How to modifiy the empty value of a column in displaytag?

Question

If a column's value is null, DisplayTag prints an empty String. Here is the source code doing that in the org.displaytag.model.Column#getValue method :

if (object == null || "null".equals(object)) //$NON-NLS-1$
{
    if (!this.header.getShowNulls())
    {
        object = TagConstants.EMPTY_STRING;
    }
}

I'm wondering if there is a way to override that and display a specific value rather than empty String. What I'm looking for is a generic/automatic solution because otherwise I could handle that manually by testing if my attribute corresponding to the column is null and returning the specific character if needed...

Answer 1

You can use a Decorator to customize the value of any column as required:

Examples

http://demo.displaytag.org/displaytag-examples-1.2/example-decorator.jsp

Tag Reference:

http://www.displaytag.org/10/tagreference-displaytag-12.html

Thus create a class:

public class MyCustomColumnDecorator implements DisplaytagColumnDecorator{

    public Object decorate(Object columnValue, PageContext pageContext, MediaTypeEnum media) {
        return value == null ? "some string" : value;
    }
}

Specify this in your markup for any column you wish to use it for:

<display:table name="someList">
  <display:column sortable="true" title="ID"/>
  <display:column property="email" autolink="true"/>
  <display:column property="description" title="Comments" decorator="com.test.MyCustomColumnDecorator"/>
</display:table>