export.apt

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                                    ------------------------------
                                           Exporting data
                                    ------------------------------
                                          Fabrizio Giustina
                                    ------------------------------
                                              11-11-2005
                                    ------------------------------


Exporting data

   When you set the Table Tag's export attribute to "true", a footer
   will appear below the table which will allow you to export the data
   being shown in various formats.

   Displaytag includes a few ready made export views which allow you to
   export data in CSV, excel, and XML format. A simple PDF export view
   is also available. The following table lists the predefined export
   options included in displaytag distribution.

*-----------------+----------------------------------------+-----------------------------------------------------------+
|  Media          | Export View Class                      | Description                                               |
*-----------------+----------------------------------------+-----------------------------------------------------------+
|  CSV            | org.displaytag.export.CsvView          | Export to comma separated list                            |
*-----------------+----------------------------------------+-----------------------------------------------------------+
|  Excel          | org.displaytag.export.ExcelView        | Export to excel - ascii format, tab separated             |
*-----------------+----------------------------------------+-----------------------------------------------------------+
|  XML            | org.displaytag.export.XmlView          | Simple xml output                                         |
*-----------------+----------------------------------------+-----------------------------------------------------------+
|  PDF            | org.displaytag.export.PdfView          | Sample PDF export view                                    |
|                 |                                        | Not enabled by default, set export.pdf=true in            |
|                 |                                        | displaytag.properties and including the required          |
|                 |                                        | IText jar in WEB-INF/lib                                  |
*-----------------+----------------------------------------+-----------------------------------------------------------+


* Configuring export and export views

   The export.types parameter contains the list of registered export
   views. For each export type you can configure other parameters: see
   the export. exportname.* parameters in {{{configuration.html}configuration}}.

   You can enable/disable a specific export type using the export.
   exportname.enabled parameter.

   If you don't want some column to show during export (or you only
   want them to show during export) you can use the column media
   attribute (see tag reference for more details).

* Adding a new Export view

    1. Write your own exportView class. You need to implement the
       org.displaytag.export.TextExportView or
       org.displaytag.export.BinaryExportView interface. You can look
       at the {{{displaytag/xref/org/displaytag/export/PdfView.html}sample binary PDF export view}} or to
       {{{displaytag/xref/org/displaytag/export/BaseExportView.html}the base text export view}} used by displaytag.

    2. Add a displaytag.properties file in your application classpath
       (if you already don't have one) and add the name of your export
       media along with the default ones to the export type parameter:
       <<<export.types=csv excel xml [mymedia]>>>

    3. Always in displaytag.properties , add the following properties:

+------------------------------------------------------------------------------+
export.[mymedia]=true

export.[mymedia].class=fully.qualified.class.name

export.[mymedia].label=Click here to try my export

# include header parameter is forwarded to your export view
export.[mymedia].include_header=true

# if set, file is downloaded instead of opened in the browser window
export.[mymedia].filename=
+------------------------------------------------------------------------------+

    4. Try it. You should see a new link with the text you added to
       export. mymedia .label . Clicking on it will invoke your Export
       view. You should see the results in your browser.

* Text/Binary export views

   Common displaytag export options (CSV, Xml and Excel) output a
   simple text-based format. Other file formats require binary content,
   like the sample PDF included with the distribution.

   Exporting binary data from a JSP is a bit tricky, since JSPs are
   only designed to output characters: as a starting point keep in mind
   that binary export is not assured to work on every application
   server , at least without the help of an external filter (see
   {{{export_filter.html}export filter}}).

   It may work without a filter if your application server allows JSPs
   to call response.getOutputStream() , but this method really
   shouldn't be used in JSPs. Using an the export filter, especially in
   buffered mode, could solve the problem, since the output stream is
   requested by the filter outside the JSP.