FlatRecordReader Class (Extends RecordReader)

Overview

The FlatRecordReader introduces only a few new attributes but has some new and overridden methods. It inherits several attributes and methods from its RecordReader and RecordHandler base classes (see Chapter 6).

Attributes:

• Integer Fixed Record Length

• Integer Record ID Field Offset

• Integer Record ID Field Length

Methods:

• Constructor

• getFieldValue

• getRecordType

• parseRecord

• readRecord

• readRecordFixedLength

Methods

Constructor

In the FlatRecordReader constructor method, we primarily retrieve values from the file description document that the reader needs for processing. The logic should look familiar by now.

Logic for the FlatRecordReader Constructor Method

Arguments:
  DOM Document File Description Document

Call RecordReader base class constructor, passing File
    Description Document
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"

getFieldValue

This method gets the complete value of a record's field with a single call. It is declared and implemented only in the FlatRecordReader class and isn't used in any of the other classes derived from the RecordReader class. The reason for this is that the other legacy formats (CSV and EDI) parse input records on a character-by-character basis. They save a field's characters to a DataCell object as they parse the record. In contrast, with the flat file format we parse records on a field-by-field basis, extracting fields from the record buffer based on offsets and lengths. This method is called from the FlatRecordReader's parseRecord method to perform that extraction. In addition, this method is designed to be used for extracting the record identifier, and until we have it we don't know how to parse the full record and load the DataCell Array.

The method is also called from the FlatRecordReader's testPartnerBreak method and the FlatRecordReader's getRecordType method. We call it for these special cases and not as a general purpose method for extracting field values from the input record buffer since in Java and C++ that operation takes only a couple lines of code. In addition to extracting the value, getFieldValue trims trailing whitespace and returns an error if the field is empty.

Logic for the FlatRecordReader getFieldValue Method

Arguments:
  Integer Field Offset
  Integer Field Length

Returns:
  Field value; throws exception or returns status

IF Field Offset > Record Buffer Length
  Return error
ENDIF
IF Field Offset + Field Length > Record Buffer Length
  Field Length <- Record Buffer Length - Field Offset
ENDIF
Field Value <- Extract from Record Buffer according to
    Passed Field Offset and adjusted Field Length
Field Value <- Trim trailing whitespace (<= ASCII space
    character)
IF length of Field Value = 0
  Return error
ENDIF
Return Field Value

getRecordType

This method extracts the value of the Record ID field from the input record buffer, trimming trailing whitespace. In the current implementation the field value is returned in its raw form, interpreted as alphanumeric string data.

Logic for the FlatRecordReader getRecordType Method

Arguments:
  None

Returns:
  Record ID tag value; throws exception or returns status

Record Tag Value <- call getFieldValue, passing Record ID Field
    Offset and Record ID Field Value
Return Record Tag Value or status

parseRecord

This method is not as interesting as the one in the CSVRecordReader because the grammar is not as complex. Essentially, we walk the FieldDescription Elements of the RecordDescription Element, extract the field contents according to their defined offsets and lengths, and create new DataCell objects.

Logic for the FlatRecordReader parseRecord method

Arguments:
  DOM Element Record Grammar

Returns:
  Error status or throw exception

Field Grammar NodeList <- call Record Grammar's
    getElementsByTagName for "FieldDescription"
DO until end of Field Grammar Node List
  Field Grammar Element <- Next item in Field Grammar NodeList
  Field Number <- call Field Grammar Element's getAttribute on
      "FieldNumber"
  Field Offset <- call Field Grammar Element's getAttribute on
      "Offset"
  Field Length <- call Field Grammar Element's getAttribute on
      "Length"
  IF Field Offset + 1 > Record Buffer Length
    Return success //  End of record
  ENDIF
  IF Field Offset + Field Length > Record Buffer Length
    Field Length <- Record Buffer Length - Field Offset
  ENDIF
  Field Length <- Record Buffer Length - Field Offset
  Field Value <- Extract from Record Buffer according to
      Field Offset and adjusted Field Length
  New Cell <- call RecordHandler's createDataCell method, passing
      Field Number and Field Grammar Element
  Call New Cell's putFieldValue method, passing Field Value
ENDDO

readRecord

This convenience method provides a way to protect calling routines from the variations in how we physically process records for flat files. It performs either a fixed or variable length read, depending on the physical characteristics gleaned from the file description document.

Logic for the FlatRecordReader readRecord Method

Arguments:
  None

Returns:
  Record Length or EOF

IF Fixed Record Length > 0
  Return call to readRecordFixedLength
ENDIF
Return call to base RecordReader's readRecordVariableLength

readRecordFixedLength

This method calls the language-specific routines for reading a fixed length record from a flat file.

Logic for the FlatRecordReader readRecordFixedLength Method

Arguments:
  DOM Element Record Grammar

Returns:
  Error status or throw exception

Clear Record Buffer
Record Buffer <- Call language-specific routine to read a fixed
    number of bytes from the input record stream
IF not EOF
  Return Fixed Record Length
ENDIF
Return EOF