JPA @TableGenerator does not allow for data type c

问题:

I'm trying to generate an auto ID. My problem is that my ID-generating class uses a String (varchar in db) but the entity being created uses an Integer (numeric in db).

I tried using a converter on the ID-generating class. Although sParamValue is a varchar in our db, I thought I could convert it to Integer, ie:

IDGenerator.class :

@Entity
@Table(name = "idGenerator")
@XmlRootElement
@NamedQueries(
{
   //some queries here
})
@Data
public class IDGenerator implements Serializable
{
    @Basic(optional = false)
        @NotNull
        @Size(min = 1, max = 128)
        @Column(name = "sParamValue")
        @Convert(converter = OptionalIntegerConverter.class)
        private Integer sParamValue;
...
}

Class in need of ID:

 public class MyClass implements Serializable
    {
        @Id
            @Basic(optional = false)
            @NotNull
            @GeneratedValue(generator = "TABLE_SEQ", strategy = GenerationType.TABLE)
            @TableGenerator(name = "TABLE_SEQ",
                    table = "idGenerator",
                    pkColumnName = "sParamName", 
                    valueColumnName = "sParamValue", 
                    pkColumnValue = "NextIdNumber", 
                    allocationSize = 1)
            @Column(name = "idNum")
private Integer idNum;
    }

Unfortunately, MyClass does not get the converted value of sParamValue but just gets the String directly from the database, and then I get an error:

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Number
        at org.eclipse.persistence.sequencing.QuerySequence.updateAndSelectSequence(QuerySequence.java:278)
        at org.eclipse.persistence.sequencing.StandardSequence.getGeneratedVector(StandardSequence.java:71)
        at org.eclipse.persistence.sequencing.Sequence.getGeneratedVector(Sequence.java:257)
        at org.eclipse.persistence.internal.sequencing.SequencingManager$Preallocation_Transaction_NoAccessor_State.getNextValue(SequencingManager.java:549)

Any ideas on how to make a converter work?

I could change the data type of MyClass.idNum to String, use the converter there, and make changes throughout my code, but that's an ugly solution.

I wonder if I could do what is described here and create a custom generator which would query my idGenerator table. It's important that no other access to idGenerator be allowed while I'm getting the latest id. I'm assuming @TableGenerator is transactional, but is the EclipseLink generator?