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Asked: 2026-05-26T11:13:08+00:00

I have an existing DataTable built in Wicket 1.5 as follows: The Page’s java

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I have an existing DataTable built in Wicket 1.5 as follows:

The Page’s java file.

public class ExamplePage extends WebPage {
public ExamplePage(){
List<IColumn<Example>> columns = new ArrayList<IColumn<Example>>();
columns.add(new PropertyColumn<Example>(Model.of("name"), "name"));
ExampleProvider provider = new ExampleProvider();

        DataTable<Example> exampleTable = new DataTable<Example>("exampleTable", columns, provider, 10);
        exampleTable.addTopToolbar(new HeadersToolbar(exampleTable, null));
        exampleTable.addBottomToolbar(new NavigationToolbar(exampleTable));
        add(exampleTable);
    }
}

The Provider

public class ExampleProvider extends SortableDataProvider<Example> {
    @SpringBean
    ExampleDao exampleDao;

    public ExampleProvider() {
        Injector.get().inject(this);
    }

    @Override
    public Iterator<Example> iterator(int first, int count) {
        List<Example> examples = exampleDao.find(first, count);
        Iterator<Example> exampleIterator = examples.iterator();
        return exampleIterator;
    }

    @Override
    public IModel<Example> model(Example object) {
        return Model.of(object);
    }

    @Override
    public int size() {
        return exampleDao.count();
    }
}

The html

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"  
      xmlns:wicket="http://wicket.apache.org"  
      xml:lang="en"  
      lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
</head>
<body>
    <wicket:extend>
        <table wicket:id="exampleTable" />
    </wicket:extend>
</body>
</html>

I tried just adding the sort parameter to the PropertyColumn so that the column would be clickable but
would not do anything.

columns.add(new PropertyColumn<Example>(Model.of("name"), "name", "name"));

This created the following error.

Last cause: null
WicketMessage: Exception in rendering component: [ [Component id = header]]

java.lang.NullPointerException
    at org.apache.wicket.extensions.markup.html.repeater.data.sort.OrderByLink$CssModifier.onComponentTag(OrderByLink.java:190)
    at org.apache.wicket.Component.renderComponentTag(Component.java:3885)
    at org.apache.wicket.Component.internalRenderComponent(Component.java:2506)
    at org.apache.wicket.MarkupContainer.onRender(MarkupContainer.java:1576)
    at org.apache.wicket.Component.internalRender(Component.java:2345)
    at org.apache.wicket.Component.render(Component.java:2273)
    at org.apache.wicket.MarkupContainer.renderNext(MarkupContainer.java:1474)
    ...

I have tried adding setSort(new SortParam(“name”, true)); to the Provider constructor

I have also attempted adding the complete backend to the DAO so that a sorted portion of the table would be returned.

I have also tried adding a field to the properties file for the page similar to the first resource sited at the bottom.

All of my attempts result in the same error. I think I must be missing something simple, but I have checked quite a few examples and found nothing.

The resources I have already checked include the following:

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1 Answer

  1. Editorial Team

    Don’t pass ‘null’ at new HeadersToolbar(exampleTable, null).

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