Custom GWT Column extension that offers JSR-303 client-side support for validating cell value within a column (incl. error message pop-up panel)

AbstractValidatatableColumn

import java.util.Set;

import javax.validation.ConstraintViolation;
import javax.validation.Validation;
import javax.validation.Validator;

import com.google.gwt.user.cellview.client.AbstractHasData;
import com.google.gwt.user.cellview.client.Column;

/**
 * A {@link Column} implementation that encapsulates a {@link ValidatableInputCell}.
 * Performs JSR-303 validation on a field (or nested field) of the type.
 * @author cphillipson
 *
 * @param <T> the type
 * @param <O> the owning type of the field to be validated; in many cases T may have only primitive or wrapper types, therefore O could be the same type as T
 */
public abstract class AbstractValidatableColumn<T, O> extends Column<T, String> {

    /**
     * Preferred constructor.
     * Allows for definition of tabIndex but uses a default for the input cell size.
     * @param tabIndex the <code>tabindex</code> attribute's value for the input cell
     * @param table the grid instance
     */
    public AbstractValidatableColumn(int tabIndex, final AbstractHasData<T> table) {
        this(App.INSTANCE.defaultValidatableInputCellSize(), tabIndex, table);
    }

    /**
     * Overloaded constructor.
     * Allows for definition of tabIndex and allows for an override to the default for the input cell size.
     * @param inputSize the <code>size</code> attribute's value for the input cell
     * @param tabIndex the <code>tabindex</code> attribute's value for the input cell
     * @param table the grid instance
     */
    public AbstractValidatableColumn(int inputSize, int tabIndex, final AbstractHasData<T> table) {
        super(new ValidatableInputCell());
        getCell().setInputSize(inputSize);
        getCell().setTabIndex(tabIndex);
        init(table);
    }

    // meat and potatoes
    private void init(final AbstractHasData<T> table) {
        setFieldUpdater(new ValidatableFieldUpdater(table, this));
    }


    /**
     * Attempts conversion of a String value into another type
     * Instances are responsible for the conversion logic as it may vary from type to type
     * @param value a String value to be converted into an owning class's property type
     * @return a ConversionResult
     */
    protected abstract ConversionResult attemptValueConversion(String value);

    @Override
    public ValidatableInputCell getCell() {
        return (ValidatableInputCell) super.getCell();
    }

    /**
     * Template method for updating a field (or nested field) value within a DTO
     * @param index the row index for the instance of the DTO within the grid
     * @param dto the object whose field we wish to update
     * @param value the new value that will be set on a field (or nested field) of the DTO
     */
    protected abstract void doUpdate(int index, T dto, String value);

    /**
     * Template method for specifying the property name of an owning class
     * @return the field name of the owning class whose value is to be updated
     */
    protected abstract String getPropertyName();

    /**
     * Template method for specifying the owning class
     * @return the owning class of the field whose value is to be updated
     */
    protected abstract Class<O> getPropertyOwner();

    /**
     * Validates a value against a set of constraints (i.e., JSR-303 annotations on a field)
     * @param newValue the value to be validated
     * @return the set of constraint violations induced by an inappropriate value
     */
    protected Set<ConstraintViolation<O>> validate(Object newValue) {
        final Validator validator = Validation.buildDefaultValidatorFactory().getValidator();
        final Set<ConstraintViolation<O>> violations = validator.validateValue(getPropertyOwner(), getPropertyName(), newValue);
        return violations;
    }

}