Error: Could not find or load main class in spring boot

Error: Could not find or load main class is a common error encountered in Spring Boot applications. This error occurs when the Java Virtual Machine (JVM) is unable to locate the main class specified in the command to run the application. In this blog post, we’ll go over the causes of this error in Spring Boot and how to resolve it.



Cause of the Error

  1. Incorrect main class name: The main class name specified in the SpringBootApplication annotation is incorrect.
  2. Missing dependencies: Required dependencies are not included in the classpath and are not being found by the JVM.
  3. Incorrect build configuration: The build configuration (e.g. pom.xml) is incorrect and is not including the required dependencies.
  4. Incorrect classpath: The classpath specified in the command to run the application is incorrect, leading to the JVM not finding the required class files.


How to Resolve the Error

  1. Verify the main class name: Make sure the main class name specified in the SpringBootApplication annotation matches the actual name of the class in the code.

Example:

@SpringBootApplication
public class MainClass {
  public static void main(String[] args) {
    SpringApplication.run(MainClass.class, args);
  }
}
  1. Add required dependencies: Ensure the required dependencies are included in the classpath and are being found by the JVM.

Example pom.xml:

<dependencies>
  <dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
  </dependency>
</dependencies>
  1. Verify build configuration: Make sure the build configuration (e.g. pom.xml) is correct and includes all required dependencies.

Example pom.xml:

<build>
  <plugins>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
    </plugin>
  </plugins>
</build>
  1. Check classpath: Verify the classpath specified in the command to run the application is correct.

Example:

$ mvn spring-boot:run


Conclusion

In conclusion, the Error: Could not find or load main class error is a common issue faced by Spring Boot developers. By understanding the causes of the error and following the steps outlined in this blog post, you can resolve this error and continue with your Spring Boot application development.



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