@Restcontrolleradvice **
A convenience annotation that combines @ControllerAdvice and @ResponseBody. It is designed for RESTful APIs where the return value of an exception handler is automatically serialized into the response body (typically as JSON or XML) instead of being resolved as a view.
**@ExceptionHandler
We can use @ExceptionHandler to annotate methods that Spring automatically invokes when the given exception occurs. We can specify the exception either with the annotation or by declaring it as a method parameter, which allows us to read out details from the exception object to handle it correctly. The method itself is handled as a Controller method.
EX:
@RestControllerAdvice
public class ExceptionController {
@ExceptionHandler(NullPointerException.class)
public String hanleNullPointerException(NullPointerException ex){
return "Error: "+ex.getMessage();
}
@ExceptionHandler(MethodArgumentNotValidException.class)
public String hanleIllegalArgumentException(MethodArgumentNotValidException ex){
return "Error: "+ex.getMessage();
}
}
@valid:
It informs controller about the presence of @ExceptionHandler.
When an exception occurs,Spring container redirects the flow to corresponding Exception handler method
@PostMapping("/SaveBookDetails")
public String SaveBookDetails(@RequestBody @valid BookDetails bookDetails) {
log.info("entering ProcessBookDetailsController");
String ValueFromService=bookService.SaveBookDetails(bookDetails);
log.info("leaving ProcessBookDetailsController");
return ValueFromService;
}
To Enable validations in coding we have Spring Boot validation dependency.
For Spring Boot applications, the standard dependency for enabling Bean Validation is spring-boot-starter-validation. This starter provides the Jakarta Bean Validation API and Hibernate Validator as the default implementation.
Enabling Validation: Once the dependency is added, you must use annotations such as @valid or @Validated on your controller method parameters (e.g., @RequestBody) to trigger the validation process.
Standard Annotations: The dependency supports standard JSR-380 annotations including @NotNull, @notblank, @Size, @min, @max, and @Email.
Historical Note: Starting with Spring Boot 2.3, the validation starter is no longer included by default in spring-boot-starter-web or spring-boot-starter-webflux. You must add it explicitly to your project.
Error Handling: When validation fails, Spring Boot typically throws a MethodArgumentNotValidException, which can be captured using a Global Exception Handler with @ControllerAdvice.
pom.xml
Dependency Configurations
org.springframework.boot
spring-boot-starter-validation
org.springframework.boot
spring-boot-starter-validation-test
test
Code:
package LiBrary;
import jakarta.validation.constraints.*;
public class BookDetails {
@NotEmpty
String bookName;
@NotNull
@Positive
@Min(0)
@Max(50)
int bookId;
double price;
@NotBlank
@NotEmpty
String authorName;
String Genre;
@Email
String email;
public String getEmail() {
return email;
}
public void setEmail(String email) {
this.email = email;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public String getBookName() {
return bookName;
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public int getBookId() {
return bookId;
}
public void setBookId(int bookId) {
this.bookId = bookId;
}
public String getGenre() {
return Genre;
}
public void setGenre(String genre) {
Genre = genre;
}
public String getAuthorName() {
return authorName;
}
public void setAuthorName(String authorName) {
this.authorName = authorName;
}
}
Setting default error message for valid annotations:
@NotEmpty(message="bookname cannot be blank")
String bookName;
@NotNull(message="Book id cannot be null")
@Positive(message="Book Id must be +ve")
@Min(0)
@Max(50)
int bookId;
double price;
@NotBlank(message="author name cannot be blank")
@NotEmpty(message="author name cannot be empty")
String authorName;
String Genre;
@Email(message="Not a valid email address")
String email;
error message:
arguments [org.springframework.context.support.DefaultMessageSourceResolvable: codes [bookDetails.bookId,bookId]; arguments []; default message [bookId]]; default message [Book Id must be +ve]] [Field error in object 'bookDetails' on field 'authorName': rejected value [ ]; codes [NotBlank.bookDetails.authorName,NotBlank.authorName,NotBlank.java.lang.String,NotBlank]; arguments [org.springframework.context.support.DefaultMessageSourceResolvable:
ResponseEntity:
ResponseEntity is a class in the Spring Framework used to represent the entire HTTP response. Unlike simply returning an object, it allows developers to fully configure the status code, headers, and response body sent back to the client.
It can be any objectlike List, Map or user define class
1.public class ResponseEntity extends HttpEntity
- Extension of HttpEntity that adds an HttpStatusCode status code. Used in RestTemplate as well as in @Controller methods. 3.In RestTemplate, this class is returned by getForEntity() and exchange(): Snippet 1: ResponseEntity entity = template.getForEntity("https://example.com", String.class); String body = entity.getBody(); MediaType contentType = entity.getHeaders().getContentType(); HttpStatus statusCode = entity.getStatusCode(); Snippet 2 public ResponseEntity hanleIllegalArgumentException(MethodArgumentNotValidException ex){ Map errors=new HashMap(); //Code Snippet 1 - displays only key error message ex.getBindingResult().getFieldErrors().forEach(Error->{ errors.put(Error.getField(),Error.getDefaultMessage()); }); return new ResponseEntity("validation error "+errors , HttpStatusCode.valueOf(400)); //Code Snippet 2 - displays all error with vast data // return new ResponseEntity("validation error "+ex.getMessage() , HttpStatusCode.valueOf(400)); } output: validation error {authorName=author name cannot be blank, bookName=bookname cannot be blank, email=Not a valid email address, bookId=must be less than or equal to 50}
In above snippet we returned a map. we can also return a class
References:
