Maven Error Could not find or load main class

Question

I m using a Java Maven program and I don t know what to enter as the  lt mainClass gt    I ve tried all kinds of things based off of numerous stackoverflow questions  but they are not solving the error   Each time it says   Maven Error  Could not find or load main class       I have this written inside my pom xml  minus the          lt build gt           lt plugins gt             lt plugin gt           lt artifactId gt maven-assembly-plugin lt  artifactId gt           lt version gt 2 5 3 lt  version gt           lt configuration gt               lt descriptors gt                   lt descriptor gt src main assembly jar-with-dependencies xml lt  descriptor gt               lt  descriptors gt               lt archive gt                   lt manifest gt                       lt mainClass gt       lt  mainClass gt                   lt  manifest gt               lt  archive gt           lt  configuration gt           lt executions gt               lt execution gt               lt id gt make-assembly lt  id gt               lt phase gt package lt  phase gt               lt goals gt                   lt goal gt single lt  goal gt               lt  goals gt               lt  execution gt           lt  executions gt       lt  plugin gt           lt  plugins gt           lt  build gt    How do I fix these errors

User · Answer

specify the main class location in pom under plugins   lt build gt           lt plugins gt               lt plugin gt                   lt groupId gt org apache maven plugins lt  groupId gt                   lt artifactId gt maven-jar-plugin lt  artifactId gt                   lt version gt 2 4 lt  version gt                   lt configuration gt                       lt archive gt                           lt index gt true lt  index gt                           lt manifest gt                               lt mainClass gt com example hadoop wordCount WordCountApp lt  mainClass gt                           lt  manifest gt                       lt  archive gt                   lt  configuration gt               lt  plugin gt           lt  plugins gt       lt  build gt

User · Answer

TLDR   check if packaging element inside the pom xml file is set to jar   Like this -  lt packaging gt jar lt  packaging gt   If it set to pom your target folder will not be created even after you Clean and Build your project and Maven executable won t be able to find  class files  because they don t exist   after which you get Error  Could not find or load main class your package name MainClass     After creating a Maven POM project in Netbeans 8 2  the content of the default pom xml file are as follows -   lt  xml version  1 0  encoding  UTF-8   gt   lt 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  gt      lt modelVersion gt 4 0 0 lt  modelVersion gt      lt groupId gt com mycompany lt  groupId gt      lt artifactId gt myproject lt  artifactId gt      lt version gt 1 0-SNAPSHOT lt  version gt      lt packaging gt pom lt  packaging gt      lt properties gt          lt project build sourceEncoding gt UTF-8 lt  project build sourceEncoding gt      lt  properties gt   lt  project gt    Here packaging element is set to pom  Hence the target directory is not created as we are not enabling maven to package our application as a jar file  Change it to jar then Clean and Build your project  you should see target directory created at root location  Now you should be able to run that java file with main method   When no packaging is declared  Maven assumes the packaging as jar  Other core packaging values are pom  war  maven-plugin  ejb  ear  rar  These define the goals that execute on each corresponsding build life-cycle phase of that package  See more here

User · Answer

I got it too  for me the problem got resolved after deleting the m2 folder  C  Users username m2  and updating the maven project

User · Answer

add this to your pom xml file    lt configuration gt      lt transformers gt          lt transformer implementation  org apache maven plugins shade resource ServicesResourceTransformer   gt          lt transformer implementation  org apache maven plugins shade resource ManifestResourceTransformer  gt            lt mainClass gt sample HelloWorldApplication lt  mainClass gt          lt  transformer gt      lt  transformers gt   lt  configuration gt    and add the class name of your project  full path  along with the package name like  com packageName className  which consists of the main method having  run  method in it  And instead of your       write   mainClass  which will automatically get the className which you have mentioned above   Then try command mvn clean install and mvn -jar  jar file name jar  server  yaml file name yml   I hope it will work normally and server will start at the specified port

User · Answer

I got this error classNotFoundException for main class   I actually changed pom version   so did maven install again and then error vanished

User · Answer

Please follow the below snippet   it works     lt 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  gt       lt modelVersion gt 4 0 0 lt  modelVersion gt       lt groupId gt com xyz lt  groupId gt       lt artifactId gt test lt  artifactId gt       lt packaging gt jar lt  packaging gt       lt version gt 0 0 1-SNAPSHOT lt  version gt       lt name gt TestProject lt  name gt       lt description gt Sample Project lt  description gt       lt dependencies gt           lt  -- mention your dependencies here -- gt       lt  dependencies gt       lt build gt           lt plugins gt               lt plugin gt                   lt groupId gt org apache maven plugins lt  groupId gt                   lt artifactId gt maven-compiler-plugin lt  artifactId gt                   lt version gt 3 8 1 lt  version gt                   lt configuration gt                       lt source gt 1 8 lt  source gt                       lt target gt 1 8 lt  target gt                   lt  configuration gt               lt  plugin gt               lt plugin gt               lt plugin gt                   lt groupId gt org apache maven plugins lt  groupId gt                   lt artifactId gt maven-assembly-plugin lt  artifactId gt                   lt version gt 3 1 1 lt  version gt                   lt configuration gt                       lt archive gt                           lt manifest gt                               lt mainClass gt com xyz ABC  lt  mainClass gt                           lt  manifest gt                       lt  archive gt                       lt descriptorRefs gt                           lt descriptorRef gt jar-with-dependencies lt  descriptorRef gt                       lt  descriptorRefs gt                   lt  configuration gt                   lt executions gt                       lt execution gt                           lt id gt make-assembly lt  id gt                           lt phase gt package lt  phase gt                           lt goals gt                               lt goal gt single lt  goal gt                           lt  goals gt                       lt  execution gt                   lt  executions gt               lt  plugin gt           lt  plugins gt       lt  build gt   lt  project gt    Please note  you have to provide the full classified class name  class name including package name without  java or  class  of main class inside  lt mainClass gt  lt  mainClass gt  tag

User · Answer

I got it too  the key was to change the output folder from bin to target classes  It seems that in Eclipse  when converting a project to Maven project  this step is not done automatically  but Maven project will not look for main class based on bin  but will on target classes

User · Answer

For me the problem was nothing to do with Maven but to do with how I was running the  jar  I wrote some code and packaged it as a  jar with Maven  I ran it with  java target gs-maven-0 1 0 jar   and got the error in the OP  Actually you need the -jar option   java -jar target gs-maven-0 1 0 jar

User · Answer

Unless you need the  maven-assembly-plugin  for reasons other than setting the mainClass  you could use the  maven-jar-plugin  plugin         lt plugins gt           lt plugin gt               lt groupId gt org apache maven plugins lt  groupId gt               lt artifactId gt maven-jar-plugin lt  artifactId gt               lt version gt 2 4 lt  version gt               lt configuration gt                   lt archive gt                       lt index gt true lt  index gt                       lt manifest gt                           lt mainClass gt your package yourprogram YourMainClass lt  mainClass gt                       lt  manifest gt                   lt  archive gt               lt  configuration gt           lt  plugin gt        lt  plugins gt    You can see the plugin in practise in the ATLauncher   The  mainClass  element should be set to the class that you have the entry point to your program in eg   package your package yourprogram   public class YourMainClass        public static void main String   args            System out println  Hello World

User · Answer

this worked for me     I added the following line to properties in pom xml  lt properties gt       lt maven-jar-plugin version gt 3 1 1 lt  maven-jar-plugin version gt   lt  properties gt

User · Answer

I got this error using Maven  and I discovered the solution   Error  Could not find or load main class com mycompany testapifactory Main   I m using java JDK version 1 7 on Linux  my pom xml file was the default generated by Netbeans and I was using these commands to compile  which do work fine with a normal hello-world java application   mvn clean compile java -jar target TestAPIFactory-1 0-SNAPSHOT jar com mycompany testapifactory Main   What happened   It turns out my problem was that my Main method was extending something Exotic like this   public class Main extends SomeExoticLibraryClass      public static void main String   args                           It was this extending of the main class that caused the above error   TLDR solution   Make sure your main class isn t extending any 3rd party classes   Refactor those out and away into their own classes   That error message is awful  and requires process of elimination to find out what to do

User · Answer

The first thing i would suggest is to use the correct configuration for predefined descriptors    lt project gt             lt build gt                 lt plugins gt         lt plugin gt           lt artifactId gt maven-assembly-plugin lt  artifactId gt           lt version gt 2 5 3 lt  version gt           lt configuration gt             lt descriptorRefs gt               lt descriptorRef gt jar-with-dependencies lt  descriptorRef gt             lt  descriptorRefs gt           lt  configuration gt                 lt  project gt    To configure the main class you need to know the package and name of the class you would like to use which should be given into  lt mainClass gt     lt  mainClass gt  parameter   Furthermore i recommend to stop using Maven 2 and move to Maven 3 instead

[java] Maven Error: Could not find or load main class

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