ExcelExport doesn't populate column headers in Excel file 
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                 Key: TOMAHAWK-911
                 URL: https://issues.apache.org/jira/browse/TOMAHAWK-911
             Project: MyFaces Tomahawk
          Issue Type: Bug
    Affects Versions: 1.1.5-SNAPSHOT
         Environment: Tomahawk 1.1.5-SNAPSHOT and Sandbox 1.1.5-SNAPSHOT
            Reporter: Tara Peltier


See posting on mailing list:
http://www.nabble.com/ExcelExport-column-headers-in-Excel-file-tf3302286.html#a9185916

Body of posting pasted here:

I have found two areas where the behavior is unexpected, perhaps bugs?

1) If the dataTable has sortable=true, then none of the column headers get 
exported at all.

2) If the column header uses a value-binding, it does not get exported to the 
Excel worksheet in the first row.  If the column header doesn't use a 
value-binding, then the column header does get exported to the Excel worksheet.
-----------------------------------------------------------
Here's more details, as I downloaded the source for ExcelExport and debugged 
into it, and I believe I have identified the problem area(s).

Problem 1)
In ExcelExportPhaseListener, the following method is used to convert each 
"cell" in the datatable into a value for the Excel spreadsheet.
private void addColumnValue(HSSFRow rowHeader, UIComponent component, int 
index) {
                HSSFCell cell = rowHeader.createCell((short)index);
                cell.setEncoding(HSSFCell.ENCODING_UTF_16);
                if(component instanceof ValueHolder) {
                        String stringValue = 
RendererUtils.getStringValue(FacesContext.getCurrentInstance(), component);
                        cell.setCellValue(stringValue);
                }
        }

When sortable=false on the datatable, the component passed to addColumnValue is 
of type HtmlOutputText.  However, when sortable=true on the datatable, Tomahawk 
automatically wraps each column with a sortable header and so the component 
presented to ExcelExport is of type 
org.apache.myfaces.custom.sortheader.HtmlCommandSortHeader.   This fails the 
"if(component instanceof ValueHolder)" check and so doesn't even try to get the 
value from the column.


Problem 2)
The problem revolves around the following line from the method pasted above 
(ExcelExportPhaseListener.addColumnValue):
String stringValue = 
RendererUtils.getStringValue(FacesContext.getCurrentInstance(), component);

If the column header is defined without using a value binding then the 
following line in ExcelExportPhaseListener.addColumnValue is evaluated 
correctly and returns the expected value.
E.g., for a column header like this
<t:column>
  <f:facet name="header"><h:outputText value="TEST COLUMN NAME" /></f:facet>
  <h:outputText value="#{trans.id}" />
</t:column>
the value evaluted by String stringValue = 
RendererUtils.getStringValue(FacesContext.getCurrentInstance(), component); is 
"TEST COLUMN NAME"
and the generated Excel file contains TEST COLUMN NAME in the first row.

However, if the column header is defined with a value binding (to a messages 
file for example) then the following line in 
ExcelExportPhaseListener.addColumnValue is evaluated incorrectly and returns an 
empty string.
E.g., for a column header like this
<t:column>
  <f:facet name="header"><h:outputText value="#{messages.trans_id}" /></f:facet>
  <h:outputText value="#{trans.id}" />
</t:column>
the value evaluted by String stringValue = 
RendererUtils.getStringValue(FacesContext.getCurrentInstance(), component); is 
""  and the generated Excel file contains an empty string in the first row.





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