Does Displaytag's ExcelView even work? Getting Non-Excel output of plain strings

Question

According to the Displaytag 1.2 documentation, ExportView is provided to output Excel files.

But actually, the source code shows that the entire Excel Model structure is just a plain data bean of strings. The result of using ExcelView to output an XLS is the following plain-text output (not a valid XLS),

"Agreement Category"    "Approving Official"    "Second Level Approving Official"   
"Regular"   "John Smith"    "Test"  

Indeed, the ExcelView Model package is just a String-based set of classes, like a POJO bean,

org.displaytag.model.Column
org.displaytag.model.HeaderCell
...

I understand that Displaytag also has a completely different renderer, org.displaytag.export.excel.DefaultHssfExportView , which uses HSSF to write XLS files. That renderer does produce a valid Excel file. (It's in the JAR displaytag-export-poi-1.2.jar.)

So what's the purpose of ExcelView, then? Is it a final renderer, or just an interface renderer of some kind? Does it assume more implementation? Why call it ExcelView if it doesn't actually output Excel, just a String list? Are we supposed to use DefaultHssfExportView for all Excel exports?

Answer 1

DisplayTag is a bad and poorly supported library, but here's what I've been able to find:

1. What it misleadingly calls org.displaytag.export.ExcelView is just a quote-enclosed String Renderer (they call it "ascii format, tab separated" ) At least one user thought it was CSV, but it's not, because there are no commas (CSV requires commas -- here it's just spaces and quotes: "test" "test2" etc.).

2. To actually output a real Excel file you need:

a) export.excel.class=org.displaytag.export.excel.DefaultHssfExportView in displaytag.properties

b) with: displaytag-export-poi-1.2.jar (this contains the DefaultHssfExportView),

c) with: poi-3.2-FINAL.jar This is very important. You can't use a higher POI version with DefaultHssfExportView.

This outputs a good Excel file, but there's one remaining problem: the current Page only (not the full List). Various ideas have been proposed to get the full List, such as using a different renderer called org.displaytag.export.excel.ExcelHssfView. This other renderer is also available in display-export-poi-1.2.jar but I get a ClassDefNotFound on it for some reason, and it can't be used. Only the DefaultHssfExportView renderer is found, instantiated, and works.

So for now I get a valid Excel file back, but with a Page-only set rather than the full set. There is no solution for the full set in the rendered XLS.

Answer 2

I was able to get the full binary Excel export with:

displaytag 1.2 and displaytag-export-poi 1.2

e.g. in build.gradle:

    implementation 'displaytag:displaytag:1.2'
    implementation 'displaytag:displaytag-export-poi:1.2'

and adding the following to displaytag.properties:

export.excel.class=org.displaytag.export.excel.ExcelHssfView