maven slf4j how to add to classpath - eclipse

Question

I am completely new to maven, took a couple of tutorials and decided to do some logging with slf4j but I keep getting an error that the class cannot be found.
After some internet searches I have tried to add plugins etc. to my pom.xml but nothing seem to work.
The exception is this:
java -cp target/MavenTest-1.0-SNAPSHOT.jar org.nilun.App
Hello World!
Exception in thread "main" java.lang.NoClassDefFoundError: org/slf4j/LoggerFactory
at org.nilun.App.main(App.java:15)
Caused by: java.lang.ClassNotFoundException: org.slf4j.LoggerFactory
at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:331)
at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
... 1 more
Here is a snippet of my pom.xml
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<scope>test</scope>
<version>4.11</version>
</dependency>
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-api</artifactId>
<version>1.7.12</version>
</dependency>
</dependencies>
The very simple class
package org.nilun;
import org.slf4j.*;
/**
* Hello world!
*
*/
public class App
{
public static void main( String[] args )
{
System.out.println( "Hello World!" );
Logger logger = LoggerFactory.getLogger(App.class);
logger.info("Hello World!");
}
}
The jar file is located in my $HOME/development/lib
And of course it has been added to my eclipse build path
Any ideas would be welcomed to solve this.
Thanks!

Answer 1

I think the way to execute the program is the problem. If I execute your code in Eclipse, it works just fine (after adding this dependency
<dependency>
<groupId>org.slf4j</groupId>
<artifactId>slf4j-simple</artifactId>
<version>1.7.12</version>
</dependency>
which you will need to fix another exception, according to SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder"). However, when I use "java -cp target/MavenTest-1.0-SNAPSHOT.jar org.nilun.App", I get the same exception as you.
Edit: To create a .jar file containing dependencies, take a look at the Maven Assembly Plugin (here is a nice and short introduction: https://maven.apache.org/plugins/maven-assembly-plugin/usage.html). You need to add the following to your POM:
<build>
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.5.5</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
<archive>
<manifest>
<mainClass>de.clanue.MavenTest.App</mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id> <!-- this is used for inheritance merges -->
<phase>package</phase> <!-- bind to the packaging phase -->
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
</plugins>
</build>
Now, building the project with maven creates a file "MavenTest-0.0.1-SNAPSHOT-jar-with-dependencies.jar" in the target folder. It contains your dependencies and you can run it using "java -jar target/MavenTest-0.0.1-SNAPSHOT-jar-with-dependencies.jar".

Answer 2

Hi Lupa and thank you for the help.
With your guidance I got it to work.
What I did was to add the following plugins to
copy the folders to the target/lib folder
Add the /lib....jar to the manifest file.
Thanks again for the help!
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.6</version>
<configuration>
<archive>
<manifest>
<addClasspath>true</addClasspath>
<classpathPrefix>lib</classpathPrefix>
</manifest>
</archive>
</configuration>
</plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-dependency-plugin</artifactId>
<version>2.10</version>
<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>
</plugin>
</plugins>
</build>