Added application layer and blockchain implementation

src/main/java/com/rviewer/skeletons/application/exception/ControllerExceptionHandler.java

@@ -0,0 +1,32 @@
+package com.rviewer.skeletons.application.exception;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.http.ResponseEntity;
+import org.springframework.http.converter.HttpMessageNotReadableException;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ControllerAdvice;
+import org.springframework.web.bind.annotation.ExceptionHandler;
+import org.springframework.web.bind.annotation.ResponseStatus;
+
+@ControllerAdvice
+public class ControllerExceptionHandler {
+
+    public static final String INVALID_BODY = "Invalid body provided, check the payload.";
+
+    @ExceptionHandler(CartNotFoundException.class)
+    public ResponseEntity<Object> handleCartNotFound(CartNotFoundException e) {
+        return new ResponseEntity<>(e.getMessage(), HttpStatus.NOT_FOUND);
+    }
+
+    @ExceptionHandler(CartAlreadyExistsException.class)
+    public ResponseEntity<Object> handleCartAlreadyExists(CartAlreadyExistsException e) {
+        return new ResponseEntity<>(e.getMessage(), HttpStatus.CONFLICT);
+    }
+
+    @ExceptionHandler({MethodArgumentNotValidException.class, HttpMessageNotReadableException.class})
+    @ResponseStatus(HttpStatus.BAD_REQUEST)
+    public ResponseEntity<Object> handleInvalidBody() {
+        return new ResponseEntity<>(INVALID_BODY, HttpStatus.BAD_REQUEST);
+    }
+
+}