A JasperReports Library data source (JRDataSource) is a Java class that contains the logic to retrieve data and feed it to the JasperReports Library process that generates a JRXML report. For example, you may write code to access a REST API and format the data. When using JasperReports Library natively in a Java environment, you must write the code to initialize your JRDataSource, for example any URLs or credentials needed to access the data.
JasperReports Server lets users enter the parameters for a data source and select which reports to run. When you want to use this same JRDataSource in the JasperReports Server environment, you must write additional classes and resources so that the server can do the following:
|•||At startup, register the data source so it can be selected by users.|
|•||When a user creates an instance of this data source, get its parameters from the user and store them in the repository.|
|•||When a user runs a report that uses this data source, instantiate and initialize the JRDataSource at runtime from the stored parameters. When the report is finished, clean up the JRDataSource object.|
|•||Optionally, if you have input controls for reports that use this data source, instantiate and initialize the JRDataSource again to process the query for input controls.|
Each of these actions are described in the following sections.
On startup, the Spring framework registers the custom data source definition with the custom report data source service factory in JasperReports Server. Users see the custom data source type on the Type menu in the New Data Source dialog, using the name defined in the message catalog.
When a user selects a custom data source type from the Type menu in the New Data Source dialog, they must enter values for any visible properties required to create the corresponding JRDataSource. Properties are specified in the Spring bean definition file, with labels defined in a message catalog (or bundle if you include translated messages for other locales). There may be additional hidden properties, set up in the Spring definition file.
When you create a custom data source, you can optionally implement validation for the property values in the New Data Source dialog. The logic for validation is defined by a Java class that implements the CustomDataSourceValidator interface. This class receives the user input, verifies it, and if necessary raises an error with strings defined in the message catalog.
Saving the data source instance creates a persistent object in the JasperReports Server repository.
When a user runs a report that uses the custom data source, the server instantiates the corresponding JRDataSource to access the data. This also happens when defining a Domain that uses the custom data source, when creating or running an Ad Hoc view based on a Domain that uses the custom data source, or when viewing a dashboard that includes any of these.
The JRDataSource is instantiated as follows:
|•||The custom data source instance is read from the repository and its data source definition is looked up by name.|
|•||An implementation of ReportDataSourceService is created and the properties from the repository are used to set the corresponding properties on the data source service.|
|•||A JRDataSource is created in one of two ways, depending on whether the data source uses a query:|
|•||If there is no query, the data source service has to provide the JRDatasource.|
|•||If there is a query, JasperReports Library creates a JRQueryExecuter of the correct class for the query language. The data source service passes any objects that the query executer needs by setting parameters. The JRQueryExecuter reads the parameters and produces the JRDataSource.|
|•||The JRDataSource is used to fill the report and produce a JasperPrint object, from which the server generates HTML or other supported output formats.|
A JasperReports Library data source is an implementation of the JRDataSource interface that provides data organized in rows and columns to the JasperReports Library filler. Each field declared in the JRXML corresponds to a column in the JRDataSource output.
The following figure shows the main steps in creating a JRDataSource from a custom data source instance.
JRDataSource Creation from Custom Data Source Instance
A query executer is an implementation of the JRQueryExecuter interface in the JasperReports Library. It interprets the queryString in the JRXML and produces a JRDataSource. JasperReports Library (either standalone or running in JasperReports Server) determines which query executer to use by looking at the language attribute of the queryString and looking up a query executer factory registered for that language.
JasperReports Server data sources can use two different methods to create a JRDataSource:
|•||The JasperReports Server data source can create a JRDataSource directly, without a queryString in the JRXML; or|
|•||The server can pass implementation-specific objects to the query executer through the report parameter map. The query executer then uses the objects from the parameter map, as well as the contents of the queryString, to create the JRDataSource.|
Selecting the method to use depends on the nature of the data source, as well as whether you want to use a queryString to control your data source. A good example of a data source using a query executer is the JDBC data source: it passes a JDBC connection to the JDBC query executer, which it uses to pass the SQL queryString to the database.
The samples demonstrate both methods:
|•||The custom bean data source creates a JRDataSource directly, which returns data from a hard-coded internal array. See Custom Bean Data Source.|
|•||The webscraper data source can either create a JRDataSource directly, using the properties supplied by the data source instance, or it can get those properties from a queryString in the JRXML. In this case, a data source instance isn’t required. The sample reports for this data source demonstrate each of these approaches. See Hibernate Custom Data Source.|