Maven没有安装依赖项

Question

I have the following (short) pom.xml for a Maven project. I added the com.google.collections dependency, yet I do not see any of the classes for this dependency on in the /target/classes directory when I do a maven clean package . Furthermore, when I execute the JAR, I get an error ( java.lang.NoClassDefFoundError: com/google/common/collect/Iterables ). What am I forgetting to do?

<project>
  <groupId>edu.berkeley</groupId>
  <artifactId>java-page-rank</artifactId>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
        </configuration>
      </plugin>
    </plugins>
  </build>
  <modelVersion>4.0.0</modelVersion>
  <name>PageRank</name>
  <packaging>jar</packaging>
  <version>1.0</version>
  <dependencies>
    <dependency> <!-- Spark dependency -->
      <groupId>org.apache.spark</groupId>
      <artifactId>spark-core_2.10</artifactId>
      <version>1.6.0</version>
    </dependency>
    <!-- http://mvnrepository.com/artifact/com.google.collections/google-collections -->
    <dependency>
      <groupId>com.google.collections</groupId>
      <artifactId>google-collections</artifactId>
      <version>1.0</version>
    </dependency>
  </dependencies>
</project>

Answer 1

You won't see dependencies in target/classes , those are just used for compilation and taken from your $HOME/.m2/repository .

If you need to run the resulting jar you will need to either:

1. Construct the full classpath with all the dependencies (jars that you use from the local maven repository $HOME/.m2/repository .
2. Create an uberjar that will contain all the classes packaged into a single jar (you can use maven assembly plugin or shade plugin for that).

Eg for assembly plugin you will need to add plugin to the plugins section:

  <plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>2.6</version>
    <configuration>
      <descriptorRefs>
        <descriptorRef>jar-with-dependencies</descriptorRef>
      </descriptorRefs>
      <archive>
        <manifest>
          <mainClass>package.for.the.start.Main</mainClass>
        </manifest>
      </archive>
    </configuration>
  </plugin>

And later execute maven with assembly:single , eg:

mvn clean package assembly:single

The resulting jar will be target/java-page-rank-1.0-SNAPSHOT-jar-with-dependencies.jar .

Answer 2

Use maven-assembly-plugin instead of maven-compiler-plugin if you want your jar to contain all the dependencies

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.6</version>
<configuration>
    <descriptorRefs>
        <descriptorRef>jar-with-dependencies</descriptorRef>
    </descriptorRefs>
    <archive>
        <manifest>
            <mainClass>Main</mainClass>
        </manifest>
    </archive>
</configuration>
<executions>
    <execution>
        <phase>package</phase>
        <goals>
            <goal>single</goal>
        </goals>
    </execution>
</executions>