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>

Answer 1

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>

Answer 2

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

Answer 3

创建任何 mavenized 项目时的文件结构应该src/main/java和包应该包含在类文件中，否则它将抛出错误无法找到或加载主类