Unable to find a suitable main class, please add a 'mainClass' property - spring

Question

I totally understand this error message meaning, but how to fix it?
Intellij doesn't allow me to click on the main application class.
org.springframework.boot:spring-boot-maven-plugin:2.1.7.RELEASE:run (default-cli) on project XprojApplication: Unable to find a suitable main class, please add a 'mainClass' property -> [Help 1]
pom.xml
<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.1.7.RELEASE</version>
<relativePath/> <!-- lookup parent from repository -->
</parent>
<groupId>dev.house</groupId>
<artifactId>xproj</artifactId>
<version>0.0.1-SNAPSHOT</version>
<name>15house</name>
<description>Demo project for Spring Boot</description>
<properties>
<java.version>1.8</java.version>
</properties>
<packaging>war</packaging>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
<exclusions>
<exclusion>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
</exclusion>
</exclusions>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-tomcat</artifactId>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>org.apache.tomcat</groupId>
<artifactId>tomcat-servlet-api</artifactId>
<version>8.0.36</version>
<scope>provided</scope>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-test</artifactId>
<scope>test</scope>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-databind</artifactId>
<version>2.9.4</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-core</artifactId>
<version>2.9.4</version>
</dependency>
<dependency>
<groupId>com.fasterxml.jackson.core</groupId>
<artifactId>jackson-annotations</artifactId>
<version>2.9.4</version>
</dependency>
</dependencies>
<build>
<plugins>
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
</plugin>
<plugin>
<artifactId>maven-assembly-plugin</artifactId>
<executions>
<execution>
<phase>package</phase>
<goals>
<goal>single</goal>
</goals>
</execution>
</executions>
<configuration>
<!-- <archive>-->
<!-- <manifest>-->
<!-- <addClasspath>true</addClasspath>-->
<!-- <mainClass>dev.house.XprojApplication</mainClass>-->
<!-- </manifest>-->
<!-- </archive>-->
<descriptorRefs>
<descriptorRef>jar-with-dependencies</descriptorRef>
</descriptorRefs>
</configuration>
</plugin>
</plugins>
<directory>/Users/poc/workspace/tw-real-estate-service-manager/webapps/15house</directory>
<finalName>15house</finalName>
</build>
</project>

Answer 1

It does not seem that your directories are marked properly.
Since you're using Maven, I assume you have the following structure.
Please ensure to mark the java directory as Sources Root by right-clicking on the folder and following the Mark Directory as submenu. You might want to do the same for the resources directory, marking it as Resources Root.

Answer 2

If you want bootable jar for spring boot, you can simply use below configuration in your pom.xml, you don't need maven-assembly-plugin
<plugin>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-maven-plugin</artifactId>
<executions>
<execution>
<goals>
<goal>repackage</goal>
</goals>
<configuration>
<start-class>org.springframework.boot.loader.JarLauncher</start-class>
</configuration>
</execution>
</executions>
</plugin>