Maven build Error: Could not find or load main class

Question

I have problem after build project on maven in jar.

I make package and create .jar file:

mvn package

after i run my jar file

java -jar artifactId.jar

and get error:

Error: Could not find or load main class com.emercit.app.App

If i run class in target directory, i get similar error:

cd target/classes/com/emercit/app
java App
Error: Could not find or load main class App

My code in App class:

package com.emercit.app;

public class App extends Application {

   /**

     Program code

  **/

    }

public static void main (String[] args) {


    //Init form
   Thread myThready = new Thread(() -> {
        launch(args);
    });
    myThready.start();

    }
 }

My build properties in pom.xml:

 <build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <configuration>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
        </plugin>


        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-jar-plugin</artifactId>
            <configuration>
                <archive>
                    <manifest>
                        <addClasspath>false</addClasspath>
                        <classpathPrefix>lib/</classpathPrefix>
                        <mainClass>com.emercit.app.App</mainClass>
                    </manifest>
                </archive>
            </configuration>
        </plugin>

        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <executions>
                <execution>
                    <id>copy</id>
                    <phase>install</phase>
                    <goals>
                        <goal>copy-dependencies</goal>
                    </goals>
                    <configuration>
                        <outputDirectory>
                            ${project.build.directory}/lib
                        </outputDirectory>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

You shouldn't run `App` in `target/classes/com/emercit/app` from console, you run `com.emercit.app.App` from `target/classes`. — Jiri Tousek, Mar 09 '17 at 07:05
`Error: Could not find or load main class App` means that the class App were not found - are you sure that maven even generates the classfiles for you? Have you placed the App-class under the correct project structure? Meaning `/src/main/com/../../App`? If not, you'll might have to add a ``-configuration. — vegaasen, Mar 09 '17 at 07:06
No matter. I get Error: Could not find or load main class com.emercit.app.App — Wolfgang, Mar 09 '17 at 07:07
@Sterkhov dont forget the fact that this still is java cmdline application. With that being said, you lack buildmanifest.mf file — Malakai, Mar 09 '17 at 07:07
Possible duplicate of [What does "Could not find or load main class" mean?](http://stackoverflow.com/questions/18093928/what-does-could-not-find-or-load-main-class-mean) — Seelenvirtuose, Mar 09 '17 at 07:11
@Sterkhov you need to make new file called as Manifest.mf and specify there your path to main class. Since, it is maven project 1) make manifest.mf file with args 2)mvn package 3) make jar as mentioned here wikihow.com/Create-JAR-File (step 3 already includes manifest creation) This is not 100% working — Malakai, Mar 09 '17 at 07:34
`false` should be set to true otherwise your .jar won't be able to find the dependencies copied by the maven-dependency-plugin. — Luciano van der Veekens, Mar 09 '17 at 08:08

score 0 · Answer 1 · answered Mar 09 '17 at 07:48

Build your jar with this plugin and specify the main class, this will add the correct META-INF in your generated jar.

 <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-shade-plugin</artifactId>
                <version>3.0.0</version>
                <executions>
                    <execution>
                        <phase>package</phase>
                        <goals>
                            <goal>shade</goal>
                        </goals>
                        <configuration>
                            <transformers>
                                <transformer
                                        implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
                                    <manifestEntries>
                                        <Main-Class>com.barclaycard.blackboxtester.Application</Main-Class>
                                        <Build-Number>123</Build-Number>
                                    </manifestEntries>
                                </transformer>
                            </transformers>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

score 0 · Answer 2 · answered Mar 10 '17 at 02:36

Your setup is similar to how I do it except you need to change this parameter in your POM file to be a value of "true".

<addClasspath>true</addClasspath>

Without it you would have to include dependencies on the command line and you are not. Java won't find jars just because they are in a directory. This command will add a "classpath" in the MANIFEST.MF file withing the JAR.

The generated MANIFEST.MF file would contain a line something like this (taken from one of my opensource projects). Your jar dependencies would of course be different.

Class-Path: calendar-2.2.3.jar algebrain-2.2.3.jar commons-codec-1.9.j
 ar argument-4.3.8.jar slf4j-api-1.7.13.jar slf4j-log4j12-1.7.13.jar l
 og4j-1.2.17.jar

score 0 · Answer 3 · answered Sep 29 '17 at 14:36

0

The file structure while creating any mavenized project should src/main/java and package should be include in class file other wise it will throw error Could not find or load main class

answered Sep 29 '17 at 14:36

Amit

7
5

Maven build Error: Could not find or load main class

3 Answers3