Lessons in Jasper (i)Reports

I had some great fun today playing around with iReport. I used Dynamic Jasper before iReport so it was an interesting experience seeing the platform first hand and seeing all the capabilities it offered via the properties panels in iReport for the various report components. It was interesting to see the layout capabilities of a Jasper report and how Dynamic Jasper worked with these. ¬†A quick refresher, a Jasper report is split into different bands: Title, Page Header, Column Header, optional group headers, various detail bands, optional group footers, optional column footer, Page Footer, Last Page Footer, Summary, a No Data and a Background band. DJ follows closely to the Jasper specification & its capabilities. There are some things it can do better than iReport and some it cant. ¬†The most obvious DJ benefit is the programatic table layouts, which is all through code and means your dependent properties are known in advance when you refactor a business class – you should be able to know when your report is going to break. ¬†One issue I’ve had with DJ is that laying out components doesn’t always happen as beautifully as you’d expect. ¬†Sometimes the width of columns totals is too small with unexplained wrapping or sometimes the layout is just wierd. ¬† And there is no way of knowing until runtime that the seemingly simple change has broken the layout of your wonderful report. iReport on the other hand is comprised of datasources, sql or xml, and a jrxml template you design. ¬†You aren’t fixed into a particular table structure, you can have multiple group variables on the same field without any kind of reprocrussions and the WYSIWYG editor and preview allows you to quickly play with report layout and styles and know what you are getting. ¬†You can also start with a SQL query as your datasource to prototype and then at runtime inject a proper JRDataSource (the same DynamicJasper uses) – easy! But in the end of the day both of these compile down to .jasper files that Jasper Reports then fills in with your data and turns into these jrprint files – effectively a softcopy of your final report that you can turn into PDF or feed into a screen viewer.

Column Headers above Group Headers

One neat feature that Dynamic Jasper provides is the ability to put the column labels in a tabular format report below the group label via its setGroupLayout() method. I didn’t realise that the only thing that Jasper supports is having a column header band above the group header band. So in iReport, this means you cant have group title followed by the column headers. The way around this in iReport is that in your Group Header, you move the column headers into the last Group Header band you want. ¬†That way each time the group header gets displayed, so too will your Column header, underneath the Group label.

SubReports for non-data areas

The other trick I learnt was that when generating subreports that dont normally have data in them, for example a Header and Footer section, you need to be change the subreports ‘When No Data’ value to something like ‘All Sections, No Detail’ so that it doesnt simply show a blank page when you preview it and include it in a master report.

One thing that doesn’t work is that you can’t put the total page count in a subreport since its evaluated at report completion time and the subreport is already processed by the time its done.

You can’t do that on Television

Layout wise the iReport stuff really starts taking a big lead over DJ. ¬†The biggest case in point was the Sales Report dashboard demo that shows a 2 x 2 panel dashboard with a graph, table, pie chart and timeline chart. ¬†The right column isn’t as wide as the left¬†and there are also some neat tricks about using the REPORT_COUNT variable thats in each jasper report to limit the size of the dataset to do Top 5, Top 10 style reports. ¬† The video is worth watching just so you know some other little tricks. ¬†For example a foreground alpha channel percentage setting that gives pie charts a futuristic look is worth knowing about.

Pain in the bum Error Messages

Here DJ is better than iReport. ¬† One frustrating experience I had with iReport is an error message about an expression with unexpected ‘+’ token. ¬†I looked through all the expression fields I could find, searched the XML but couldnt find the place it was talking about. ¬†In the end I started the report again from scratch and slowly recreated the components from the old one trying to eliminate which was the problematic component. ¬†One thing that I noticed in the screencasts is that the designers use the Preview button frequently after any change that introduces a new variable, param or field, or datasource, or whatever. ¬†There are a lot of silent traps you can get into and therefore a lot of checks you need to do across the way. Dynamic Jasper is a bit better since

  1. you are limited in what you can do somewhat, you aren’t generally going to get a compile error,
  2. the error messages are a little clearer but not always,
  3. you have the source code and its a little easier to understand.


iReport and DJ both offer various views into the Jasper Reports framework.  Its certainly knowing both.  Since you can combine them, you can use iReport to do the complicated formating and embed DJ reports.




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