Java Reference
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We then proceed to call the readAll() method of CSVReader . This method reads the
contents of the CSV file and stores it into a java.util.List containing String arrays
as its elements. Each String array represents a row of values in the CSV file, mapping
them as they appear on the file. The List will have as many elements as there are
rows in the CSV file. The contents of our CSV file, AircraftData.csv , are as follows:
N912S,9973CC,PA18-150,R-1820 SER
After reading the contents of this CSV file, the CSVReader.readAll() method will
return a list containing four arrays of Strings:
{"N263Y", "T-11", "39 ROSCOE TRNR RACER","R1830 SERIES"}
{"N4087X", "BA100-163", "BRADLEY AEROBAT","R2800 SERIES"}
{"N912S", "9973CC", "PA18-150","R-1820 SER"}
As we can see, the layout corresponds to the layout of the CSV file just described.
JasperReports datasources contain 'elements' and 'fields'. When using a database as
a datasource, a database row is considered as an element, and the columns as fields.
When using Java objects as datasources, each object is an element, and each attribute
of the object is a field. For our custom CSV datasource, each row in the CSV file is
considered an element, and each column, a field.
The next() method defined in JRDataSource moves the cursor to the next element
in the datasource. It returns a Boolean, indicating if the move was successful or not.
In our implementation, we have a currentRowIndex variable, indicating the current
element in the List returned by CSVReader.readAll() method. In the next()
method, we increase the value of currenRowIndex by one, and return false if its
value is larger than the size of the list; otherwise, we return true .
The getFieldValue() method retrieves the value for the current field in the
datasource. It takes an instance of net.sf.jasperreports.engine.JRField class as
its only argument. The JRField interface contains a getName() method that is used
to retrieve the value of the field from its name. The way in which it is done depends
on the type of datasource. For example, JRBeanCollectionDataSource uses
utility classes from Jakarta commons-beanutils to retrieve the bean's property
value from its name. JRXmlDataSource uses a combination of Xalan , an XML
transformation library, and Jakarta commons for its implementation.
For our getFieldValue() implementation, since a CSV file does not map names to
its fields, we simply ignore the parameter. All we do is obtain the array of strings in
the List returned by CSVReader.readAll() corresponding to currentRowIndex .
We, then, obtain the field corresponding to currentColumnIndex from it.
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