iterating a HashSet ...

Sometimes i miss some people around me at work or home that can feed me with some java facts.

The last week i work on a from component that contains an AjaxFormLoop to edit a set of drivers (removing/adding) to an parent entity.

Thanks Tapestry it was a fine quick job to design the UI but than began the fight to save
the modified HashSet, many pitfalls i tapped but now the job is done.

my first solution was:

    void onAfterSubmit()
    {
        for (FreightDriver driver : entity.getDrivers())
        {
            boolean mustRemoved = true;
            for (FreightDriver freightDriver : DB.values())
            {
                if (driver.getId() == freightDriver.getId())
                {
                    mustRemoved = false;
                    break;
                }
            }

            if (mustRemoved)
                entity.getDrivers().remove(driver);
        }
    }

but this throws a ConcurrentModificationException
after a while i found the right (IMHO) solution:

    void onAfterSubmit()
    {
        List driversToDelete = new ArrayList();

        //-------------------------------------------------
        // ----->  Start to delete drivers from HashSet
        //-------------------------------------------------
        for (FreightDriver driver : entity.getDrivers())
        {
            boolean mustRemoved = true;
            for (FreightDriver freightDriver : DB.values())
            {
                if (driver.getId() == freightDriver.getId())
                {
                    mustRemoved = false;
                    break;
                }
            }

            if (mustRemoved)
                driversToDelete.add(driver);
        }

        for (FreightDriver freightDriver : driversToDelete)
            entity.getDrivers().remove(freightDriver);
        //-------------------------------------------------
        // ----->  End delete drivers from HashSet
        //-------------------------------------------------
   }

and here the complete component

@IncludeStylesheet(value = {"DriverGrid.css"})
public class DriverGrid
{
    private static final Map DB = CollectionFactory.newConcurrentMap();

    private static final AtomicLong ID_ALLOCATOR = new AtomicLong(System.currentTimeMillis());

    @Parameter(required = true, defaultPrefix = BindingConstants.PROP)
    private FreightOrder entity;

    @Inject
    private Session session;

    @Inject
    private Logger logger;

    @Inject
    private Messages messages;

    /**
     * Request object for information on current request.
     */
    @Inject
    private Request request;

    /**
     * RenderSupport to get unique client side id.
     */
    @Inject
    private RenderSupport renderSupport;

    /**
     * For blocks, messages, crete actionlink, trigger event.
     */
    @Inject
    private ComponentResources resources;

    @Inject
    @Property
    private Block addRowBlock;

    @Property
    private FreightDriver gridRow;

    @Inject
    private EmptyBeanModelSource beanModelSource;

    @Inject
    private StaffDAO staffDAO;

    @Inject
    private FreightDriverDAO freightDriverDAO;

    @Retain
    @Property
    private BeanModel gridModel;

    /**
     * ----------------------------------------------------------
     * Drivers Grid
     * ----------------------------------------------------------
     */
    @Component(parameters = {"source=gridSource", "value=gridRow", "encoder=encoder",
            "addrow=block:addRowBlock"})
    private AjaxFormLoop grid;

    @Component
    private AddRowLink addRowLink;

    @Component
    private RemoveRowLink removeRowLink;

    @Component(parameters = {"value=gridRow.driver"})
    private StaffAutoTextField inputDriver;

    @Component(parameters = {"value=gridRow.freightPrice", 
                             "validate=required,min=0"})
    private TextField inputFreightPrice;

    @Component(parameters = {"value=gridRow.diversePrice", 
                             "validate=required,min=0"})
    private TextField inputDiversePrice;

    /**
     * get the datasource for the driver grid.
     */
    @Log
    public Collection getGridSource()
    {
        return DB.values();
    }

    /**
     * Tapestry render phase method.
     * Initialize temporary instance variables here.
     */
    @Log
    public void setupRender()
    {
        DB.clear();
        for (FreightDriver driver : entity.getDrivers())
        {
            driver.setMapId(ID_ALLOCATOR.getAndIncrement());
            DB.put(driver.getMapId(), driver);
        }
    }

    @Log
    void onBeginSubmit()
    {
    }

    @Log
    void onAfterSubmit()
    {
        List driversToDelete = new ArrayList();

        //-------------------------------------------------
        // ----->  Start to delete drivers from HashSet
        //-------------------------------------------------
        for (FreightDriver driver : entity.getDrivers())
        {
            boolean mustRemoved = true;
            for (FreightDriver freightDriver : DB.values())
            {
                if (driver.getId() == freightDriver.getId())
                {
                    mustRemoved = false;
                    break;
                }
            }

            if (mustRemoved)
                driversToDelete.add(driver);
        }

        for (FreightDriver freightDriver : driversToDelete)
            entity.getDrivers().remove(freightDriver);
        //-------------------------------------------------
        // ----->  End delete drivers from HashSet
        //-------------------------------------------------

        for (FreightDriver freightDriver : DB.values())
        {
            if (freightDriver.getId() == 0)
            {
                freightDriver.setOrder(entity);
                entity.getDrivers().add(freightDriver);
            }
        }
    }

    /**
     * add a new row.
     */
    @Log
    Object onAddRow()
    {
        FreightDriver driver = new FreightDriver();
        driver.setMapId(ID_ALLOCATOR.getAndIncrement());
        DB.put(driver.getMapId(), driver);
        return driver;
    }

    /**
     * remove a new row.
     */
    @Log
    void onRemoveRow(FreightDriver value)
    {
        DB.remove(value.getMapId());
    }

    /**
     * tells the ajax loop how to encode the items.
     */
    @Log
    public PrimaryKeyEncoder getEncoder()
    {
        return new PrimaryKeyEncoder()
        {
            public Long toKey(FreightDriver value)
            {
                return value.getMapId();
            }

            public void prepareForKeys(List keys)
            {
            }

            public FreightDriver toValue(Long key)
            {
                return DB.get(key);
            }
        };
    }

    /**
     * create response for driver autocompleter.
     */
    @OnEvent(value = "selectDriver")
    StreamResponse selectDriver()
    {
        String driverName = request.getParameter("inputDriver");
        List staffs = staffDAO.findByPartialName(driverName, false);
        StringBuffer stringBuffer = new StringBuffer();

        stringBuffer.append("<ul>");
        for (Staff staff : staffs)
        {
            stringBuffer.append("<li id='").
                         append(staff.getRecId()).
                         append("'>");
            stringBuffer.append(staff.getAddress().getName1()).
                         append(", ").
                         append(staff.getAddress().getName2()).
                         append(" (").
                         append(staff.getClient().getClientDesc()).
                         append(")");
            stringBuffer.append("</li>");
        }
        stringBuffer.append("</ul>");

        return new TextStreamResponse("text/html", stringBuffer.toString());
    }
}