How do I tell Spring Boot which main class to use for the executable jar?

Question

Add your start class in your pom:

<properties>
    <!-- The main class to start by executing java -jar -->
    <start-class>com.mycorp.starter.HelloWorldApplication</start-class>
</properties>

or

<build>
<plugins>
    <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>             
        <configuration>    
            <mainClass>com.mycorp.starter.HelloWorldApplication</mainClass>
        </configuration>
    </plugin>
</plugins>
</build>

For those using Gradle (instead of Maven) :

springBoot {
    mainClass = "com.example.Main"
}

If you do NOT use the spring-boot-starter-parent pom, then from the Spring documentation:

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>1.1.3.RELEASE</version>
    <configuration>
        <mainClass>my.package.MyStartClass</mainClass>
        <layout>ZIP</layout>
    </configuration>
    <executions>
        <execution>
            <goals>
                <goal>repackage</goal>
            </goals>
        </execution>
    </executions>
</plugin>

For those using Gradle (instead of Maven), referencing here:

The main class can also be configured explicitly using the task’s mainClassName property:

bootJar {
    mainClass = 'com.example.ExampleApplication'
}

Alternatively, the main class name can be configured project-wide using the mainClassName property of the Spring Boot DSL:

springBoot {
    mainClass = 'com.example.ExampleApplication'
}

If you're using spring-boot-starter-parent in your pom, you simply add the following to your pom:

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

Then do your mvn package.

See this Spring docs page.

A very important aspect here is to mention that the directory structure has to be src/main/java/nameofyourpackage

I tried the following code in pom.xml and it worked for me

<build>
<plugins>
    <plugin>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-maven-plugin</artifactId>
        <configuration>
            <mainClass>myPackage.HelloWorld</mainClass> 
        </configuration>
    </plugin>
    <plugin>
        <artifactId>maven-compiler-plugin</artifactId>
        <configuration>
            <fork>true</fork>
            <executable>D:\jdk1.8\bin\javaw.exe</executable>
        </configuration>
    </plugin>
</plugins>