无法加载Procfile所指向的主类

myapp/
├── Procfile
├── src/
│   └── main/
│       └── java/
│           └── com/
│               └── example/
│                   └── Main.java
└── pom.xml

package com.example;

public class Main {
    public static void main(String[] args) {
        System.out.println("Hello, World!");
    }
}

web: java -jar target/myapp.jar

<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.example</groupId>
  <artifactId>myapp</artifactId>
  <version>1.0-SNAPSHOT</version>
  <build>
    <plugins>
      <plugin>
        <groupId>org.apache.maven.plugins</groupId>
        <artifactId>maven-jar-plugin</artifactId>
        <version>3.2.0</version>
        <configuration>
          <archive>
            <manifest>
              <mainClass>com.example.Main</mainClass>
            </manifest>
          </archive>
        </configuration>
      </plugin>
    </plugins>
  </build>
</project>