Java web application deployment Heroku

I was doing some research last time about web services that could provide build & deployment of my Java web application. I found Heroku which seemed to be okay but I encountered some problem.

First of all, my application uses Spring MVC (not Spring Boot), I have manual java-based annotation configuration without web.xml at all. That's about setup. Now when it comes to mentioned error, I connected Heroku with my GitHub repository, then deployed it. Everything built fine with one single problem at the end which looks following:

2018-03-23T07:12:02.679019+00:00 app[web.1]: Error: Main method not found in class th.config.MyWebAppInitializer, please define the main method as:
2018-03-23T07:12:02.679037+00:00 app[web.1]: public static void main(String[] args)
2018-03-23T07:12:02.679150+00:00 app[web.1]: or a JavaFX application class must extend javafx.application.Application

Apparently Heroku environment requires a class that contains main method, which does not exist in my application, at least not in my own code, but probably somewhere in class that runs servlets, like ServletInitializer or something like that. I tried to use flag <skipMain>true</skipMain> flag in order to skip this but without any luck.

Here I include my pom.xml file:

<?xml version="1.0" encoding="UTF-8"?>
....
<modelVersion>4.0.0</modelVersion>
<packaging>war</packaging>
<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.7.0</version>
            <configuration>
                <skipMain>true</skipMain>
                <source>1.8</source>
                <target>1.8</target>
            </configuration>
            <executions>
                <execution>
                    <id>default-war</id>
                    <phase>prepare-package</phase>
                    <configuration>
                        <skipMain>true</skipMain>
                        <failOnMissingWebXml>false</failOnMissingWebXml>
                    </configuration>
                </execution>
            </executions>
        </plugin>
        <plugin>
            <artifactId>maven-war-plugin</artifactId>
            <version>3.2.0</version>
            <configuration>
                <failOnMissingWebXml>false</failOnMissingWebXml>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-dependency-plugin</artifactId>
            <version>3.0.2</version>
            <executions>
                <execution>
                    <phase>package</phase>
                    <goals><goal>copy-dependencies</goal></goals>
                    <configuration>
                        <artifactItems>
                            <artifactItem>
                                <groupId>com.github.jsimone</groupId>
                                <artifactId>webapp-runner</artifactId>
                                <version>7.0.22.3</version>
                                <destFileName>webapp-runner.jar</destFileName>
                            </artifactItem>
                        </artifactItems>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

<properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
</properties>


<groupId>webofficesuite</groupId>
<artifactId>webofficesuite</artifactId>
<version>1.0-SNAPSHOT</version>

<!-- SPRING COMPONENTS -->
<!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>4.3.13.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-core -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>4.3.13.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-web -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-web</artifactId>
        <version>4.3.13.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-webmvc -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>4.3.13.RELEASE</version>
    </dependency>

    <!-- SPRING SECURITY -->
    <!-- https://mvnrepository.com/artifact/org.springframework.security/spring-security-core -->
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-core</artifactId>
        <version>4.2.3.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework.security/spring-security-web -->
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-web</artifactId>
        <version>4.2.3.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework.security/spring-security-config -->
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-config</artifactId>
        <version>4.2.3.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework.security/spring-security-taglibs -->
    <dependency>
        <groupId>org.springframework.security</groupId>
        <artifactId>spring-security-taglibs</artifactId>
        <version>4.2.3.RELEASE</version>
    </dependency>


    <!-- Spring ORM -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-orm</artifactId>
        <version>4.3.7.RELEASE</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.springframework/spring-tx -->
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-tx</artifactId>
        <version>4.3.13.RELEASE</version>
    </dependency>


    <!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>6.0.6</version>
    </dependency>

    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-dbcp</artifactId>
        <version>7.0.55</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.apache.tomcat/tomcat-catalina -->
    <dependency>
        <groupId>org.apache.tomcat</groupId>
        <artifactId>tomcat-catalina</artifactId>
        <version>9.0.1</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>

    <!-- https://mvnrepository.com/artifact/jstl/jstl -->
    <dependency>
        <groupId>jstl</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>

    <dependency>
        <groupId>javax.servlet.jsp</groupId>
        <artifactId>jsp-api</artifactId>
        <version>2.1</version>
        <scope>provided</scope>
    </dependency>

    ...Other dependencies

</dependencies>

I would appreciate any help or guide that would allow me to successfully deploy my app. Additionally I tried other web service that is called OpenShift and I managed to deploy my application there, but I don't like that it is hardly possible to remotely connect to a mysql database, so I would prefer the Heroku solution. But if there are any other good web service hostings that you would recommend I am open for suggestions. The only requirement is that it doesn't cost ridiculously much money per month because it won't be huge application that require a lot of cores and memory.