SpringBoot: Unable to find a single main class from the following candidates

Question

I\'ve generated a Spring Boot web application using Spring Initializer, embedded Tomcat, Thymeleaf template engine.Technologies used: Spring Boot 1.4.2.RELEASE, Spring 4.3.4

Answer 1

If you have a Spring Boot Application generally there is only one main class that has @SpringBootApplication , If you add another main method in the application some where , the gradle build process gets confused . So add the following at the root level of your build.gradle file

apply plugin: 'application'
mainClassName = 'packageNameAfter.srcMainJavaFolder.YourClassName'

Answer 2

I had the same error. I had renamed my Application class containing main from foo.java to bar.java, cleaned and updated. So I only ever had one main.

The error went away when I deleted the old generated class, foo.class under the target folder.

Answer 3

[ERROR] Failed to execute goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage (default) on project book: Execution default of goal org.springframework.boot:spring-boot-maven-plugin:1.5.2.RELEASE:repackage failed: Unable to find a single main class from the following candidates [com.tdk.BookApplication, com.tdk.BookApplicationWar] 

One possible reason to getting following error is more than one main methods in your code, Spring boot allow only one main method across all class in same project.

Answer 4

From the command line you can use

... -Dstart-class=com.your.package.application.BookApplication

Answer 5

If you have more than one main class, you need to explicitly configure the main class in each profile:

<profiles>
    <profile>
        <id>profile1</id>
        <properties>
          <spring.boot.mainclass>com.SomeClass</spring.boot.mainclass>
        </properties>
    </profile>
    <profile>
        <id>profile2</id>
        <properties>
          <spring.boot.mainclass>com.SomeOtherClass</spring.boot.mainclass>
        </properties>
    </profile>
</profiles>

...

<plugin>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-maven-plugin</artifactId>
    <version>1.5.2.RELEASE</version>
    <executions>
      <execution>
        <goals>
          <goal>repackage</goal>
        </goals>
        <configuration>
          <mainClass>${spring.boot.mainclass}</mainClass>
        </configuration>
      </execution>
    </executions>
    ...
</plugin>

See spring-boot:repackage

Answer 6

Check your application if you have multiple classes with public static void main(String[] args). Remove the one that you do not need. Specially if you generate the project with https://start.spring.io/ it comes with a class with main method in it.

If you do need all of the classes with main method just explicitly mention which one would to be boos-trapped up on application start up by mentioning it in the pom.