Spring MVC: Saving Enum from JSP to Bean

I work in an industry where we work closely with publishing houses and publications. We use the Spring MVC framework with the usual controllers, services and views (currently JSP). I was tasked to write an internal marketing application that will send automatic emails to various publications (“Mediums”) whenever they or one of their books/magazines is mentioned on our website.  The application will have to save the medium name and standard emails texts in several languages.
 

The Files

 
Controller
When a new record has to be made, the controller executes the following code and returns the view. The language is passed as a model attribute.

@GetMapping(path="/new")
public String newMedium(HttpServletRequest request, Model model, @ModelAttribute(name = "bookMarketingForm") BookMarketingMediumForm bookMarketingForm) throwsBaseException
{
model.addAttribute("allLanguages", getAllLanguages());
       return "pps/bookmarketing/bookmarketing-save";
}
 
@ModelAttribute("allLanguages")
protected Language[] getAllLanguages()
{
       return Language.values();
}

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Language Enum
Language is an Enum class that contains all the languages used by our company.

public enum Language
{
   EN(new Locale("en", "US"), true),
   DE(new Locale("de", "DE"), true),
   ES(new Locale("es", "ES"), true),
   RU(new Locale("ru", "RU"), false),
   ZH(new Locale("zh", "CN"), false),
   PT(new Locale("pt", "BR"), true),
   FR(new Locale("fr", "FR"), true);


   /**
    * Find the best suitable supported Language for the given ISO code.
    * Defaults to Language.EN if the isoCode is null, not supported or malformed.
    * @param isoCode either a two letter ISO language code or an IETF BCP 47 language tag string as described in {@link Locale#forLanguageTag(String)}. <code>null</code> defaults to Language.EN.
    * @return always a Language
    */
   public static Language ofIsoCode(String isoCode)
   {
      if (isoCode == null)
      {
         return Language.EN;
      }
      if (isoCode.length() == 2)
      {
         return Optional.ofNullable(EnumUtils.getEnum(Language.class, isoCode.toUpperCase())).orElse(Language.EN);
      }
      else if (isoCode.length() > 2)
      {
         final Locale requestedLocale = Locale.forLanguageTag(isoCode.replaceAll("_", "-"));
         return ofLocale(requestedLocale);
      }
      else
      {
         return Language.EN;
      }
   }
   /**
    * Find the best suitable supported Language for the given Locale.
    * Defaults to Language.EN.
    * @param locale <code>null</code> defaults to Language.EN
    * @return always a Language
    */
   public static Language ofLocale(Locale locale)
   {
      if (locale == null) {
         return Language.EN;
      } else {
         return Arrays.stream(Language.values())
               .filter(l -> l.locale.getLanguage().equals(locale.getLanguage()))
               .findFirst()
               .orElse(Language.EN);
      }
   }


   private final Locale locale;


   public final boolean latinScript;


   private Language(Locale locale, boolean latinScript)
   {
      this.locale = locale;
      this.latinScript = latinScript;
   }


   /**
    * Return the two-letter ISO language code.
    * @return a two character ASCII String like &quot;en&quot;;
    */
   @JsonValue
   public String getIsoCode()
   {
      return locale.getLanguage();
   }


   /**
    * Return the corresponding Java Locale including the country
    * code of the language variant we support.
    * @return a Java locale like <code>en_EN</code>.
    */
   public Locale getLocale()
   {
      return locale;
   }


   /**
    * Whether or not the language uses latin alphabet. Useful to decide on fonts.
    * @return true if the language uses primarily latin alphabet characters, false otherwise.
    */
   public boolean isLatinScript()
   {
      return latinScript;
   }


   /**
    * The two-letter lower-case ISO language code for the language.
    */
   @Override
   public String toString()
   {
      return getIsoCode();
   }

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AttributeConverter
As I am dealing with Enums, I created an attribute converter that converts from String to Language and vice versa.
 

@Converter(autoApply = true)
publicclass BookMarketingMediumEmailLanguageConverter implements AttributeConverter<Language, String> {
 
       @Override
       public String convertToDatabaseColumn(Language attribute) {
              return attribute.getIsoCode();
       }
 
       @Override
       public Language convertToEntityAttribute(String isoCode) {
              return Language.ofIsoCode(isoCode);
       }
 }

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The Bean
The bean (or form as we call it) contains the following fields. There are no getters/setters as it is handled by Lombok (@Data).

@Data
publicclass BookMarketingMediumForm
{
       private int bookMarketingMediumId;
 
       private @Resource Map<Language, BookMarketingMediumEmailView> bookMarketingMediumEmails = new TreeMap<>();
 
       @NotBlank
       private String bookMarketingMediumDE;
 
       @NotBlank
       private String bookMarketingMediumEN;
}

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The View

The view receives all the languages, loops through all languages

<c:forEach var="language" items="${allLanguages}">
<c:set var="bookMarketingLanguage" value="${language}" />
                                                 
 <form:input type="textarea" path="bookMarketingMediumEmails[${language}].email"  label="Email text" rows="8" cssStyle="margin-bottom: 15px"/>
 
 <form:input type="text" path="bookMarketingMediumEmails[${language}].subject" label="Email Subject" maxlength="40"/>
                                     
                                   
</c:forEach>

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The Problem

The problem is, that the languages cannot be displayed as there is a problem with the JSP.
 

2020-10-25 18:48:47,833 
JAVA org.springframework.web.util.NestedServletException: Request processing failed; nested exception is org.springframework.beans.InvalidPropertyException: Invalid property 'bookMarketingMediumEmails[en]' of bean class 

[com.getabstract.web.pps.bookmarketing.BookMarketingMediumForm]: Invalid index in property path 'bookMarketingMediumEmails[en]'; nested exception is 
org.springframework.beans.TypeMismatchException: Failed to convert property value of type 'java.lang.String' to required type 'com.getabstract.common.util.i18n.Language' for property 'null'; 

nested exception is org.springframework.core.convert.ConversionFailedException: Failed to convert from type [java.lang.String] to type [com.getabstract.common.util.i18n.Language] for value 'en'; 

nested exception is java.lang.IllegalArgumentException: No enum constant com.getabstract.common.util.i18n.Language.en

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I have attached a screenshot of what the application should look like.

Is the problem that I cannot pass an Enum in Map from the view (JSP) to the Bean?

Any suggestions on how to solve this?

Thanks for your help

Massimo