fix: correct 404 not found responses and few test changes

src/main/java/org/springframework/samples/petclinic/rest/advice/ExceptionControllerAdvice.java

@@ -16,8 +16,7 @@
 
 package org.springframework.samples.petclinic.rest.advice;
 
-import com.fasterxml.jackson.core.JsonProcessingException;
-import com.fasterxml.jackson.databind.ObjectMapper;
+import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
@@ -33,23 +32,41 @@
 import static org.springframework.http.HttpStatus.BAD_REQUEST;
 
 /**
+ * Global Exception handler for REST controllers.
+ * <p>
+ * This class handles exceptions thrown by REST controllers and returns
+ * appropriate HTTP responses to the client.
+ *
  * @author Vitaliy Fedoriv
+ * @author Alexander Dudkin
  */
-
 @ControllerAdvice
 public class ExceptionControllerAdvice {
 
-    @ExceptionHandler(Exception.class)
-    public ResponseEntity<String> exception(Exception e) {
-        ObjectMapper mapper = new ObjectMapper();
-        ErrorInfo errorInfo = new ErrorInfo(e);
-        String respJSONstring = "{}";
-        try {
-            respJSONstring = mapper.writeValueAsString(errorInfo);
-        } catch (JsonProcessingException e1) {
-            e1.printStackTrace();
+    /**
+     * Record for storing error information.
+     * <p>
+     * This record encapsulates the class name and message of the exception.
+     *
+     * @param className The name of the exception class
+     * @param exMessage The message of the exception
+     */
+    private record ErrorInfo(String className, String exMessage) {
+        public ErrorInfo(Exception ex) {
+            this(ex.getClass().getName(), ex.getLocalizedMessage());
         }
-        return ResponseEntity.badRequest().body(respJSONstring);
+    }
+
+    /**
+     * Handles all general exceptions by returning a 500 Internal Server Error status with error details.
+     *
+     * @param e The exception to be handled
+     * @return A {@link ResponseEntity} containing the error information and a 500 Internal Server Error status
+     */
+    @ExceptionHandler(Exception.class)
+    public ResponseEntity<ErrorInfo> handleGeneralException(Exception e) {
+        ErrorInfo info = new ErrorInfo(e);
+        return ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR).body(info);
     }
 
     /**
@@ -73,13 +90,38 @@ public ResponseEntity<Void> handleMethodArgumentNotValidException(MethodArgument
         return new ResponseEntity<>(headers, HttpStatus.BAD_REQUEST);
     }
 
-    private class ErrorInfo {
-        public final String className;
-        public final String exMessage;
+    /**
+     * Handles {@link DataIntegrityViolationException} which typically indicates database constraint violations.
+     * This method returns a 404 Not Found status if an entity does not exist.
+     *
+     * @param ex The {@link DataIntegrityViolationException} to be handled
+     * @return A {@link ResponseEntity} containing the error information and a 404 Not Found status
+     */
+    @ExceptionHandler(DataIntegrityViolationException.class)
+    @ResponseStatus(code = HttpStatus.NOT_FOUND)
+    @ResponseBody
+    public ResponseEntity<ErrorInfo> handleDataIntegrityViolationException(DataIntegrityViolationException ex) {
+        ErrorInfo errorInfo = new ErrorInfo(ex);
+        return ResponseEntity.status(HttpStatus.NOT_FOUND).body(errorInfo);
+    }
 
-        public ErrorInfo(Exception ex) {
-            this.className = ex.getClass().getName();
-            this.exMessage = ex.getLocalizedMessage();
+    /**
+     * Handles exception thrown by Bean Validation on controller methods parameters
+     *
+     * @param ex The thrown exception
+     * @return an empty response entity
+     */
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    @ResponseStatus(BAD_REQUEST)
+    @ResponseBody
+    public ResponseEntity<ErrorInfo> handleMethodArgumentNotValidException(MethodArgumentNotValidException ex) {
+        BindingErrorsResponse errors = new BindingErrorsResponse();
+        BindingResult bindingResult = ex.getBindingResult();
+        if (bindingResult.hasErrors()) {
+            errors.addAllErrors(bindingResult);
+            return ResponseEntity.badRequest().body(new ErrorInfo("MethodArgumentNotValidException", "Validation failed"));
         }
+        return ResponseEntity.badRequest().build();
     }
+
 }

src/test/java/org/springframework/samples/petclinic/rest/controller/PetRestControllerTests.java

@@ -241,7 +241,8 @@ void testAddPetError() throws Exception {
         String newPetAsJSON = mapper.writeValueAsString(newPet);
         given(this.clinicService.findPetById(999)).willReturn(null);
         this.mockMvc.perform(post("/api/pets")
-                .content(new String()).accept(MediaType.APPLICATION_JSON_VALUE).contentType(MediaType.APPLICATION_JSON_VALUE))
+                // empty content to force badRequest response
+                .content("{}").accept(MediaType.APPLICATION_JSON_VALUE).contentType(MediaType.APPLICATION_JSON_VALUE))
             .andExpect(status().isBadRequest());
     }
 }

src/test/java/org/springframework/samples/petclinic/rest/controller/UserRestControllerTests.java

@@ -64,7 +64,7 @@ void testCreateUserSuccess() throws Exception {
     void testCreateUserError() throws Exception {
         User user = new User();
         user.setUsername("username");
-        user.setPassword("password");
+        user.setPassword(""); // empty password to force badRequest Response
         user.setEnabled(true);
         ObjectMapper mapper = new ObjectMapper();
         String newVetAsJSON = mapper.writeValueAsString(userMapper.toUserDto(user));