Custom annotation in JPA

Entry in orm.xml

<persistence-unit-metadata>
<persistence-unit-defaults>
<entity-listeners>
<entity-listener class="com.wdpr.dataaccess.jpa.EntityAuditListener" />
<entity-listener class="com.wdpr.dataaccess.jpa.SpaceRTrimListener" />
</entity-listeners>
</persistence-unit-defaults>
</persistence-unit-metadata>

Listener class

package com.wdpr.dataaccess.jpa;

import com.wdpr.dataaccess.annotation.RTrim;
import java.lang.reflect.Field;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import javax.persistence.PrePersist;
import javax.persistence.PreUpdate;

public class SpaceRTrimListener
{
  private static final Map<Class<?>, Set<Field>> trimProperties = new HashMap();
  private static final String EMPTY_STRING = "";
  private static final String RIGHT_TRIM_PATTERN = "\\s+$";

  @PrePersist
  @PreUpdate
  public void rTrimnSpaces(Object entity)
    throws Exception
  {
    for (Field fieldToTrim : getTrimProperties(entity.getClass()))
    {
      String propertyValue = (String)fieldToTrim.get(entity);
      if (propertyValue != null)
      {
        fieldToTrim.set(entity, rightTrim(propertyValue));
      }
    }
  }

  private String rightTrim(String propertyValue)
  {
    if ((propertyValue != null) && (!"".equals(propertyValue.trim())))
    {
      propertyValue = propertyValue.replaceAll("\\s+$", "");
    }
    return propertyValue;
  }

  private Set<Field> getTrimProperties(Class<?> entityClass) throws Exception
  {
    if (Object.class.equals(entityClass))
    {
      return Collections.emptySet();
    }
    Set propertiesToTrim = (Set)trimProperties.get(entityClass);
    if (null == propertiesToTrim)
    {
      propertiesToTrim = new HashSet();
      for (Field field : entityClass.getDeclaredFields())
      {
        if (field.getAnnotation(RTrim.class) == null)
          continue;
        if (field.getType().equals(String.class))
        {
          field.setAccessible(true);
          propertiesToTrim.add(field);
        }
        else {
          String errorMessage = "Entity : " + entityClass.getName() + " Field : " + field.getName() + " of type : " + field.getType() + " cannot use Rtrim annotation";

          throw new IllegalArgumentException(errorMessage);
        }
      }

      trimProperties.put(entityClass, propertiesToTrim);
    }
    return propertiesToTrim;
  }

}