How do I tell Spring Boot which main class to use for the executable jar?
JavaSpringMavenExecutable JarSpring BootJava Problem Overview
Execution default of goal
org.springframework.boot:spring-boot-maven-plugin:1.0.1.RELEASE:repackage
failed:
Unable to find a single main class from the following candidates
My project has more than one class with a main
method. How do I tell the Spring Boot Maven plugin which of the classes it should use as the main class?
Java Solutions
Solution 1 - Java
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>
Solution 2 - Java
For those using Gradle (instead of Maven) :
springBoot {
mainClass = "com.example.Main"
}
Solution 3 - Java
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>
Solution 4 - Java
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'
}
Solution 5 - Java
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.
A very important aspect here is to mention that the directory structure has to be src/main/java/nameofyourpackage
Solution 6 - Java
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>
Solution 7 - Java
Since Spring Boot 1.5, you can complete ignore the error-prone string literal in pom or build.gradle. The repackaging tool (via maven or gradle plugin) will pick the one annotated with @SpringBootApplication
for you. (Refer to this issue for detail: https://github.com/spring-projects/spring-boot/issues/6496 )
Solution 8 - Java
I had renamed my project and it was still finding the old Application
class on the build path. I removed it in the 'build' folder and all was fine.
Solution 9 - Java
Have seen this issue with Java 1.9 and SpringBoot 1.5.x, when main-class is not specified explicitly.
With Java 1.8, it is able to find main-class without explicit property and 'mvn package' works fine.
Solution 10 - Java
If you are using Grade, it is possible to apply the 'application' plugin rather than the 'java' plugin. This allows specifying the main class as below without using any Spring Boot Gradle plugin tasks.
plugins {
id 'org.springframework.boot' version '2.3.3.RELEASE'
id 'io.spring.dependency-management' version '1.0.10.RELEASE'
id 'application'
}
application {
mainClassName = 'com.example.ExampleApplication'
}
As a nice benefit, one is able to run the application using gradle run
with the classpath automatically configured by Gradle. The plugin also packages the application as a TAR and/or ZIP including operating system specific start scripts.