <build> <plugins> <plugin> <artifactId>maven-jar-plugin</artifactId> <version>2.3</version> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <classpathPrefix>lib/</classpathPrefix> <classpathLayoutType>repository</classpathLayoutType> </manifest> </archive> </configuration> </plugin> </plugins> </build> ... <dependencies> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.1</version> </dependency> <dependency> <groupId>org.codehaus.plexus</groupId> <artifactId>plexus-utils</artifactId> <version>1.1</version> </dependency> </dependencies> ... </project>
The manifest classpath produced using the above configuration would look like this:
Class-Path: lib/org/codehaus/plexus/plexus-utils/1.1/plexus-utils-1.1.jar lib/commons-lang/commons-lang/2.1/commons-lang-2.1.jar
Altering The Classpath: Using a Custom Classpath Format
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(Since: 2.4)
At times, you may have dependency archives in a custom format within your own archive, one that doesn't conform to any of the above classpath layouts. If you wish to define a custom layout for dependency archives within your archive's manifest classpath, try using the <classpathLayoutType> element with a value of 'custom', along with the <customClasspathLayout> element, like this:
<project> ... <build> <plugins> <plugin> <artifactId>maven-war-plugin</artifactId> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <classpathLayoutType>custom</classpathLayoutType> <customClasspathLayout>WEB-INF/lib/$${artifact.groupIdPath}/$${artifact.artifactId}-$${artifact.version}$${dashClassifier?}.$${artifact.extension}</customClasspathLayout> </manifest> </archive> </configuration> </plugin> </plugins> </build> ... <dependencies> <dependency> <groupId>commons-lang</groupId> <artifactId>commons-lang</artifactId> <version>2.1</version> </dependency> <dependency> <groupId>org.codehaus.plexus</groupId> <artifactId>plexus-utils</artifactId> <version>1.1</version> </dependency> </dependencies> ... </project>This classpath layout is a little more involved than the previous examples. To understand how the value of the <customClasspathLayout> configuration is interpreted, it's useful to understand the rules applied when resolving expressions within the value:
- If present, trim off the prefix 'artifact.' from the expression.
- Attempt to resolve the expression as a reference to the Artifact using reflection (eg.
'artifactId'becomes a reference to the method'getArtifactId()'). - Attempt to resolve the expression as a reference to the ArtifactHandler of the current Artifact, again using reflection (eg.
'extension'becomes a reference to the method'getExtension()'). - Attempt to resolve the expression as a key in the special-case Properties instance, which contains the following mappings:
'dashClassifier': If the Artifact has a classifier, this will be'-$artifact.classifier', otherwise this is an empty string.'dashClassifier?': This is a synonym of'dashClassifier'.'groupIdPath': This is the equivalent of'$artifact.groupId', with all'.'characters replaced by'/'.
The manifest classpath produced using the above configuration would look like this:
Class-Path: WEB-INF/lib/org/codehaus/plexus/plexus-utils-1.1.jar WEB-INF/lib/commons-lang/commons-lang-2.1.jar
Handling Snapshot Versions
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(Since 2.4)
Depending on how you construct your archive, you may have the ability to specify whether snapshot dependency archives are included with the version suffix '-SNAPSHOT', or whether the unique timestamp and build-number for that archive is used. For instance, the Assembly Plugin allows you to make this decision in the <outputFileNameMapping> element of its <dependencySet> descriptor section.
Forcing the use of -SNAPSHOT versions when using the simple (default) or repository classpath layout
To force the use of '-SNAPSHOT' version naming, simply disable the <useUniqueVersions> configuration element, like this:
<useUniqueVersions>false</useUniqueVersions>
Forcing the use of -SNAPSHOT versions with custom layouts
To force the use of '-SNAPSHOT' version naming, simply replace '$artifact.version' with '$artifact.baseVersion' in the custom layout example above, so it looks like this:
<customClasspathLayout>WEB-INF/lib/${artifact.groupIdPath}/${artifact.artifactId}-${artifact.baseVersion}${dashClassifier?}.${artifact.extension}</customClasspathLayout>The full example configuration would look like this:
<project> ... <build> <plugins> <plugin> <artifactId>maven-war-plugin</artifactId> <configuration> <archive> <manifest> <addClasspath>true</addClasspath> <classpathLayoutType>custom</classpathLayoutType> <customClasspathLayout>WEB-INF/lib/${artifact.groupIdPath}/${artifact.artifactId}-${artifact.version}${dashClassifier?}.${artifact.extension}</customClasspathLayout> </manifest> </archive> </configuration> </plugin> </plugins> </build> ... </project>