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Editorial Team
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Asked: 2026-05-26T18:19:01+00:00

JasperReports newbie here. I have read the tutorial and the quick reference and read

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JasperReports newbie here. I have read the tutorial and the quick reference and read up on a number of articles regarding JR, and have now been playing around with the iReport report designer for a day or so.

I think the last major set of concepts I am choking on have to do with the relationship between chart components and their data. Although it is easy to find definitions for each of these, there seems to be very little practicle documentation showing how they relate to one another in a meaningful application.

  • Report Fields
  • Report Prameters
  • Report Variables
  • Datasets

By playing around with iReport it seems that Fields, Parameters and Variables can exist at the report-level, as well as being placed inside of Datasets. But my understanding of when something is a Field vs. Parameter vs. Variable is very fuzzy, and my understanding of how they relate to Datasets is also very shaky.

Using Datasets as a slight segue, I’m having a tough time seeing the “forest through the trees” with how chart components (such as pie charts, tabls, etc.) get “fed” or “injected with” their data.

Soo… I thought of an example that, if answered, would tie everything together for me (I believe!). Let’s say I had two chart components, a text field and a pie chart. I want the pie chart to appear below the text field like so:

The author of this report is: <value supplied by the data source>

<pie chart here>

So, at “fill time” (I think I’m using that correctly…), the report will be “filled” with the name of the report’s author (a String), as well as a pie chart comprised of 2 pie slices: 1 slice with a value of 75 with a label/key of “Eloi” and a 2nd slice with a value of 25 and a label/key of “Morlocks”. If I am not using the correct JR terminology here, what I am trying to achieve is a fill-time pie chart with two slices: an “Eloi” slice consuming 75% of the chart, and a “Morlocks” slice consuming 25% of the chart.

If someone can explain or give code (Java/JRXML) snippets for how to set this kind of chart up, I think it will help connect all the dots and help me understand how components get filled with data. Thanks in advance for any and all help!

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1 Answer

  1. Editorial Team

    Think of parameters as things that the end user supplies to the report at runtime. For example, you supply a StartDate and an EndDate that will get used in a query. The start date that you are interested in is something you know, it’s not provided by the data source. (There are variations on this idea: maybe your application knows things about you based on your login, and it supplies these as parameters. But again, these are things known before the report is executed.)

    Think of the fields as the data that comes back from your data source. This is the stuff that you want to learn. For example, you run a query like this:

    select political_group, gullibility from mytable where the_date > $P{StartDate}

    Presumably you would input a value of ‘802701’ for the StartDate and then get results like this:

    $F{political_group} $F{gullibility}
Eloi                75
Morlock             25

    Think of variables as a way to manipulate this raw data. They can calculate totals and subtotals as well as line-by-line calculations like string manipulation or more complex things like running totals.

    Take a look at this pie chart report I posted a couple of years ago: http://mdahlman.wordpress.com/2009/05/02/limiting-pie-pieces/

    It has the main ideas you want. I put the title directly into the chart rather than as a separate field. That would be a very simple change. Likewise, you could change the title to “The author of this report is: $P{TheAuthor}” and then pass that param to the report at runtime.

    Using a field in the report title rather than a parameter is possible also. But typically it doesn’t make sense. The fields will have many values in the data set. Which one belongs in the title? In the case above “Eloi” and “Morlock” are fields, and they really don’t make sense in the report title. (You can imagine special cases, of course. You could concatenate all of the political_group values into a single string and put that in the report title. But in an overwhelming majority of cases this won’t be reasonable.)

    Good luck.

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