How do I display validation errors about an uploaded multipart file using Spring MVC

Question

I have a Spring MVC application with a file upload form.

I would like to be able to display validation errors to a user if the upl

Answer 1

If you are using Java Bean Validation (JSR 303) you can make annotation that validates content type. See code below.

import static java.lang.annotation.ElementType.*;
import static java.lang.annotation.RetentionPolicy.*;
/**
 * The annotated element must have specified content type.
 *
 * Supported types are:
 * 

 * 
MultipartFile
 * 
 *
 * @author Michal Kreuzman
 */
@Documented
@Retention(RUNTIME)
@Constraint(validatedBy = {ContentTypeMultipartFileValidator.class})
@Target({ METHOD, FIELD, ANNOTATION_TYPE, CONSTRUCTOR, PARAMETER })
public @interface ContentType {

    String message() default "{com.kreuzman.ContentType.message}";

    Class[] groups() default {};

    Class[] payload() default {};

/**
 * Specify accepted content types.
 *
 * Content type example :
 * 

 * 
application/pdf - accepts PDF documents only
 * 
application/msword - accepts MS Word documents only
 * 
images/png - accepts PNG images only
 * 
 *
 * @return accepted content types
 */
     String[] value();
}

---

/**
  * Validator of content type. This is simple and not complete implementation
  * of content type validating. It's based just on String equalsIgnoreCase
  * method.
  *
  * @author Michal Kreuzman
  */
 public class ContentTypeMultipartFileValidator implements ConstraintValidator {

private String[] acceptedContentTypes;

@Override
public void initialize(ContentType constraintAnnotation) {
    this.acceptedContentTypes = constraintAnnotation.value();
}

@Override
public boolean isValid(MultipartFile value, ConstraintValidatorContext context) {
    if (value == null || value.isEmpty())
        return true;

    return ContentTypeMultipartFileValidator.acceptContentType(value.getContentType(), acceptedContentTypes);
}

private static boolean acceptContentType(String contentType, String[] acceptedContentTypes) {
    for (String accept : acceptedContentTypes) {
            // TODO this should be done more clever to accept all possible content types
        if (contentType.equalsIgnoreCase(accept)) {
            return true;
        }
    }

    return false;
}
}

---

public class MyModelAttribute {

@ContentType("application/pdf")
private MultipartFile file;

public MultipartFile getFile() {
    return file;
}

public void setFile(MultipartFile file) {
    this.file = file;
}
}
@RequestMapping(method = RequestMethod.POST)
public String processUploadWithModelAttribute(@ModelAttribute("myModelAttribute") @Validated final MyModelAttribute myModelAttribute, final BindingResult result, final Model model) throws IOException {
 if (result.hasErrors()) {
     // Error handling
     return "fileupload";
 }

 return "fileupload";
}