使用 Maven 2 构建可运行的 jar

Question

I'm relatively new to the Maven mantra, but I'm trying to build a command-line runnable jar with Maven. I've setup my dependencies, but when I run mvn install and attempt to run the jar, two things happen. First, no main class is found, which is correctable. When I've corrected this, I get errors on run stating that classes cannot be found.

Maven is not packaging my dependency libraries inside of the jar, so I am unable to run the jar as a stand-alone application. How do I correct this?

Answer 1

The easiest way to do this would be to create an assembly using the maven-assembly-plugin and the predefined jar-with-dependencies descriptor. You'll also need to generate a manifest with a main-class entry for this uber jar. The snippet below shows how to configure the assembly plugin to do so:

<build>
  <plugins>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>fully.qualified.MainClass</mainClass>
          </manifest>
        </archive>
      </configuration>
    </plugin>
  </plugins>
</build>

Then, to generate the assembly, just run:

mvn assembly:assembly

If you want to generate the assembly as part of your build, simply bind the assembly:single mojo to the package phase:

<build>
  <plugins>
    <plugin>
      <artifactId>maven-assembly-plugin</artifactId>
      <configuration>
        <descriptorRefs>
          <descriptorRef>jar-with-dependencies</descriptorRef>
        </descriptorRefs>
        <archive>
          <manifest>
            <mainClass>fully.qualified.MainClass</mainClass>
          </manifest>
        </archive>
      </configuration>
      <executions>
        <execution>
          <phase>package</phase>
          <goals>
            <goal>single</goal>
          </goals>
        </execution>
      </executions>
    </plugin>
  </plugins>
</build>

And simply run:

mvn package

Answer 2

Maven is not packaging your dependencies inside your jar file, because you don't usually do this with Java programs.

Instead you deliver the dependencies together with your jar file and mention them in the Class-Path header of the Manifest .

To go this route, you'll need to enable the addClasspath property (documented here ) for the maven-jar-plugin .

If you really want to include all your dependencies in your jar file, then you can use the Maven Assembly plugin to create a jar-with-dependencies .

Answer 3

This is what I would do for small projects. Most of the time you don't want one huge jar.

to build: mvn clean dependency:copy-dependencies package

to execute ( in target dir ): java -cp myjar.jar:./dependency/* com.something.MyClass

Answer 4

I Agree with Joachim Sauer,

Instead of using jar-with-dependency you should configure the jar plugin like that in your pom.xml:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-jar-plugin</artifactId>
    <version>2.4</version>
    <configuration>
        <archive>
            <index>true</index>
            <manifest>
                <addClasspath>true</addClasspath>
                <mainClass>[mainClassFullName]</mainClass>
            </manifest>
            <manifestEntries>
                <mode>development</mode>
                <url>${project.url}</url>
                <key>value</key>
            </manifestEntries>
        </archive>
    </configuration>
</plugin>

And use this assembly configuration to add the jar dependencies to you assembly:

<assembly xmlns="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0" 
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://maven.apache.org/plugins/maven-assembly-plugin/assembly/1.1.0 http://maven.apache.org/xsd/assembly-1.1.0.xsd">
  <id>zip-with-jars</id>
  <formats>
    <format>zip</format>
  </formats>
  <includeBaseDirectory>false</includeBaseDirectory>
  <dependencySets>
    <dependencySets>
    <dependencySet>
    <outputDirectory>/</outputDirectory>
    <useProjectArtifact>true</useProjectArtifact>
    <unpack>false</unpack>
    <scope>runtime</scope>
    </dependencySet>
</dependencySets>
  </dependencySets>
</assembly>

Answer 5

Just add the below code in pom.xml and Run as: maven:install . The jar will be created in target folder of eclipse which can be used as "java -jar Hello.jar" . but make sure that name of main class is given com.abc.HelloWorld.java

<build>
<plugins>
<plugin>
<groupid>org.apache.maven.plugins</groupid>
<artifactid>maven-shade-plugin</artifactid>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>shade</goal>
</goals>
<configuration>
<finalname>HelloW</finalname>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<manifestentries>
<main-class>com.abc.HelloWorld.java</main-class>
<build-number>1</build-number>
</manifestentries>
</transformer>
</transformers>
</configuration>
</execution>
</executions>
</plugin>
</plugins>

</build>

Answer 6

I have a spring boot application, and the jar created by maven package can be run without setting up additional plugins.

Inside my pom.xml:

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.6.12</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

https://spring.io/projects/spring-boot