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>