ClassNotFoundException in Maven project

问题

There is a maven based project, which can be built by maven install, but throw exception when run the out jar:

Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/commons/cli/CommandLineParser
Caused by: java.lang.ClassNotFoundException: org.apache.commons.cli.CommandLineParser
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:190)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:247)

I want to know why java can not find the maven dependency library ?

<?xml version="1.0" encoding="UTF-8"?>
<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>org.artofsolving.jodconverter</groupId>
  <artifactId>jodconverter-core</artifactId>
  <version>3.0-SNAPSHOT</version>
  <packaging>jar</packaging>

  <name>JODConverter - Core Library</name>
  <description>
    JODConverter converts office documents using OpenOffice.org
  </description>
  <url>http://jodconverter.googlecode.com</url>
  <licenses>
    <license>
      <name>GNU Lesser General Public License, Version 3 or later</name>
      <url>http://www.gnu.org/licenses/lgpl.html</url>
    </license>
  </licenses>
  <scm>
    <url>http://jodconverter.googlecode.com/svn/trunk/jodconverter-core</url>
    <connection>scm:svn:https://jodconverter.googlecode.com/svn/trunk/jodconverter-core/</connection>
  </scm>
  <inceptionYear>2003</inceptionYear>
  <developers>
    <developer>
      <id>mirko.nasato</id>
      <name>Mirko Nasato</name>
      <email>mirko@artofsolving.com</email>
    </developer>
  </developers>
  <contributors>
    <contributor>
      <name>Shervin Asgari</name>
      <email>shervin@asgari.no</email>
    </contributor>
  </contributors>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
  </properties>

  <repositories>
    <repository>
      <!-- required for org.hyperic:sigar -->
      <id>jboss-public-repository-group</id>
      <url>https://repository.jboss.org/nexus/content/groups/public-jboss/</url>
    </repository>
  </repositories>

  <dependencies>

    <!-- Required dependencies -->

    <dependency>
      <groupId>commons-io</groupId>
      <artifactId>commons-io</artifactId>
      <version>1.4</version>
    </dependency>
    <dependency>
      <groupId>org.openoffice</groupId>
      <artifactId>juh</artifactId>
      <version>3.2.1</version>
    </dependency>
    <dependency>
      <groupId>org.openoffice</groupId>
      <artifactId>ridl</artifactId>
      <version>3.2.1</version>
    </dependency>
    <dependency>
      <groupId>org.openoffice</groupId>
      <artifactId>unoil</artifactId>
      <version>3.2.1</version>
    </dependency>

    <dependency>
      <!-- for the command line tool -->
      <groupId>commons-cli</groupId>
      <artifactId>commons-cli</artifactId>
      <version>1.2</version>
    </dependency>

    <!-- Optional dependencies -->


    <dependency>
      <!-- for more robust process management -->
      <groupId>org.hyperic</groupId>
      <artifactId>sigar</artifactId>
      <version>1.6.5.132</version>
      <optional>true</optional>
    </dependency>
    <dependency>
      <!-- for JSON configuration -->
      <groupId>org.json</groupId>
      <artifactId>json</artifactId>
      <version>20090211</version>
      <optional>true</optional>
    </dependency>

    <!--  Test dependencies -->

    <dependency>
      <groupId>org.testng</groupId>
      <artifactId>testng</artifactId>
      <version>6.0.1</version>
      <scope>test</scope>
    </dependency>

  </dependencies>

  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-compiler-plugin</artifactId>
        <version>2.3.2</version>
        <configuration>
          <source>1.6</source>
          <target>1.6</target>
          <encoding>UTF-8</encoding>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-surefire-plugin</artifactId>
        <version>2.7.2</version>
        <configuration>
          <!-- don't run tests in parallel -->
          <perCoreThreadCount>false</perCoreThreadCount>
          <threadCount>1</threadCount>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>2.3.1</version>
        <configuration>
          <archive>
            <manifest>
              <mainClass>org.artofsolving.jodconverter.cli.Convert</mainClass>
              <addClasspath>true</addClasspath>
            </manifest>
          </archive>
        </configuration>
      </plugin>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-assembly-plugin</artifactId>
        <version>2.2-beta-5</version>
        <configuration>
          <descriptors>
            <descriptor>src/main/assembly/dist.xml</descriptor>
          </descriptors>
        </configuration>
      </plugin>
    </plugins>
  </build>

  <reporting>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-javadoc-plugin</artifactId>
        <version>2.7</version>
      </plugin>
      <plugin>
        <groupId>org.codehaus.mojo</groupId>
        <artifactId>cobertura-maven-plugin</artifactId>
        <version>2.4</version>
      </plugin>
    </plugins>
  </reporting>

</project>

回答1:

When running your Jar with java -jar, you're no longer running with the maven resolving of dependencies. You have to make sure that all the jars you depend on are available at the relative loacation specificied in the MANIFEST.mf file in your Jar. Usually, you would use the assembly plugin to create a distributable archive that creates this structure. Or you could use a uberjar/onejar plugin to included everything inside your Jar.

回答2:

You have 2 options to fix this:

Option 1 - use both plugins below to copy dependencies to a "lib" folder (see outputDirectory) and make your Runnable JAR know where they are (see classpathPrefix)

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<configuration>
    <archive>
        <manifest>
            <addClasspath>true</addClasspath>
            <classpathPrefix>lib/</classpathPrefix>
            <mainClass>example.MyMainClass</mainClass>
        </manifest>
    </archive>
</configuration>
</plugin>

<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<executions>
    <execution>
        <id>copy-dependencies</id>
        <phase>package</phase>
        <goals>
            <goal>copy-dependencies</goal>
        </goals>
        <configuration>
            <outputDirectory>${project.build.directory}/lib</outputDirectory>
            <overWriteReleases>false</overWriteReleases>
            <overWriteSnapshots>false</overWriteSnapshots>
            <overWriteIfNewer>true</overWriteIfNewer>
        </configuration>
    </execution>
</executions>

Option 2 - Use maven-assembly-plugin to create a single JAR with all dependencies included. (all dependencies are extracted and compressed together in the same JAR)

<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>with-dependencies</id>
<formats>
    <format>jar</format>
</formats>
<includeBaseDirectory>false</includeBaseDirectory>
<dependencySets>
    <dependencySet>
        <outputDirectory>/</outputDirectory>
        <useProjectArtifact>true</useProjectArtifact>
        <unpack>true</unpack>
        <scope>compile</scope>
    </dependencySet>
</dependencySets>

回答3:

I've seen the problem, too. Cobertura creates instrumented copies of all compiled classfiles (in target/classes) by bytecode manipulation. My jar file contained the instrumented class files (from target/generated-classes/cobertura), but cobertura.jar was missing. So, ClassNotFoundException was the right reaction.

However, since my POM doesn't contain any hint, which are the intended classes for packaging, Maven has the free choice ... and it uses the instrumented set of files.

My solution was really simple: mvn clean and mvn package. The first call removes all instrumented classes. Then, the second call finds only the uninstrumented classes without any external references to Cobertura.

来源：https://stackoverflow.com/questions/15871065/classnotfoundexception-in-maven-project

标签

jar

maven-3

classnotfoundexception