I am a beginner in maven and now I'm confused with the difference between these maven plugins. Is these all create jar files? now my questions are
what's the difference between the jar created in each plugins.( assembly plugin, jar-plugin, shaded plugin)
The purpose of each plugin. ( assembly, jar plugin, shaded plugin )
I know even without specifying any of these plugins once type mvn package there will be a jar output. What is the difference of the output jar without these plugins and the output jar with these plugins?. TIA
In Maven, there are two kinds of plugins, build and reporting: Build plugins are executed during the build and configured in the <build/> element. Reporting plugins are executed during the site generation and configured in the <reporting/> element.
This plugin provides the capability to package the artifact in an uber-jar, including its dependencies and to shade - i.e. rename - the packages of some of the dependencies.
The Assembly Plugin for Maven enables developers to combine project output into a single distributable archive that also contains dependencies, modules, site documentation, and other files. Your project can easily build distribution "assemblies" using one of the prefabricated assembly descriptors.
maven-shade-plugin : It packages all dependencies into one uber-jar. It can also be used to build an executable jar by specifying the main class. This plugin is particularly useful as it merges content of specific files instead of overwriting them by Relocating Classes.
maven-jar-plugin
: This plugin provides the capability to build and sign JARs. But it just compiles the java files under src/main/java
and src/main/resources/
. It doesn't include the dependencies JAR files.maven-assembly-plugin
: This plugin extracts all dependency JARs into raw classes and groups them together. It can also be used to build an executable JAR by specifying the main class. It works in project with less dependencies only; for large project with many dependencies, it will cause Java class names to conflict.maven-shade-plugin
: It packages all dependencies into one uber-JAR. It can also be used to build an executable JAR by specifying the main class. This plugin is particularly useful as it merges content of specific files instead of overwriting them by relocating classes. This is needed when there are resource files that have the same name across the JARs and the plugin tries to package all the resource files together.Refer: comparison:maven plugin jar,assembly,shade
Jar plugin
Let's see what the following command can tell.
mvn help:describe -Dplugin=org.apache.maven.plugins:maven-jar-plugin
It has 3 goals, help
, jar
and test-jar
. I believe you are mostly interested in the jar
goal, which according to the description does the following:
Build a JAR from the current project.
As a side note, executing mvn help:effective-pom
on a project with packaging set to jar
, shows that this plugin is automatically configured and gets executed during the package
phase.
<plugin> <artifactId>maven-jar-plugin</artifactId> <version>2.4</version> <executions> <execution> <id>default-jar</id> <phase>package</phase> <goals> <goal>jar</goal> </goals> </execution> </executions> </plugin>
Assembly plugin
This one serves a different purpose. It has 8 goals, but 6 of them are deprecated. So apart from the help
goal, this leaves us with the single
goal.
mvn help:describe -Dplugin=org.apache.maven.plugins:maven-assembly-plugin
Assemble an application bundle or distribution from an assembly descriptor. This goal is suitable either for binding to the lifecycle or calling directly from the command line (provided all required files are available before the build starts, or are produced by another goal specified before this one on the command line).
You may use the assembly plugin when you want to deliver more than your project's artifact (JAR, WAR, etc.), but the configuration goes in another file.
Shade plugin
The description of the main goal is a bit disappointing.
mvn help:describe -Dplugin=org.apache.maven.plugins:maven-shade-plugin
Mojo that performs shading delegating to the Shader component.
You mostly want to use this plugin if you want to produce an uber-jar, which is your artifact in a JAR with all its transitive dependencies in it.
Basicly, if you're building a library, you'll stick with the default JAR plugin. If you're building an application, you could consider using the shade plugin, though to me, it's kind of quick and dirty. If uber-jar is not your taste or the distribution cannot fit inside a single JAR (external configuration, native dependencies, etc.) then you should go for the assembly plugin.
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