Question

I’m having problems resolving sub-dependencies from a third-party package. I’m a bit of a Maven beginner. Basically it goes like this:

git clone git://github.com/unidata/thredds.git
cd thredds
mvn install

Everything works great and stuff is installed into ~/.m2. Now, I wrote my own code that uses the package that I just installed:

<?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/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>
    <groupId>test</groupId>
    <artifactId>test</artifactId>
    <packaging>jar</packaging>
    <version>0.1</version>
    <name>Test Package</name>

    <dependencies>
        <dependency>
            <groupId>edu.ucar</groupId>
            <artifactId>netcdf</artifactId>
            <version>4.3.8-SNAPSHOT</version>
        </dependency>
    </dependencies>
</project>

Ok, this also works great when I run mvn package. The netcdf artifact is found. Now, when I try to run my code, I start down a long ClassNotFoundException path, having to keep adding all of netcdf‘s dependencies to my classpath.

Am I doing something wrong, or should the thredds package and all its dependencies automatically be picked up?

edit: the thredds package has many sub-modules one of which is netcdf. My code only depends on the netcdf jar.

edit: the snapshot version is installed

$ ls -l ~/.m2/repository/edu/ucar/netcdf/4.3.8-SNAPSHOT/
total 4272
-rw-rw-r-- 1 nwatkins nwatkins     700 2012-03-29 23:23 maven-metadata-local.xml
-rw-rw-r-- 1 nwatkins nwatkins     182 2012-03-29 23:23 _maven.repositories
-rw-rw-r-- 1 nwatkins nwatkins 4357494 2012-03-29 23:23 netcdf-4.3.8-SNAPSHOT.jar
-rw-rw-r-- 1 nwatkins nwatkins    7840 2012-03-29 22:28 netcdf-4.3.8-SNAPSHOT.pom

edit: to run the code which is in a single file Test.java

$ java -cp target/test-0.1.jar Test

edit: first error message

$ java -cp target/test-0.1.jar Test

Exception in thread "main" java.lang.NoClassDefFoundError: ucar/ma2/InvalidRangeException
Caused by: java.lang.ClassNotFoundException: ucar.ma2.InvalidRangeException
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)

edit: then I just try to manually add the dependency jar to the class path

$ java -cp ../thredds/cdm/target/netcdf-4.3.8-SNAPSHOT.jar:target/test-0.1.jar Test

xception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
    at ucar.nc2.NetcdfFile.<clinit>(NetcdfFile.java:97)
    at Test.main(Test.java:37)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
    at java.net.URLClassLoader$1.run(URLClassLoader.java:217)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.net.URLClassLoader.findClass(URLClassLoader.java:205)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:321)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:294)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:266)
    ... 2 more

The slf4j package is also in ~/.m2. I stopped trying to add things to the classpath after this as it seemed like the wrong approach.
at java.lang.ClassLoader.loadClass(ClassLoader.java:266)

Answer 1

Two solutions here (the cause of the problem has been explained in several answers):

1.Use maven exec plugin to launch your app:

        <plugin>
            <groupId>org.codehaus.mojo</groupId>
            <artifactId>exec-maven-plugin</artifactId>
            <executions>
                <execution>
                    <goals>
                        <goal>exec</goal>
                    </goals>
                </execution>
            </executions>
            <configuration>
                <classpathScope>runtime</classpathScope>
                <executable>java</executable>
                <commandlineArgs>-classpath %classpath Test</commandlineArgs>
            </configuration>
        </plugin>

2.You can also package your jar with all its dependencies, using maven assembly plugin. To do that, you need to add the following to your plugins of your build:

<plugin>
    <artifactId>maven-assembly-plugin</artifactId>
    <version>2.3</version>
    <configuration>
      <descriptorRefs>
        <descriptorRef>jar-with-dependencies</descriptorRef>
      </descriptorRefs>
    </configuration>
    <executions>
        <execution>
        <id>build-package</id>
        <phase>package</phase>
            <goals>
                <goal>single</goal>
            </goals>
        </execution>
    </executions>
</plugin>

Then you can use the output jar created by maven assembly in your classpath arg