Generic JSF entity converter [duplicate]

This question already has answers here: Implement converters for entities with Java Generics (3 answers) Closed 7 years ago.

I'm writing my first Java EE 6 web app as a learning exercise. I'm not using a framework, just JPA 2.0, EJB 3.1 and JSF 2.0.

I have a Custom Converter to convert a JPA Entity stored in a SelectOne component back to an Entity. I'm using an InitialContext.looku开发者_Python百科p to obtain a reference to a Session Bean to find the relevant Entity.

I'd like to create a generic Entity Converter so I don't have to create a converter per Entity. I thought I'd create an Abstract Entity and have all Entities extend it. Then create a Custom Converter for the Abstract Entity and use it as the converter for all Entities.

Does that sound sensible and/or practicable?

Would it make more sense not to have an abstract entity, just a converter that converts any entity? In that case I'm not sure how I'd obtain a reference to the appropriate Session Bean.

I've included my current converter because I'm not sure I'm obtaining a reference to my Session Bean in the most efficient manner.

package com.mycom.rentalstore.converters;

import com.mycom.rentalstore.ejbs.ClassificationEJB;
import com.mycom.rentalstore.entities.Classification;
import javax.faces.application.FacesMessage;
import javax.faces.component.UIComponent;
import javax.faces.context.FacesContext;
import javax.faces.convert.Converter;
import javax.faces.convert.ConverterException;
import javax.faces.convert.FacesConverter;
import javax.naming.InitialContext;
import javax.naming.NamingException;

@FacesConverter(forClass = Classification.class)
public class ClassificationConverter implements Converter {

    private InitialContext ic;
    private ClassificationEJB classificationEJB;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {

        try {
            ic = new InitialContext();
            classificationEJB = (ClassificationEJB) ic.lookup("java:global/com.mycom.rentalstore_RentalStore_war_1.0-SNAPSHOT/ClassificationEJB");

        } catch (NamingException e) {
            throw new ConverterException(new FacesMessage(String.format("Cannot obtain InitialContext - %s", e)), e);
        }

        try {
            return classificationEJB.getClassificationById(Long.valueOf(value));
        } catch (Exception e) {
            throw new ConverterException(new FacesMessage(String.format("Cannot convert %s to Classification - %s", value, e)), e);
        }
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        return String.valueOf(((Classification) value).getId());
    }
}

---

I am using JSF 2.0 view map:

@FacesConverter("entityConverter")
public class EntityConverter implements Converter {

private static final String key = "com.example.jsf.EntityConverter";
private static final String empty = "";

private Map<String, Object> getViewMap(FacesContext context) {
    Map<String, Object> viewMap = context.getViewRoot().getViewMap();
    @SuppressWarnings({ "unchecked", "rawtypes" })
    Map<String, Object> idMap = (Map) viewMap.get(key);
    if (idMap == null) {
        idMap = new HashMap<String, Object>();
        viewMap.put(key, idMap);
    }
    return idMap;
}

@Override
public Object getAsObject(FacesContext context, UIComponent c, String value) {
    if (value.isEmpty()) {
        return null;
    }
    return getViewMap(context).get(value);
}

@Override
public String getAsString(FacesContext context, UIComponent c, Object value) {
    if (value == null) {
        return empty;
    }
    String id = ((Persistent) value).getId().toString();
    getViewMap(context).put(id, value);
    return id;
}
}

---

Well I had the same problem today, and I solved it by creating a generic ConversionHelper and using it in the converter. For this purpose I have an EntityService which is a generic SLSB that I use to perform simple CRUD operations for any entity type. Also my entities implement a PersistentEntity interface, which has a getId and setId methods and I keep them with simple primary keys. That's it.

In the end my converter looks like this:

@FacesConverter(value = "userConverter", forClass = User.class)
public class UserConverter implements Converter {

    @Override
    public Object getAsObject(FacesContext ctx, UIComponent component, java.lang.String value) {

        return ConversionHelper.getAsObject(User.class, value);
    }

    @Override
    public String getAsString(FacesContext ctx, UIComponent component, Object value) {

        return ConversionHelper.getAsString(value);
    }
}

And my conversion helper looks like this:

public final class ConversionHelper {

    private ConversionHelper() {
    }

    public static <T> T getAsObject(Class<T> returnType, String value) {

        if (returnType== null) {

            throw new NullPointerException("Trying to getAsObject with a null return type.");
        }

        if (value == null) {

            throw new NullPointerException("Trying to getAsObject with a null value.");
        }

        Long id = null;

        try {

            id = Long.parseLong(value);

        } catch (NumberFormatException e) {

            throw new ConverterException("Trying to getAsObject with a wrong id format.");
        }

        try {

            Context initialContext = new InitialContext();
            EntityService entityService = (EntityService) initialContext.lookup("java:global/myapp/EntityService");

            T result = (T) entityService.find(returnType, id);

            return result;

        } catch (NamingException e) {

            throw new ConverterException("EntityService not found.");
        }
    }

    public static String getAsString(Object value) {

        if (value instanceof PersistentEntity) {

            PersistentEntity result = (PersistentEntity) value;

            return String.valueOf(result.getId());
        }

        return null;
    }
}

Now creating converters for simple JPA entities is a matter of duplicate a converter and change 3 parameters.

This is working well for me, but I don't know if it is the best approach in terms of style and performance. Any tips would be appreciated.

---

my solution is the following :

@ManagedBean
@SessionScoped
public class EntityConverterBuilderBean {
    private static Logger logger = LoggerFactory.getLogger(EntityConverterBuilderBean.class);
    @EJB
    private GenericDao dao;

    public GenericConverter createConverter(String entityClass) {
        return new GenericConverter(entityClass, dao);
    }


}

public class GenericConverter implements Converter {

    private Class clazz;
    private GenericDao dao;

    public GenericConverter(String clazz, Generic dao) {
        try {
            this.clazz = Class.forName(clazz);
            this.dao = dao;
        } catch (Exception e) {
            logger.error("cannot get class: " + clazz, e);
            throw new RuntimeException(e);
        }
    }

    public Object getAsObject(javax.faces.context.FacesContext facesContext, javax.faces.component.UIComponent uiComponent, java.lang.String s) {
        Object ret = null;

        if (!"".equals(s)) {
            Long id = new Long(s);
            ret = dao.findById(clazz, id);
        }

        return ret;
    }

    public String getAsString(javax.faces.context.FacesContext facesContext, javax.faces.component.UIComponent uiComponent, java.lang.Object o) {
        if (o != null) {
            return ((SimpleEntity) o).getId() + "";
        } else {
            return "";
        }
    }
}

and in pages:

 <h:selectOneMenu id="x" value="#{controller.x}" 
      converter="#{entityConverterBuilderBean.createConverter('com.test.model.TestEntity')}">

---

Use Seam Faces, it provides a Converter class that does what you want.

org.jboss.seam.faces.conversion.Converter

While it's a JBoss project, Seam 3 works fine with Glassfish 3.1 and newer.

http://seamframework.org/Seam3/FacesModule

On 3.1 it does have a couple of additional dependencies; see http://blog.ringerc.id.au/2011/05/using-seam-3-with-glassfish-31.html

---

Try this using Seam Faces from Seam 3.

@Named("DocTypeConverter")
public class DocumentTypeConverter implements Converter, Serializable {

    private static final long serialVersionUID = 1L;

    @Inject
    private DocumentTypeSessionEJB proDocTypeSb;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component,
            String value) {
        DocumentType result = null;

        if (value != null && !value.trim().equals("")) {  
            try {  
                result = (DocumentType) proDocTypeSb.findById(DocumentType.class, value);
            } catch(Exception exception) {  
                throw new ConverterException(new FacesMessage(FacesMessage.SEVERITY_ERROR, "Conversion Error", "Not a valid value"));  
            }  
        }  

        return result;
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component,
            Object value) {
        String result = null;
        if (value != null && value instanceof DocumentType){
            DocumentType docType = (DocumentType) value;
            result = docType.getId();
        }

        return result;
    }

}

---

(UPDATED FOR JSF 2.3)

I am using something like this:

@FacesConverter(value = "entityConverter", managed = true)
public class EntityConverter implements Converter<Object> {

    @Inject
    private EntityManager entityManager;

    @Override
    public Object getAsObject(FacesContext context, UIComponent component, String value) {
        Class<?> entityType = component.getValueExpression("value").getType(context.getELContext());
        Class<?> idType = entityManager.getMetamodel().entity(entityType).getIdType().getJavaType();
        Converter idConverter = context.getApplication().createConverter(idType);
        Object id = idConverter.getAsObject(context, component, value);
        return entityManager.getReference(entityType, id);
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component, Object value) {
        Object id = entityManager.getEntityManagerFactory().getPersistenceUnitUtil().getIdentifier(value);
        Converter idConverter = context.getApplication().createConverter(id.getClass());
        return idConverter.getAsString(context, component, id);
    }
}

In template, use <f:converter binding="#{entityConverter}" />.

---

To complete the response of Craig Ringer, you can use the generic org.jboss.seam.faces.conversion.ObjectConverter of the Seam 3 FacesModule.

You can grab the code here : https://github.com/seam/faces/blob/develop/impl/src/main/java/org/jboss/seam/faces/conversion/ObjectConverter.java

It uses 2 HashMaps (one is used reversly) and stocks its objects in the Conversation.