How get string value in enum?

Question

I have a enum with an String attribute like this:

public enum CategoriaRischio {
    a1a1("classificati in cat. III e IV,o contenenti gas instabili appartenenti alla cat. dalla I alla IV"), 
    a1a2("classificati in cat. I e II"), 
    a1a5("liquidi appartenenti a cat. I,II e III"), 
    a1b1("Gas compressi, liquefatti, disciolti o vapori diversi dal vapor d'acqua in cat.III e IV, recipienti di vapore d'acqua e d'acqua surriscaldata in cat. da I a IV"), 
    a1b2("Gas compressi, liquefatti, disciolti o vapori diversi dal vapor d'acqua in cat.I e II");

    private String descrizioneCategoria;

    public String getDescrizioneCategoria() {
        return descrizioneCategoria;
    }

    private CategoriaRischio(final String descrizioneCategoria){
        this.descrizioneCategoria = descrizioneCategoria;
    }

}

I want to show the string value in JSP page. How can I do this?

You cannot refer Constants through EL. So, you won't be able to access Enum through EL code. javaranch.com/journal/200601/Journal200601.jsp#a3 will help you for building custom tags and access Constants through EL. — Sudarshan_SMD
– Sudarshan_SMD, Commented Jan 22, 2014 at 9:37

Teo · Accepted Answer · 2014-01-22 09:33:03Z

1

You can use a formatter like this:

public class MyFormatter implements Formatter<CategoriaRischio>
{

  @Override
  public String print(CategoriaRischio cat, Locale locale) 
  {
  return cat.getCategoriaRischio();
  }

  @Override
  public CategoriaRischio parse(String text, Locale locale) throws ParseException 
  {
    return CategoriaRischio.valueOf(text);
  }
}

And then you must register the formatter in you servlet context, in this way:

<mvc:annotation-driven conversion-service="conversionService">
      </mvc:annotation-driven>

      <!-- Custom formatters -->
      <bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="formatters">
          <set>
            <bean class= "yourPackage.MyFormatter" />
          </set>
        </property>
      </bean>

edited Jan 22, 2014 at 9:33

answered Jan 22, 2014 at 9:21

Teo

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1 Comment

Ralph Over a year ago

Your parse implementation looks like it is copied from an other problem, and does not match the question -- anyway the print implementation looks ok

Ralph · Accepted Answer · 2014-01-22 09:57:07Z

I have implemented a Printer for printing (So you can convert the Enum to String, but not the other way around.

In the code below, you will find an example where the String/Name/Value/How-ever-you-call-it, is taken from a MessageSource (message property file) - this allows to support multiple languages.

public class EnumToStringPrinter implements Printer<Enum<?>> {

    /** Use the same immutable value instead of creating an new array every time. */
    private static final Object[] NO_PARAM = new Object[0];

    /** The prefix of all message codes. */
    private static final String PREFIX = "label_";

    /** The separator in the message code, between different packages as well as between package can class. */
    private static final String PACKAGE_SEPARATOR = "_";

    /** The separator in the message code, between the class name and the enum case name. */
    private static final String ENUM_CASE_SEPARATOR = "_";

    /** The message source. */
    private MessageSource messageSource;

    @Autowired
    public EnumToStringPrinter(final MessageSource messageSource) {
        if(messageSource == null) {
            throw new RuntimeException("messageSource must not be null");
        }

        this.messageSource = messageSource;
    }

    @Override
    public String print(final Enum<?> source, final Locale locale) {
        /* locale null can mean default locale, this depends on the messageSource implmentation */
        if (source != null) {
            String enumValueName = source.name();
            String code = PREFIX + source.getClass().getName().toLowerCase().replace(".", PACKAGE_SEPARATOR)
                    + ENUM_CASE_SEPARATOR + enumValueName.toLowerCase();

            String message = messageSource.getMessage(code, NO_PARAM, enumValueName, locale);

            return message;
        } else {
            return "";
        }
    }    
}

The mayor drawback with Printers is, that it is hard to register them in Spring. Therefor I implemented a Printer2ConverterAdapter. and used the adaptor to register the Printer like a X->String Converter

/**
 * Adapter that adapts a {@link Printer} to an Converter, more correct to an {@link GenericConverter}.
 *
 * Follows the Object Adapter pattern:
 * <ul>
 *   <li>Adaptor - this class</li>
 *   <li>Target - {@link GenericConverter}</li>
 *   <li>Adaptee - the Printer {@link #Printer2ConverterAdapter(Printer)}</li>
 * </ul>
 *
 * @author Ralph
 */
public class Printer2ConverterAdapter implements GenericConverter {

    private final Class<?> printerObjectType;

    @SuppressWarnings("rawtypes")
    private final Printer printer;

    public <T> Printer2ConverterAdapter(final Printer<T> printer) {
        this.printerObjectType = resolvePrinterObjectType(printer);
        this.printer = printer;
    }

    @Override
    public Set<ConvertiblePair> getConvertibleTypes() {
        return Collections.singleton(new ConvertiblePair(this.printerObjectType, String.class));
    }

    @SuppressWarnings("unchecked")
    @Override
    public Object convert(final Object source, final TypeDescriptor sourceType, final TypeDescriptor targetType) {
        if (source == null) {
            return "";
        }
        return this.printer.print(source, LocaleContextHolder.getLocale());
    }

    private Class<?> resolvePrinterObjectType(final Printer<?> printer) {
        return GenericTypeResolver.resolveTypeArgument(printer.getClass(), Printer.class);
    }

    @Override
    public String toString() {
        return this.printerObjectType.getName() + " -> java.lang.String : " + this.printer;
    }

}

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