What is a Subreport
A Subreport is a JasperReports Template thats embedded within another JasperReports template (which we will refer to as the Master report).
As the Master report executes, each time the Subreport element is reached it is executed and its content seamlessly embedded into the output of the Master report.
The end result is a single output containing the blended contents of the Master report and each subreport execution.
Subreports can be nested.
When to Use Subreports
There are several situations when you wish to embed one report into other. Examples of such situations are:
- Isolating a common layout that is used in a series of reports
- Processing records from a query different from the Master report's query
This current example demonstrates the latter case.
Running the Sample
Prerequisites
Ant is required. By running 'ant --version' you will be able to check if ant is set up on your system (at least version 1.5 is required):
ant -version Apache Ant version 1.8.0 compiled on February 1 2010
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You can obtain ant from http://ant.apache.org/, instructions for installation can be found there as well.
Starting the Data Source
In a command prompt/terminal window browse to the demo/hsqldb folder of the JasperReports source and run the command 'ant runServer'.
Leave window/terminal running (see below for sample output).
ant runServer
Buildfile: C:\js-workspace\jasperreports\demo\hsqldb\build.xml
runServer:
[java] [Server@83cc67]: [Thread[main,5,main]]: checkRunning(false) entered
[java] [Server@83cc67]: [Thread[main,5,main]]: checkRunning(false) exited
[java] [Server@83cc67]: Startup sequence initiated from main() method
[java] [Server@83cc67]: Loaded properties from [C:\js-workspace\jasperreports\demo\hsqldb\server.properties]
[java] [Server@83cc67]: Initiating startup sequence...
[java] [Server@83cc67]: Server socket opened successfully in 19 ms.
[java] [Server@83cc67]: Database [index=0, id=0, db=file:test, alias=] opened sucessfully in 1104 ms.
[java] [Server@83cc67]: Startup sequence completed in 1125 ms.
[java] [Server@83cc67]: 2010-03-10 11:32:30.423 HSQLDB server 1.8.0 is online
[java] [Server@83cc67]: To close normally, connect and execute SHUTDOWN SQL
[java] [Server@83cc67]: From command line, use [Ctrl]+[C] to abort abruptly
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Generating the Report
Open up a separate command prompt/terminal window and browse to the root directory of the sample.
By running 'ant -p' you will be presented with a list of options available. Of interest in this list is all the exporters available for testing.
Each export type will generate a output type in the build/report folder.
By running the command 'ant' the following actions will be performed:
- All java code will be compiled to produce class files.
- JRXML fills will be compiled by JasperReports to produce a .jasperfile (this is a serialized version of a JasperReports object).
- The report will be filled with data and the resulting object, JasperPrint, will be serialized to the file system as a .jrprint.
- All the exporters the sample is configured to test will run.
You can now run 'ant view' to see a version of the report in the JasperViewer (an applet contained in the JasperReports package which can be used to view a .jrprint object).
Each of the these task can be ran separately as well:
- ant clean - removes all generated files.
- ant javac - compiles all java code, this should be done before running further tasks.
- ant compile - compiles the JRXML generating a .jasper file.
- ant fill - fills the report with data, some reports use the empty data source, others use the HSQL DB and other an inline data source. A .jrprint object is generated in this step.
- ant view - opens the report in the JasperViewer
- ant pdf - generates a PDF (other exporters are available run 'ant -p' for a full list)
Note: All generated files can be found in build/reports.
You now have a working version of the report you can review.
Configuring a Subreport
The first thing to note is any JasperReport can be used as a Subreport. However, once a report has embedded into another as a Subreport, the Master report is now responsible for:
- Supplying the Subreport with a JRDataSource
- Specifying an expression to locate the report design
- Passing Parameters into the Subreport
The Subreport can return data to the main report using variables.
In this example the Master Report contains the Address and Product reports embedded as Subreport elements.
Lets begin by review the configuration of the Subreport element for the Products Subreport.
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This element is in the Detail band of the Master report. This means this Subreport will be executed with each record in the Master report's Result Set.
subreportParameter
This tag indicates a Parameter in the Product report is being filled by the Master report. In this case, its the City field in the Master report
filling the City Parameter of the Product report.
If we look at the query of the Product report we see that the value of the City parameter is injected into the Query to constrain the Results:
What this means is the Product report executes for each row in the Master report's ResultSet and displays results related to the city field in that row
(Remember: Fields map to the data source, in this case to columns returned in the Result Set).
For more information on modifying report queries please view the Query Sample.
connectionExpression
This tag specifies the JRDataSource to be used to fill the subreport. In this case the built in parameter $P{REPORT_CONNECTION} is used.
This parameter contains a reference to JDBC Connection that was used to fill the Master Report. This is best practice when working with Subreports
which need to be filled with the same JDBC Connection as the Master report.
In situations where your Subreport doesn't use a data source (the report may just contain some text and/or images) a reference to the
JREmptyDataSource can be passed in here:
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returnValue
This tag indicates the value passed from the subreport to the Master report. The calulcation indicates if the value should be accumlated or just passed directly up.
In this case the calculation is Sum, meaning the PriceSum variable in the Subreport is going to be accumlated for each Subreport execution and stored in the
ProductTotalPrice variable of the master report. If the desired effect is to just pass a variable from the Subreport to the Master, then a calculation type of
None should be used.
subreport Expression
This tag indicates where the design of the Subreport can be located. Note the class. In this example the expression is returning a JasperReports object.
The subreport expression represents a very powerful place for extensions/integratoins. Ternary operators can be used here to load different Subreports based on different
conditions in the report. Also external Java classes can be called in this expression, provided they return a JasperReport reference, the subreport design can be obtained
or created using Java. In the SubreportApp.java the JasperReport reference is obtained by loading a .jasper (serialized JasperReport object) file from the file system.
Lets review the Address Report configuration.
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The main differences are here:
- returnValue: No calculation is set. The default is None, which means the variable REPORT_COUNT variable in the subreport will be passed directly to the Master.
- subreportExpression: In this case the expression class is a String and the expression is the location on the file system for the compiled version of the JRXML.
Is there performance concerns with Subreports?
The answer to this depends on your system, data source and your report design. A few points to note on Subreports:
- Each subreport execution may spawn a new thread (see below).
- As the subreport executes more objects will be created in Heap Memory.
On the subject of threads. Support for Java continuations has been added as an alternative to threads. This was done using the Jakarta Commons Javaflow library.
The JasperReports property: net.sf.jasperreports.subreport.runner.factory can be used with the following two settings:
- net.sf.jasperreports.engine.fill.JRContinuationSubreportRunnerFactory
- net.sf.jasperreports.engine.fill.JRThreadSubreportRunnerFactory
By default net.sf.jasperreports.engine.fill.JRThreadSubreportRunnerFactory is used, however if net.sf.jasperreports.engine.fill.JRContinuationSubreportRunnerFactory
is set, then a Javaflow approach will be used to fill the reports rather than threads. If this option is choosen, then the Jakarta Commons Javaflow jar must be
included in the application classpath. This jar can be found in the lib directory of the JasperReport reports project distribution package.
The jasperreports-javaflow.properties file illustrates how this property could be set in a actual implementation.
Other alternatives for processing different queries in the same report are usage of the List element and Sub Datasets.
Further Resources:
JasperReports Ultimate Guide (available from the JasperSoft eShop)
iReport Ultimate Guide (available from the JasperSoft eShop)