Validate image if existing or not null only in spring boot?

Question

I'm trying to validate image in Spring boot with a custom messages and custom validator. Here is my file path for the validator files

I just need to know how to check first if the image file is existing or not null and then validate it.

I need to mention that my image can be null value, in this case, I should not do the validation.

Here is the example for more clarification:

I first created the annotation as follows:

import javax.validation.Constraint;
import javax.validation.Payload;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy = {ImageFileValidator.class})
public @interface ValidImage {
    String message() default "Invalid image file";

    Class<?>[] groups() default {};

    Class<? extends Payload>[] payload() default {};
}

I've created the validator as following:

import org.springframework.web.multipart.MultipartFile;

import javax.validation.ConstraintValidator;
import javax.validation.ConstraintValidatorContext;

public class ImageFileValidator implements ConstraintValidator<ValidImage, MultipartFile> {

    @Override
    public void initialize(ValidImage constraintAnnotation) {

    }

    @Override
    public boolean isValid(MultipartFile multipartFile, ConstraintValidatorContext context) {

        boolean result = true;

        String contentType = multipartFile.getContentType();
        if (!isSupportedContentType(contentType)) {
            context.disableDefaultConstraintViolation();
            context.buildConstraintViolationWithTemplate(
                    "Only PNG or JPG images are allowed.")
                   .addConstraintViolation();

            result = false;
        }

        return result;
    }

    private boolean isSupportedContentType(String contentType) {
        return contentType.equals("image/png")
                || contentType.equals("image/jpg")
                || contentType.equals("image/jpeg");
    }
}

Finally, applied the annotation as following:

public class CreateUserParameters {

    @ValidImage
    private MultipartFile image;
...
}

The code of the custom validator was here : File upload in Spring Boot: Uploading, validation, and exception handling by Wim Deblauwe in the last comment.

I need to add a some code to the annotation that if the image is null, should not validate and just skip. — Ahmed Mohamed, Sep 15 '21 at 00:18
I'm uploading a file and that file gets validated by the above code. But when the value is null, it returns null exception. — Ahmed Mohamed, Sep 15 '21 at 00:20

score 0 · Answer 1 · answered Sep 15 '21 at 01:49

This is not really the answer for my question, but a temporary solution if someone has the same issue.

So the thing is, If the image is null, I will just tell the ImageFileValidator to send True to ValidImage and then the image will be validated. Which means I don't have to send errors.

@Override
    public boolean isValid(MultipartFile multipartFile, ConstraintValidatorContext context) {

        boolean result = true;
        String contentType = "";
        try {
            contentType = multipartFile.getContentType();
            if(fileNameLength(multipartFile) == 0) {
                return result;
            }
        } catch(NullPointerException e) {
            e.printStackTrace();
            
        }

if (!isSupportedContentType(contentType)) {
.....

The rest of the code can be found above. It might return NullException as well, so make sure to handle it.

Validate image if existing or not null only in spring boot?

1 Answers1