Output Restrictions and Requirements

In Section 5.1, we defined a number of methods that write HTML code to a java stream. This code will then be returned to a portlet client and displayed inside the portal framework. Depending on the implementation of the portal framework, there may be restrictions on what HTML tags can be included in the output. The following lists the output restrictions for portlets built using the Jetspeed portal framework [17].

• Jetspeed uses tables to format the layout of the portal. Therefore, the output that is returned by our xbook will be displayed inside one of the table cells. Thus, any HTML tags written to the portlet should be tags that are valid inside a table cell (i.e., body tags only). The xbook should not write any header tags (e.g., HTML, HEAD, TITLE) nor the BODY tag.

• Our portlet client is a subclass of VelocityPortlet which allows our portlet client to be plugged into Jetspeed. The VelocityPortlet is also form-based and therefore places our xbook output inside its own specially formatted FORM tags. Therefore, our xbook output should not contain FORM tags, only input tags.

Our xbook portlet also impose some additional restrictions:

• Input tags written by the xbook (i.e., xbook variables) need to be differentiated from internal Jetspeed input variables and internal xbook input variables. Therefore, we impose a naming restriction on the xbook input variables. A xbook variable's name must be prefixed with 'xbook.form.'. If a xbook input tag does not have this special prefix, it will be ignored by the portlet and thus the value will not be returned back to the xbook.

• As discussed in Section 3.2.3, the xbook portlet determines whether a xbook session is complete by checking the value of a variable called xbooks.keep_alive. Therefore, the xbook must write a hidden input tag which has a boolean value. True or '1' indicates that the xbook session is still active and the portlet should expect more output to come.

          <input type="hidden" name="xbooks.keep_alive" value="1">
  

  While false or '0' indicates that this is the last output and the portlet can shutdown the xbook manager.

          <input type="hidden" name="xbooks.keep_alive" value="0">
  

• As described in Section 5.1, each xbook form must name the doXXX routine that will handle the input values. The xbook portlet reads in the name of the xbook method name from the form variable xbooks.action. Thus, if the user creates a method called doSubmit, they would express this in a hidden input tag as follows:

          <input type="hidden" name="xbooks.action" value="Submit">