Add validation to NewRestaurantDTO and handle exceptions

Added @notblank validation to the NewRestaurantDTO fields and included the spring-boot-starter-validation dependency in pom.xml. Created new classes ExceptionResponse and ExceptionResponseMessage to handle validation errors. The GlobalExceptionHandler class was also introduced to capture MethodArgumentNotValidException and provide appropriate response messages.

backend/pom.xml

@@ -28,14 +28,16 @@
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-web</artifactId>
 		</dependency>
+		<dependency>
+			<groupId>org.springframework.boot</groupId>
+			<artifactId>spring-boot-starter-validation</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>de.flapdoodle.embed</groupId>
 			<artifactId>de.flapdoodle.embed.mongo.spring3x</artifactId>
 			<version>4.13.0</version>
 			<scope>test</scope>
 		</dependency>
-
-
 		<dependency>
 			<groupId>org.springframework.boot</groupId>
 			<artifactId>spring-boot-starter-test</artifactId>

backend/src/main/java/com/neuefische/team2/backend/exceptions/GlobalExceptionHandler.java

@@ -0,0 +1,28 @@
+package com.neuefische.team2.backend.exceptions;
+
+import com.neuefische.team2.backend.exceptions.domain.ExceptionResponse;
+import com.neuefische.team2.backend.exceptions.domain.ExceptionResponseMessage;
+import org.springframework.http.HttpStatus;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.ResponseStatus;
+import org.springframework.web.bind.annotation.RestControllerAdvice;
+
+import java.util.List;
+
+
+@RestControllerAdvice
+public class GlobalExceptionHandler {
+
+    @ExceptionHandler(MethodArgumentNotValidException.class)
+    @ResponseStatus(HttpStatus.BAD_REQUEST)
+    public ExceptionResponse handleMethodArgumentNotValidException(MethodArgumentNotValidException exception) {
+
+        List<ExceptionResponseMessage> errors = exception.getFieldErrors()
+                .stream()
+                .map(error -> new ExceptionResponseMessage(error.getField(), error.getDefaultMessage()))
+                .toList();
+
+        return new ExceptionResponse(errors);
+    }
+}

backend/src/main/java/com/neuefische/team2/backend/exceptions/domain/ExceptionResponse.java

@@ -0,0 +1,8 @@
+package com.neuefische.team2.backend.exceptions.domain;
+
+import java.util.List;
+
+public record ExceptionResponse(
+        List<ExceptionResponseMessage> errors
+) {
+}

backend/src/main/java/com/neuefische/team2/backend/exceptions/domain/ExceptionResponseMessage.java

@@ -0,0 +1,7 @@
+package com.neuefische.team2.backend.exceptions.domain;
+
+public record ExceptionResponseMessage(
+        String field,
+        String message
+) {
+}

backend/src/main/java/com/neuefische/team2/backend/restaurant/RestaurantController.java

@@ -2,6 +2,7 @@
 
 import com.neuefische.team2.backend.restaurant.domain.NewRestaurantDTO;
 import com.neuefische.team2.backend.restaurant.domain.Restaurant;
+import jakarta.validation.Valid;
 import org.springframework.http.HttpStatus;
 import org.springframework.web.bind.annotation.*;
 
@@ -24,7 +25,7 @@ public List<Restaurant> getRestaurants() {
 
     @PostMapping
     @ResponseStatus(HttpStatus.CREATED)
-    public Restaurant addRestaurant(@RequestBody NewRestaurantDTO newRestaurantDTO) {
+    public Restaurant addRestaurant(@RequestBody @Valid NewRestaurantDTO newRestaurantDTO) {
         Restaurant restaurant = new Restaurant(null, newRestaurantDTO.title(), newRestaurantDTO.city());
         return restaurantService.addRestaurant(restaurant);
     }

backend/src/main/java/com/neuefische/team2/backend/restaurant/domain/NewRestaurantDTO.java

@@ -1,7 +1,11 @@
 package com.neuefische.team2.backend.restaurant.domain;
 
+import jakarta.validation.constraints.NotBlank;
+
 public record NewRestaurantDTO(
+        @NotBlank(message="Title must not be empty")
         String title,
+        @NotBlank(message="City must not be empty")
         String city
 ) {
 }