ChartRenderer Jsp refresh

Question

I have a chart using ChartRenderer data web bean in a Jsp deployed to tomcat. My chart works fine, but when the data changes making up the chart I have to resart the browser to refresh the chart. My BC4J view object used in the chart is based on a view (not table) which I create dynamically on the fly just before the chart is rendered. Any tips or tricks to have my chart display the refreshed data ??

Answer 1

Do you re-execute the viewObject's query?
This behavior can come from various sources:
1/ BC4J caching.
After a view object's query has been executed, its data is retrieved from the internal BC4J cache and not directly from the database.
-> In order to refresh the cache with current dataBase data, you should re-execute the appropriate view object's query (ViewObject.executeQuery()).
2/ Browser caching: your browser stores the rendered picture the first time it is requested and then gives you the stored picture in next requests instead of going all the way to the jsp.
-> In that case you have to include the proper pragma tags in your jsp in order to prevent your browser from caching the data/
<%
response.setDateHeader( "Expires", 0);
response.setHeader( "Pragma", "no-cache");
if( request.getProtocol().equals( "HTTP/1.1")) {
response.setHeader( "Cache-Control", "no-cache");
%>3/ Proxy caching: if your web server is accessed through a proxy, it can cache some pages as well.
-> I think the code above prevents proxy caching as well (not too sure about this though).
As you have already checked browser caching, It is likely that your problem lies with BC4J caching.
If I understand well, what's happening to you is: when you restart the browser, you lose your current JSP session, which holds the references to the appmodules used in this session.
Therefore, when you re-connect, the appModule pool looks for a free appModule instance to give you, most likely doesn't find one, and creates a new instance.
In this new instance, the view object's query hasn't been executed yet, therefore when you try to use it, the query is automatically executed, retrieving data from the database, and using it to populate this instance's cache.
Subsequent queries to the same appMod will retrieve data from the cache, as the viewObject's query has already been executed.
Hope this Helps, Remi
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