Maven Dependency Jar

We will demonstrate how to build a Maven dependency jar file using the Maven Assembly Plugin. This task is useful when you wish to ease deployment by packaging all the project dependencies with the project deliverable inside the jar file.

Maven Assembly Plugin

In order to build the maven dependency jar file, we use the Maven assembly plugin. In this case we must add it to the plugins section of our pom.xml file.

he Maven plugin element allows us to define what plugins can hook into the maven build process. In this case we have defined that we want to use the maven assembly plugin to hook into the maven packaging phase to add the project dependencies to the packaged jar file.

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    <build>
        <finalName>my-dependency-jar</finalName>
        <plugins>
            <!-- download source code -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-eclipse-plugin</artifactId>
                <version>2.9</version>
                <configuration>
                    <downloadSources>true</downloadSources>
                    <downloadJavadocs>false</downloadJavadocs>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>${jdk.version}</source>
                    <target>${jdk.version}</target>
                </configuration>
            </plugin>

            <!-- Assembly Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4.1</version>
                <configuration>
                    <!-- get all project dependencies -->
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <!-- MainClass in mainfest file of jar file -->
                    <archive>
                        <manifest>
                            <mainClass>tutorials.maven.dependency.build.App</mainClass>
                        </manifest>
                    </archive>

                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <!-- bind to the packaging phase -->
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>

Maven Java Dependencies

As with any java project that does not exist in isolation we define the dependencies on which our project depends. These definitions are added to the dependencies element of the maven build file. Below we define junit as a test dependency. We also define joda time library as a project dependency. Joda time will be included within our build jar file.

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    <dependencies>
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
            <version>${jodatime.version}</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

Maven Build File

Below we show the complete maven build file.

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<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>tutorials.maven.dependency.build</groupId>
    <artifactId>my-dependency-jar</artifactId>
    <packaging>jar</packaging>
    <version>1.0-SNAPSHOT</version>
    <name></name>
    <url>http://maven.apache.org</url>

    <properties>
        <jdk.version>1.7</jdk.version>
        <jodatime.version>2.5</jodatime.version>
        <junit.version>4.11</junit.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>joda-time</groupId>
            <artifactId>joda-time</artifactId>
            <version>${jodatime.version}</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>${junit.version}</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <finalName>my-dependency-jar</finalName>
        <plugins>
            <!-- download source code -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-eclipse-plugin</artifactId>
                <version>2.9</version>
                <configuration>
                    <downloadSources>true</downloadSources>
                    <downloadJavadocs>false</downloadJavadocs>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>2.3.2</version>
                <configuration>
                    <source>${jdk.version}</source>
                    <target>${jdk.version}</target>
                </configuration>
            </plugin>

            <!-- Assembly Plugin -->
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-assembly-plugin</artifactId>
                <version>2.4.1</version>
                <configuration>
                    <!-- get all project dependencies -->
                    <descriptorRefs>
                        <descriptorRef>jar-with-dependencies</descriptorRef>
                    </descriptorRefs>
                    <!-- MainClass in mainfest file of jar file -->
                    <archive>
                        <manifest>
                            <mainClass>tutorials.maven.dependency.build.App</mainClass>
                        </manifest>
                    </archive>

                </configuration>
                <executions>
                    <execution>
                        <id>make-assembly</id>
                        <!-- bind to the packaging phase -->
                        <phase>package</phase>
                        <goals>
                            <goal>single</goal>
                        </goals>
                    </execution>
                </executions>
            </plugin>
        </plugins>
    </build>
</project>

Build With Maven

To build our maven dependency jar file we run the maven package target. Executing this target will enable the maven assembly plugin to hook into the package phase and produce the maven dependency jar file.

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mvn package

The above command when complete with output two jar files in the target directory. One jar file without dependencies and the other jar file with dependencies.

Conclusion

In this tutorial we looked at how to build a maven dependency jar. We also shown that a maven dependency jar allows us to ease the deployment burden by packaging all the projects dependencies with the project.