FlatRecordWriter Class (Extends RecordWriter)
Overview
As is the case with the CSVRecordWriter class, the FlatRecordWriter is derived from the RecordWriter base class (see Chapter 6). The most important method developed in this class is the writeRecord method. We use the parseRecord method inherited from the RecordWriter base class.
Attributes:
Integer Fixed Record Length
Integer Record ID Field Offset
Integer Record ID Field Length
Methods:
Constructor
writeRecord
Methods
Constructor
The logic for the FlatRecordWriter constructor method is essentially the same as that for the FlatRecordReader.
Logic for the FlatRecordWriter Constructor Method
Arguments:
DOM Document File Description Document
Output Stream
Call RecordWriter base class constructor, passing File
Description Document and Output Stream
Record Format Element <- Get "RecordFormat" Element from File
Description Document
Child Element <- Get first childNode from Record Format Element,
advancing over non-Element Nodes
Fixed Record Length <- 0
IF Child Element NodeName = Fixed
Fixed Record Length <- Call Child Element's getAttribute for
"Length"
ELSE
Record Terminator <- Call Child Element's getAttribute for
"RecordTerminator"
Call setTerminator to set the Record Terminators
ENDIF
Tag Info Element <- Get "RecordTagInfo" Element from File
Description Document
Record ID Field Offset <- Call Tag Info's getAttribute for
"Offset"
Record ID Field Length <- Call Tag Info's getAttribute for
"Length"
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writeRecord
The writeRecord method handles the aspects of record formatting unique to each legacy format. We should again note two restrictions mentioned at the beginning of the chapter. The record identifier field will be converted if it is present in the input XML document, but the value will be overridden by the value specified in the grammar. If a fixed record length is specified the record is initialized to ASCII spaces. Variable length records are initialized with the null character.
The approach for writing a record to flat files is somewhat different than the approach we used for writing to CSV files. For CSV files we walked through the DataCell Array and built the output buffer from its contents. Column number was key, and if a column was missing, a column delimiter was inserted. Due to the requirement to fill missing fields with a default fill character, we must take a different approach and drive the conversion from the record grammar instead of the contents of the DataCell Array. We will cycle though the FieldDescription Elements of the RecordDescription, find matching fields in the DataCell Array, and build the output buffer accordingly. If a field in the grammar is not present in the DataCell Array built from the input, we fill it using the fill character specified in the grammar.
Logic for the FlatRecordWriter writeRecord Method
Arguments:
DOM Element Record Grammar
Returns:
Error status or throws exception
IF Fixed Record Length > 0
Initialize Output Record Buffer to null characters
ELSE
Initialize Output Record Buffer to ASCII spaces
ENDIF
Record Length <- 0
Cell Array Index <- 0
Field Grammar NodeList <- Call Record Grammar's
GetElementsByTagName for "FieldDescription"
DO for all items in Field Grammar NodeList
Field Grammar Element <- next item from Field Grammar NodeList
Grammar Field Number <- call Field Grammar Element's
getAttribute for "FieldNumber"
Offset <- Call Grammar Element's getAttribute for "Offset"
Length <- Call Grammar Element's getAttribute for "Length"
Field Written <- false
IF (Index <= Highest Cell)
Field Number <- call CellArray[Index] getFieldNumber
IF (Field Number = Grammar Field Number)
Call CellArray[Index] fromXML
Call CellArray[Index] prepareOutput
Field Contents <- Call CellArray[Index] getField
Output Buffer <- Insert Field Contents at Offset for Length
Clear CellArray[Index]
Increment Cell Array Index
Field Written <- true
ENDIF
ENDIF
IF ( Field Written = false)
Fill Character <- Call Grammar Element's getAttribute for
"FillCharacter"
Output Buffer <- Insert Fill Character at Offset for Length
ENDIF
Working Length <- Offset + Length
IF (Working Length > Record Length)
Record Length = Working Length
ENDIF
ENDDO
Highest Cell <- -1
Record ID Value <- Call Record Grammar Element's getAttribute
for "TagValue"
Output Buffer <- Insert Record ID Value at Record ID Field
Offset for Record ID Field Length
IF Fixed Record Length = 0
Append base RecordHandler's Record Terminators to Output
Buffer
Increment Record Buffer Length
ENDIF
Call language's write routines to do physical write of
Output Buffer for Record Length
Return success
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