fix: centralise error handling in GlobalExceptionHandler, add SLF4J logging, remove HTTP 417 and e.printStackTrace()

- Expand GlobalExceptionHandler with handlers for ResourceNotFoundException (404),
  UsernameAlreadyExistsException (409), ResponseStatusException (pass-through),
  RuntimeException (500), and generic Exception (500); add SLF4J logging
- Remove all bare try/catch blocks and e.printStackTrace() calls from
  ExpenseListController; add SLF4J logger field
- Add test: create_returns500_onUnexpectedServiceError

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/main/java/de/zendric/app/xpensely_server/controller/ExpenseListController.java

@@ -5,6 +5,8 @@ import java.util.List;
 import java.util.Optional;
 
 import jakarta.validation.Valid;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.security.core.Authentication;
@@ -21,6 +23,8 @@ import de.zendric.app.xpensely_server.services.UserService;
 @RequestMapping("/api/expenselist")
 public class ExpenseListController {
 
+    private static final Logger log = LoggerFactory.getLogger(ExpenseListController.class);
+
     private final ExpenseListService expenseListService;
     private final UserService userService;
     private final CategoryService categoryService;
@@ -56,7 +60,6 @@ public class ExpenseListController {
     @PostMapping("/create")
     public ResponseEntity<ExpenseList> create(@RequestBody ExpenseList expenseList,
             Authentication authentication) {
-        try {
         AppUser authenticatedUser = authenticatedUserResolver.resolveCurrentUser(authentication);
         expenseList.setOwner(authenticatedUser);
         XpenselyStandardCategories standardCategories = categoryService.getDefaultCategories();
@@ -64,12 +67,6 @@ public class ExpenseListController {
         expenseList.setSharedWith(null);
         ExpenseList savedItem = expenseListService.createList(expenseList);
         return new ResponseEntity<>(savedItem, HttpStatus.CREATED);
-        } catch (ResponseStatusException e) {
-            throw e;
-        } catch (Exception e) {
-            e.printStackTrace();
-            return new ResponseEntity<>(null, HttpStatus.EXPECTATION_FAILED);
-        }
     }
 
     @DeleteMapping("{id}")
@@ -79,12 +76,8 @@ public class ExpenseListController {
         if (listOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertOwner(user, listOpt.get());
-        try {
         expenseListService.deleteById(id);
         return new ResponseEntity<>(HttpStatus.NO_CONTENT);
-        } catch (Exception e) {
-            return new ResponseEntity<>(HttpStatus.EXPECTATION_FAILED);
-        }
     }
 
     @PostMapping("/{id}/add")
@@ -97,14 +90,10 @@ public class ExpenseListController {
         if (listOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertMember(user, listOpt.get());
-        try {
         AppUser expenseOwner = userService.getUserByName(expenseInput.getOwner());
         Expense expense = expenseInput.convertToExpense(expenseOwner.getId());
         Expense addedExpense = expenseListService.addExpenseToList(expenseListId, expense);
         return new ResponseEntity<>(addedExpense, HttpStatus.CREATED);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.INTERNAL_SERVER_ERROR);
-        }
     }
 
     @PutMapping("/{id}/update")
@@ -117,14 +106,10 @@ public class ExpenseListController {
         if (expenseListOpt.isEmpty())
             return new ResponseEntity<>(null, HttpStatus.NOT_FOUND);
         assertMember(user, expenseListOpt.get());
-        try {
         AppUser expenseOwner = userService.getUserByName(expenseChangeRequest.getOwnerName());
         Expense expense = expenseChangeRequest.convertToExpense(expenseOwner.getId(), expenseListOpt.get());
         Expense updatedExpense = expenseListService.updateExpense(expenseListId, expense);
         return new ResponseEntity<>(updatedExpense, HttpStatus.OK);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.BAD_REQUEST);
-        }
     }
 
     @DeleteMapping("/{id}/delete")
@@ -137,12 +122,8 @@ public class ExpenseListController {
         if (listOpt.isEmpty())
             return new ResponseEntity<>(HttpStatus.NOT_FOUND);
         assertMember(user, listOpt.get());
-        try {
         expenseListService.deleteExpenseFromList(expenseListId, expenseId);
         return new ResponseEntity<>(HttpStatus.NO_CONTENT);
-        } catch (Exception e) {
-            return new ResponseEntity<>(null, HttpStatus.EXPECTATION_FAILED);
-        }
     }
 
     @PostMapping("/{listId}/invite")

src/main/java/de/zendric/app/xpensely_server/controller/GlobalExceptionHandler.java

@@ -1,11 +1,16 @@
 package de.zendric.app.xpensely_server.controller;
 
+import de.zendric.app.xpensely_server.model.Exception.ResourceNotFoundException;
+import de.zendric.app.xpensely_server.model.Exception.UsernameAlreadyExistsException;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
 import org.springframework.validation.FieldError;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ExceptionHandler;
 import org.springframework.web.bind.annotation.RestControllerAdvice;
+import org.springframework.web.server.ResponseStatusException;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -13,6 +18,8 @@ import java.util.Map;
 @RestControllerAdvice
 public class GlobalExceptionHandler {
 
+    private static final Logger log = LoggerFactory.getLogger(GlobalExceptionHandler.class);
+
     @ExceptionHandler(MethodArgumentNotValidException.class)
     public ResponseEntity<Map<String, String>> handleValidationErrors(MethodArgumentNotValidException ex) {
         Map<String, String> errors = new HashMap<>();
@@ -27,4 +34,36 @@ public class GlobalExceptionHandler {
         return ResponseEntity.status(HttpStatus.BAD_REQUEST)
                 .body(Map.of("error", ex.getMessage()));
     }
+
+    @ExceptionHandler(ResourceNotFoundException.class)
+    public ResponseEntity<Map<String, String>> handleNotFound(ResourceNotFoundException ex) {
+        return ResponseEntity.status(HttpStatus.NOT_FOUND)
+                .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(UsernameAlreadyExistsException.class)
+    public ResponseEntity<Map<String, String>> handleUsernameConflict(UsernameAlreadyExistsException ex) {
+        return ResponseEntity.status(HttpStatus.CONFLICT)
+                .body(Map.of("error", ex.getMessage()));
+    }
+
+    @ExceptionHandler(ResponseStatusException.class)
+    public ResponseEntity<Map<String, String>> handleResponseStatus(ResponseStatusException ex) {
+        return ResponseEntity.status(ex.getStatusCode())
+                .body(Map.of("error", ex.getReason() != null ? ex.getReason() : ex.getMessage()));
+    }
+
+    @ExceptionHandler(RuntimeException.class)
+    public ResponseEntity<Map<String, String>> handleRuntime(RuntimeException ex) {
+        log.error("Unhandled runtime exception", ex);
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                .body(Map.of("error", "An unexpected error occurred"));
+    }
+
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<Map<String, String>> handleGeneric(Exception ex) {
+        log.error("Unhandled exception", ex);
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR)
+                .body(Map.of("error", "An unexpected error occurred"));
+    }
 }

src/test/java/de/zendric/app/xpensely_Server/controller/ExpenseListControllerTest.java

@@ -132,4 +132,17 @@ class ExpenseListControllerTest {
         mockMvc.perform(get("/api/expenselist/mine"))
                 .andExpect(status().isOk());
     }
+
+    @Test
+    void create_returns500_onUnexpectedServiceError() throws Exception {
+        AppUser user = new AppUser();
+        user.setId(1L);
+        when(authenticatedUserResolver.resolveCurrentUser(any())).thenReturn(user);
+        when(categoryService.getDefaultCategories()).thenThrow(new RuntimeException("db down"));
+
+        mockMvc.perform(post("/api/expenselist/create")
+                        .contentType(MediaType.APPLICATION_JSON)
+                        .content("{\"name\":\"Groceries\"}"))
+                .andExpect(status().isInternalServerError());
+    }
 }