How to find the logged-in user in Spring Boot?

To find the logged-in user in a Spring Boot application, you can use the SecurityContextHolder class provided by Spring Security. Here are the steps to do so:

Import the necessary classes:
Import the SecurityContextHolder class from org.springframework.security.core.context.SecurityContextHolder.
Import the Authentication class from org.springframework.security.core.Authentication.
Retrieve the authentication object:
Use the getContext() method of SecurityContextHolder to get the current security context.
Use the getAuthentication() method of the security context to retrieve the authentication object.
Check if the authentication object is not null and the principal is an instance of UserDetails:
Use the != null condition to check if the authentication object is not null.
Use the instanceof operator to check if the principal object is an instance of UserDetails.
If the above condition is true, cast the principal object to UserDetails and perform further operations:
Use the getPrincipal() method of the authentication object to retrieve the principal object.
Cast the principal object to UserDetails or your custom user details implementation.
You can now access the logged-in user's information and perform any necessary operations.

Here's an example code snippet that demonstrates the above steps:

import org.springframework.security.core.Authentication;
import org.springframework.security.core.context.SecurityContextHolder;

// ...

Authentication authentication = SecurityContextHolder.getContext().getAuthentication();
if (authentication != null && authentication.getPrincipal() instanceof UserDetails) {
    UserDetails userDetails = (UserDetails) authentication.getPrincipal();
    // Access the logged-in user's information using the userDetails object
    String username = userDetails.getUsername();
    // ...
}

Please note that the above code assumes that you have already configured Spring Security in your Spring Boot application. The SecurityContextHolder class provides access to the security context, which holds the authentication information for the current user.

I hope this helps! Let me know if you have any further questions.