2

I'm trying to make a little program using maven. I'm using a template from a prof at my university and I'd like to use log4j for logging. When I run the program in eclipse it works fine. However when I create the jar with "mvn install" and try to run the program in cmd I get a NoClassDefFoundError

C:\eclipse_workspace_buchhaltung\Buchhaltung\target>c:\jdk-11.0.4\bin\java.exe -jar Buchhaltung-1.0.0-SNAPSHOT.jar Exception in thread "main" java.lang.NoClassDefFoundError: org/apache/logging/log4j/LogManager at ch.hslu.demo.DemoKlasse.<clinit>(DemoKlasse.java:11) Caused by: java.lang.ClassNotFoundException: org.apache.logging.log4j.LogManager at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:583) at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:178) at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:521) ... 1 more

The DemoKlasse I'm using to try out things looks like the following:

package ch.hslu.demo; import java.time.LocalDateTime; import java.util.Scanner; import org.apache.logging.log4j.LogManager; import org.apache.logging.log4j.Logger; public class DemoKlasse { private static final Logger logger = LogManager.getLogger(DemoKlasse.class); // that's line 11 public static void main(String[] args) { logger.info("DemoKlasse gestartet: " + LocalDateTime.now()); System.out.println("Dies ist eine Testklasse!"); String eingabe = ""; Scanner sc = new Scanner(System.in); while(true) { System.out.println("Bitte geben Sie etwas ein. Beenden mit \"exit\""); eingabe = sc.nextLine(); logger.info("Eingabe lautet: " + eingabe); if(eingabe.equalsIgnoreCase("exit")) { System.out.println("Das Programm wird beendet"); logger.info("Exit wurde eingegeben: " + LocalDateTime.now()); sc.close(); System.exit(1); } } } }

My pom with the log4j part looks like this:

 <properties> ... <log4j2.version>2.12.1</log4j2.version> <junit5.version>5.5.1</junit5.version> </properties> <dependencyManagement> <dependencies> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-api</artifactId> <version>${log4j2.version}</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.apache.logging.log4j</groupId> <artifactId>log4j-core</artifactId> <version>${log4j2.version}</version> <scope>runtime</scope> </dependency> ...

I've also found this here: NoClassDefFoundError on Maven dependency I tried using the maven-shade-plugin and the maven-assembly-plugin but I still can't make it work.

Has anyone an idea why I can't make such a simple program work?

Improve this question
3
  • If you are not using any plugin like shade/assembly and so on to create a uber jar, dependencies don't get packaged. If it is just default jar generated by maven will have only your classes not the dependencies. Commented Dec 23, 2019 at 17:52
  • You can check the content of your jar by extracting it, and see what are all the classes is packaged inside. Commented Dec 23, 2019 at 17:54
  • refer to stackoverflow.com/questions/26338387/… Commented Dec 23, 2019 at 17:56

1 Answer 1

Reset to default
2

What are you doing?

You are creating a JAR file containing your code (and a Manifest file that points to your main class).

What is the problem?

You are exporting your code to a JAR file but the dependencies are not exported. Obviously, your program needs the dependencies to run(logging libriaries are not essention but other libs are).

How to solve it?

You said, you tried the shadow and the assembly plugin. You can add the dependencies with both. I think you just configured it incorrectly.

With the maven-assembly-plugin, you need to create a jar-with-dependencies and you shouldn't forget about your main class.

For example, you could use the following configuration(replace fully-qualified-main-class with the package name of your main class followed by the name of the main class(seperated by dots):

<plugin> <artifactId>maven-assembly-plugin</artifactId> <configuration> <archive> <manifest> <mainClass>fully.qualified.MainClass</mainClass> </manifest> </archive> <descriptorRefs> <descriptorRef>jar-with-dependencies</descriptorRef> </descriptorRefs> </configuration> <executions> <execution> <id>make-assembly</id> <phase>package</phase> <goals> <goal>single</goal> </goals> </execution> </executions> </plugin>

After that, you can create the JAR with the command mvn package.

Make sure to execute the jar-with-dependencies and not the JAR created by the maven-jar-plugin.

other possible problems

It is possible that your program declares log4j with the scope provided. In that case, log4j is not included in your jar-with-dependencies.

See https://stackoverflow.com/a/574650/10871900

Improve this answer
Sign up to request clarification or add additional context in comments.

1 Comment

Thanks for your great answer. Now I understand what the problem was and what the solution does and it also works for my program.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.