In my case i have declared swagger @Bean in 2 different class. Once i removed from one class it resolved.

@Configuration 
@EnableSwagger2 
public class EnrollmentSecureConfig {
@Bean //------> 1st time
public Docket api() {}
}

@Configuration
@EnableSwagger2
public class EnrollmentSecureConfig {

@Bean //-----?2nd time
public Docket api() {}

}