tut_links.apt

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                                    ------------------------------
                                          Generating links
                                    ------------------------------
                                          Fabrizio Giustina
                                    ------------------------------
                                              11-11-2005
                                    ------------------------------

Generating links

* Smart linking of column data

   If you have email addresses or web URLs in the data that you are
   displaying in columns of your table, then you can set the
   autolink="true" attribute in your display:column tag, and that will
   tell the display:table to automatically display those pieces of data
   as hyperlinks, you will not have to take any action to convert that
   data.

     * Email addresses will be wrapped with a <<<\<a href="mailto:xxx"\>xxx\</a\>>>> tag, where "xxx" is the email address
       that was detected.

     * Web URLs will be wrapped with a <<<\<a href="xxx"\>xxx\</a\>>>> tag, where
       "xxx" is the URL that was detected (it can be any valid URL
       type, http://, https://, ftp://, etc...)

     []

   If your column data has additional text, only the data that appears
   to be an email address or a URL will be linked (not the entire
   column).

   Turning on autolink does carry a performance penalty, as each string
   has to be scanned for patterns and updated if it matches on an
   address or URL.


* Dynamic links

   There are two ways to create dynamic links that should appear in a
   column. The first method is a "struts-like" approach which works
   well if the link you want to create is based on just a single
   property of the object being displayed (like a primary key value).
   The second approach makes use of decorators as described on the
   previous example. A decorator should be used when the dynamic link
   being created relies on multiple pieces of information, relies on
   the index of the object in the list, relies on some other data
   around it, or you want to change the text that is linked (ie you
   want it to say "edit", instead of showing the primary key of the
   object). Below I show how to use both examples.

* Struts-like approach

   The column tag provides 5 struts-like attributes that can be set to
   create a dynamic linke ( href, paramID, paramName, paramProperty,
   paramScope ). See the display:column documentation, and the struts
   documentation for a complete description of their usage, but
   basically:

   [href] the base URL used to construct the dynamic link

   [paramId] the name of the parameter that gets added to the URL specified above

   [paramName] name of the bean that contains the data we want to tack on the the URL (typically null, indicating the current object in the List)

   [paramProperty] property to call on the object specified above to return the value that gets tacked onto the URL.

   [paramScope] specific scope where the databean lives, typically null


   Of these params, you typically would not use paramName and
   paramScope. Leaving each as null indicates that you want to use the
   object corresponding to the current row being processed.

+-------------------------------------------------------------------+
<display:table name="sessionScope.details">
  <display:column property="id" title="ID" href="details.jsp" paramId="id" />
  <display:column property="email" href="details.jsp" paramId="action" paramName="testparam" paramScope="request" />
  <display:column property="status" href="details.jsp" paramId="id" paramProperty="id" />
</display:table>
+-------------------------------------------------------------------+


* Using a decorator

   The previous example page introduced the decorator to format dates,
   money, etc... It can also be used to create dynamic links on the fly
   so that you can either click on a particular column value and "drill
   down" for more information, or you can create a column of text
   labels which are hyperlinks that perform some action on the object
   in that row.

   These dynamic links can be created based on some primary key of the
   object, or they can make use of the object List index.

   Below is a table that has two columns that have hyperlinks created
   on the fly, the first makes use of the object's "ID" field to show
   additional details about that object, while the second makes use of
   the object's row index value to do basically the same thing.

   Here you can see the details of the getLink1() and getLink2()
   methods in the sample TableDecorator

+-------------------------------------------------------------------+
public String getLink1()
{
        ListObject lObject= (ListObject)getCurrentRowObject();
        int lIndex= getListIndex();
        return "\<a href=\"details.jsp?index=" + lIndex + "\"\>" + lObject.getId() + "\</a\>";
}


public String getLink2()
{
        ListObject lObject= (ListObject)getCurrentRowObject();
        int lId= lObject.getId();

        return "\<a href=\"details.jsp?id=" + lId + "&amp;action=view\">View&lt;/a> | "
                + "&lt;a href=\"details.jsp?id=" + lId + "&amp;action=edit\">Edit\</a> | "
                + "\<a href=\"details.jsp?id=" + lId + "&amp;action=delete\">Delete\</a>";
}
+-------------------------------------------------------------------+


+-------------------------------------------------------------------+
<display:table name="sessionScope.details" decorator="org.displaytag.sample.Wrapper" >
  <display:column property="link1" title="ID" />
  <display:column property="email" />
  <display:column property="link2" title="Actions" />
</display:table>
+-------------------------------------------------------------------+