Eclipse Maven project ClassNotFoundException at run time

Question

I would like to try CRS transformations with GeoTools. I created a new Maven project in Eclipse and set the dependencies. The pom.xml file contains the following:

<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>org.geotools</groupId>
  <artifactId>geotools-homolosine</artifactId>
  <version>0.0.1-SNAPSHOT</version>

  <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <geotools.version>21-SNAPSHOT</geotools.version>
    </properties>

  <dependencies>
        <dependency>
          <groupId>org.geotools</groupId>
          <artifactId>gt-referencing</artifactId>
          <version>${geotools.version}</version>
        </dependency>
        <dependency>
          <groupId>org.geotools</groupId>
          <artifactId>gt-epsg-hsql</artifactId>
          <version>${geotools.version}</version>
        </dependency>
        <dependency>
          <groupId>org.geotools</groupId>
          <artifactId>gt-epsg-extension</artifactId>
          <version>${geotools.version}</version>
        </dependency>
    </dependencies>

    <repositories>
        <repository>
            <id>maven2-repository.dev.java.net</id>
            <name>Java.net repository</name>
            <url>http://download.java.net/maven/2</url>
        </repository>
        <repository>
            <id>osgeo</id>
            <name>Open Source Geospatial Foundation Repository</name>
            <url>http://download.osgeo.org/webdav/geotools/</url>
        </repository>
        <repository>
          <snapshots>
            <enabled>true</enabled>
          </snapshots>
          <id>boundless</id>
          <name>Boundless Maven Repository</name>
          <url>http://repo.boundlessgeo.com/main</url>
        </repository>
    </repositories>

</project>

The Maven commands to clean and install both complete successfully and the libraries downloaded are shown by Eclipse within the Maven Dependencies folder.

I then created a simple programme:

import org.geotools.referencing.CRS;
import org.geotools.referencing.crs.DefaultGeographicCRS;
import org.opengis.referencing.crs.CoordinateReferenceSystem;
import org.opengis.referencing.operation.MathTransform;

public class Transformation 
{
    public static void main(String[] args) 
    {
        // TODO Auto-generated method stub
        CoordinateReferenceSystem WORLDCRS = DefaultGeographicCRS.WGS84;
        CoordinateReferenceSystem crs;
        MathTransform transform = null;

        try 
        {
            crs = CRS.decode("3035");
            transform = CRS.findMathTransform(WORLDCRS, crs, true);
        } 
        catch (Exception e) 
        {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        System.out.println(transform.toWKT());
        System.out.println(transform.getClass().getCanonicalName());
    }
}

The Java editor reports no errors or warnings. However, when I run the programme (Right click > Run as > Java Application), the Console shows the following:

Error: A JNI error has occurred, please check your installation and try again
Exception in thread "main" java.lang.NoClassDefFoundError: org/opengis/referencing/crs/CoordinateReferenceSystem
    at java.lang.Class.getDeclaredMethods0(Native Method)
    at java.lang.Class.privateGetDeclaredMethods(Class.java:2701)
    at java.lang.Class.privateGetMethodRecursive(Class.java:3048)
    at java.lang.Class.getMethod0(Class.java:3018)
    at java.lang.Class.getMethod(Class.java:1784)
    at sun.launcher.LauncherHelper.validateMainClass(LauncherHelper.java:544)
    at sun.launcher.LauncherHelper.checkAndLoadMain(LauncherHelper.java:526)
Caused by: java.lang.ClassNotFoundException: org.opengis.referencing.crs.CoordinateReferenceSystem
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    ... 7 more

Somehow the Maven dependencies are not reachable at run time. What could be amiss?

Answer 1

This error was caused by the absence of a build section in the pom.xml file. Among other things, this section identifies the main class of the project. Apparently, Eclipse is not able to lauch the project correctly without this information. Here is the build section matching the project described above:

<build>
 <plugins>
  <plugin>
   <groupId>org.codehaus.mojo</groupId>
   <artifactId>exec-maven-plugin</artifactId>
   <version>1.1.1</version>
   <executions>
    <execution>
     <phase>test</phase>
     <goals>
      <goal>java</goal>
     </goals>
     <configuration>
      <mainClass>org.ldesousa.Transformation</mainClass>
     </configuration>
    </execution>
   </executions>
  </plugin>
 </plugins>
</build>

Note that I had to include the main into a package (org.ldesousa in this case).