Hw add global exception handler

pom.xml

@@ -87,6 +87,11 @@
             <artifactId>liquibase-core</artifactId>
             <version>${liquibase.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.hibernate.validator</groupId>
+            <artifactId>hibernate-validator</artifactId>
+            <version>7.0.5.Final</version>
+        </dependency>
     </dependencies>
 
     <build>

src/main/java/project/bookstore/controller/BookController.java

@@ -1,5 +1,6 @@
 package project.bookstore.controller;
 
+import jakarta.validation.Valid;
 import java.util.List;
 import lombok.RequiredArgsConstructor;
 import org.springframework.web.bind.annotation.DeleteMapping;
@@ -34,13 +35,13 @@ public BookDto getBookById(@PathVariable Long id) {
     }
 
     @PostMapping
-    public BookDto createBook(@RequestBody CreateBookRequestDto requestDto) {
+    public BookDto createBook(@RequestBody @Valid CreateBookRequestDto requestDto) {
         return bookMapper.toDto(bookService.save(requestDto));
     }
 
     @PutMapping("/{id}")
     public BookDto updateBook(
-            @RequestBody CreateBookRequestDto requestDto,
+            @RequestBody @Valid CreateBookRequestDto requestDto,
             @PathVariable Long id
     ) {
         return bookService.updateBook(requestDto, id);

src/main/java/project/bookstore/dto/CreateBookRequestDto.java

@@ -1,15 +1,25 @@
 package project.bookstore.dto;
 
+import jakarta.validation.constraints.NotBlank;
+import jakarta.validation.constraints.NotNull;
+import jakarta.validation.constraints.PositiveOrZero;
 import java.math.BigDecimal;
 import lombok.Getter;
 import lombok.Setter;
+import project.bookstore.validation.Unique;
 
 @Getter
 @Setter
 public class CreateBookRequestDto {
+    @NotBlank
     private String title;
+    @NotBlank
     private String author;
+    @NotNull
+    @Unique
     private String isbn;
+    @NotNull
+    @PositiveOrZero
     private BigDecimal price;
     private String description;
     private String coverImage;

src/main/java/project/bookstore/exception/CustomGlobalExceptionHandler.java

@@ -0,0 +1,46 @@
+package project.bookstore.exception;
+
+import java.time.LocalDateTime;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import org.springframework.http.HttpHeaders;
+import org.springframework.http.HttpStatus;
+import org.springframework.http.HttpStatusCode;
+import org.springframework.http.ResponseEntity;
+import org.springframework.validation.FieldError;
+import org.springframework.validation.ObjectError;
+import org.springframework.web.bind.MethodArgumentNotValidException;
+import org.springframework.web.bind.annotation.ControllerAdvice;
+import org.springframework.web.context.request.WebRequest;
+import org.springframework.web.servlet.mvc.method.annotation.ResponseEntityExceptionHandler;
+
+@ControllerAdvice
+public class CustomGlobalExceptionHandler extends ResponseEntityExceptionHandler {
+
+    @Override
+    protected ResponseEntity<Object> handleMethodArgumentNotValid(
+            MethodArgumentNotValidException ex,
+            HttpHeaders headers,
+            HttpStatusCode status,
+            WebRequest request
+    ) {
+        Map<String, Object> body = new LinkedHashMap<>();
+        body.put("timestamp", LocalDateTime.now());
+        body.put("status", HttpStatus.BAD_REQUEST);
+        List<String> errors = ex.getBindingResult().getAllErrors().stream()
+                .map(this::getErrorMessage)
+                .toList();
+        body.put("error", errors);
+        return new ResponseEntity<>(body, headers, status);
+    }
+
+    private String getErrorMessage(ObjectError e) {
+        if (e instanceof FieldError) {
+            String fieldName = ((FieldError) e).getField();
+            String message = ((FieldError) e).getDefaultMessage();
+            return fieldName + ": " + message;
+        }
+        return e.getDefaultMessage();
+    }
+}

src/main/java/project/bookstore/repository/BookRepository.java

@@ -6,4 +6,6 @@
 
 public interface BookRepository extends JpaRepository<Book, Long>, JpaSpecificationExecutor<Book> {
 
+    boolean existsByIsbn(String isbn);
+
 }

src/main/java/project/bookstore/validation/Unique.java

@@ -0,0 +1,17 @@
+package project.bookstore.validation;
+
+import jakarta.validation.Constraint;
+import jakarta.validation.Payload;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Constraint(validatedBy = UniqueValidation.class)
+@Target({ElementType.FIELD})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Unique {
+    String message() default "This field is already exist!";
+    Class<?>[] groups() default {};
+    Class<? extends Payload>[] payload() default {};
+}

src/main/java/project/bookstore/validation/UniqueValidation.java

@@ -0,0 +1,16 @@
+package project.bookstore.validation;
+
+import jakarta.validation.ConstraintValidator;
+import jakarta.validation.ConstraintValidatorContext;
+import org.springframework.beans.factory.annotation.Autowired;
+import project.bookstore.repository.BookRepository;
+
+public class UniqueValidation implements ConstraintValidator<Unique, String> {
+    @Autowired
+    private BookRepository repository;
+
+    @Override
+    public boolean isValid(String value, ConstraintValidatorContext constraintValidatorContext) {
+        return !repository.existsByIsbn(value);
+    }
+}