I'm using a Java Maven program and I don't know what to enter as the <mainClass>. 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 ???)
<build>
...
<plugins>
...
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.5.3</version>
<configuration>
<descriptors>
<descriptor>src/main/assembly/jar-with-dependencies.xml</descriptor>
</descriptors>
<archive>
<manifest>
<mainClass> ??? </mainClass>
</manifest>
</archive>
</configuration>
<executions>
<execution>
<id>make-assembly</id>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
</plugin>
...
</plugins>
...
</build>
How do I fix these errors?
Please follow the below snippet.. it works..
<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>com.xyz</groupId>
<artifactId>test</artifactId>
<packaging>jar</packaging>
<version>0.0.1-SNAPSHOT</version>
<name>TestProject</name>
<description>Sample Project</description>
<dependencies>
<!-- mention your dependencies here -->
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-compiler-plugin</artifactId>
<version>3.8.1</version>
<configuration>
<source>1.8</source>
<target>1.8</target>
</configuration>
</plugin>
<plugin>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-assembly-plugin</artifactId>
<version>3.1.1</version>
<configuration>
<archive>
<manifest>
<mainClass>com.xyz.ABC.</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>
</plugins>
</build>
</project>
Please note, you have to provide the full classified class name (class name including package name without .java or .class) of main class inside <mainClass></mainClass> tag.
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
add this to your pom.xml file:
<configuration>
<transformers>
<transformer implementation="org.apache.maven.plugins.shade.resource.ServicesResourceTransformer"/>
<transformer implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
<mainClass>sample.HelloWorldApplication</mainClass>
</transformer>
</transformers>
</configuration>
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.
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.
this worked for me....
I added the following line to properties in pom.xml
<properties>
<maven-jar-plugin.version>3.1.1</maven-jar-plugin.version>
</properties>
specify the main class location in pom under plugins
<build>
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<archive>
<index>true</index>
<manifest>
<mainClass>com.example.hadoop.wordCount.WordCountApp</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
</build>
TLDR : check if packaging element inside the pom.xml file is set to jar.
Like this - <packaging>jar</packaging>. 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 -
<?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>com.mycompany</groupId>
<artifactId>myproject</artifactId>
<version>1.0-SNAPSHOT</version>
<packaging>pom</packaging>
<properties>
<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>
</project>
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
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.
I got this error(classNotFoundException for main class), I actually changed pom version , so did maven install again and then error vanished.
The first thing i would suggest is to use the correct configuration for predefined descriptors.
<project>
[...]
<build>
[...]
<plugins>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<version>2.5.3</version>
<configuration>
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
[...]
</project>
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 <mainClass>...</mainClass> parameter.
Furthermore i recommend to stop using Maven 2 and move to Maven 3 instead.
Unless you need the 'maven-assembly-plugin' for reasons other than setting the mainClass, you could use the 'maven-jar-plugin' plugin.
<plugins>
<plugin>
<groupId>org.apache.maven.plugins</groupId>
<artifactId>maven-jar-plugin</artifactId>
<version>2.4</version>
<configuration>
<archive>
<index>true</index>
<manifest>
<mainClass>your.package.yourprogram.YourMainClass</mainClass>
</manifest>
</archive>
</configuration>
</plugin>
</plugins>
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");
}
}
I got it too, for me the problem got resolved after deleting the m2 folder (C:\Users\username.m2) and updating the maven project.
Source: Stackoverflow.com