working out how to handle exception based errors in a 'nice' way

Java/Spring/activitypubbot/src/main/java/dev/activitypub/activitypubbot/BotController.java

@@ -5,7 +5,11 @@ import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PostMapping;
 import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.ModelAttribute;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.web.servlet.ModelAndView;
+import org.springframework.http.HttpStatus;
 import org.springframework.ui.Model;
 import java.util.List;
 import lombok.extern.slf4j.Slf4j;
@@ -21,6 +25,17 @@ public class BotController {
     @Autowired
     private BotService botServ;
 
+    /**
+     * Send a 404 page for bots if someone tries to access a bot that doesn't exist.
+     */
+    @ExceptionHandler(value = BotNotFoundByUsernameException.class)
+    @ResponseStatus(HttpStatus.NOT_FOUND)
+    public ModelAndView handleBotNotFoundByUsernameException(BotNotFoundByUsernameException ex) {
+        ModelAndView mav = new ModelAndView("user_not_found");
+        mav.addObject("message", ex.getLocalizedMessage()); 
+        return mav;
+    }
+
     @GetMapping("/viewbot")
     public String listAll(Model model) {
         log.info("BotController::viewbot");

Java/Spring/activitypubbot/src/main/java/dev/activitypub/activitypubbot/BotService.java

@@ -31,7 +31,7 @@ public class BotService {
     }
 
     public Bot getBotByUsername( String username ) {
-        return repo.findByUsername( username ).get();
+        return repo.findByUsername( username ).orElseThrow(() -> new BotNotFoundByUsernameException(username));
     }
 
 

Java/Spring/activitypubbot/src/main/java/dev/activitypub/activitypubbot/RestHandler.java

@@ -7,7 +7,6 @@ import org.springframework.web.bind.annotation.PathVariable;
 import org.springframework.web.bind.annotation.RequestParam;
 import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.beans.factory.annotation.Autowired;
-import org.springframework.web.server.ResponseStatusException;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.thymeleaf.context.Context;