JSF dataTable dynamic columns Problem

Question

Hello everybody,
I'm trying to display a table with a dynamic number of columns. I found only 1 topic on the matter and tried it out.
The JSP Page has this tag:
<h:dataTable      binding="#{ViewBean.dataTable}"
     value=     "#{ViewBean.tableRows}"
     var=     "#{row}" />
My "viewBean" contains the following code:
In constructor:
dataTable = new UIData();
//This one contains a simple list of 10 integers so that 10 rows are rendered, just for testing.
public ArrayList getTableRows ()
     ArrayList lst = new ArrayList();
     for (int n=0; n<10; n++) {
     lst.add(new Integer(n));
     return lst;
//Now my databinding thingy:
public UIData getDataTable()
UIColumn col;
UIOutput out = null;
Application app = app = FacesContext.getCurrentInstance().getApplication();
int colCount = 3;
     for(int j = 0; j < colCount; ++j) {
out = new UIOutput();
col = new UIColumn();
ValueBinding vb = app.createValueBinding("#{" + j + "}"); //just a simple expression with nothing difficult in it.
out.setValueBinding("value", vb);
out.setRendererType("Text");
col.getChildren().add(out);
dataTable.getChildren().add(col);
     return dataTable;
Now the error I get:
[com.sun.faces.el.ValueBindingImpl] getValue(ref=ViewBean.tableRows)
[com.sun.faces.el.VariableResolverImpl] resolveVariable: Resolved variable:biz.mbisoftware.ep.view.ListView@ee0373
[com.sun.faces.el.ValueBindingImpl] getValue Result:[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[com.sun.faces.el.ValueBindingImpl] -->Returning [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
[com.sun.faces.renderkit.html_basic.HtmlBasicRenderer] Begin encoding component _id2
[com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer] component.getValue() returned Name
[com.sun.faces.renderkit.html_basic.HtmlBasicRenderer] Value to be rendered Name
[com.sun.faces.renderkit.html_basic.ButtonRenderer] Begin encoding children _id0
[com.sun.faces.renderkit.html_basic.HtmlBasicRenderer] Begin encoding component _id3
[com.sun.faces.el.ValueBindingImpl] getValue(ref=1)
[com.sun.faces.el.ValueBindingImpl] getValue Result:1
[com.sun.faces.el.ValueBindingImpl] -->Returning 1
[com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer] component.getValue() returned 1
[com.sun.faces.application.ApplicationImpl] Created converter of type javax.faces.convert.LongConverter
[com.sun.faces.renderkit.html_basic.HtmlBasicRenderer] Value to be rendered 1
[com.sun.faces.taglib.html_basic.DataTableTag] id: null class: com.sun.faces.taglib.html_basic.DataTableTag
java.lang.NullPointerException
...long traceback...
Anyone has an idea what happened, or why it's not working? I have no clue.
Thx for your time.
Bjoern

Answer 1

Hello derBjoern,
First off, it's not valid to have an expression in the value of the var
attribute. "var" should just be a String.
Secondly, there are some typos in your sample, perhaps these were
introduced during posting to the forum, but I had to remove them to get
it to run for me.
* "app = app ="
* There is no "Text" renderer type in the standard RenderKit. The
proper name is "javax.faces.Text". (The error message is terrible
here).
Once I did that. It worked using the latest build from java.net.
Here is the revised getDataTable() method.
public UIData getDataTable()
     UIColumn col;
     UIOutput out = null;
     Application app = FacesContext.getCurrentInstance().getApplication();
     int colCount = 3;
     for(int j = 0; j < colCount; ++j) {
     out = new UIOutput();
     col = new UIColumn();
     ValueBinding vb = app.createValueBinding("#{" + j + "}"); //just a simple expression with nothing difficult in it.
     out.setValueBinding("value", vb);
     out.setRendererType("javax.faces.Text");
     col.getChildren().add(out);
     dataTable.getChildren().add(col);
     return dataTable;
The output I received was:
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
0      1      2
Ed (JSR-252 Spec co-lead)