XML to Flat File: Detail Design


Main Program

The shell main program functions are very similar to those of the XML to CSV converter.

Logic for the Shell Main Routine for XML to Flat
 Arguments:   Input Directory Name   Output Flat File Name   File Description Document Name Options:   Validate input   Help Validate and process command line arguments IF help option specified   Display help message   Exit ENDIF Open output file Create new FlatTargetConverter object, passing:     Output Stream     File Description Document Name Set up implementation dependent DOM environment for loading,     parsing, and validating input documents Open input directory Get first file from input directory DO for all files in input directory   Input Document <- Load input file, validating it if requested   Call FlatTargetConverter processDocument method, passing       the Input Document   Increment number of documents processed ENDDO Close output file Display completion message with number of documents processed 

FlatTargetConverter Class (Extends TargetConverter)

Overview

The FlatTargetConverter again is very similar to the CSVTargetConverter. However, like the FlatSourceConverter, we use a recursive algorithm to process the logical record groups in input documents. We use the base TargetConverter's processGroup method, described in this subsection.

Attributes:

  • None

Methods :

  • Constructor

  • processDocument

  • processGroup (base class method)

Methods
Constructor

The constructor method for our FlatTargetConverter object sets up that object and the FlatRecordWriter object.

Logic for the FlatTargetConverter Constructor Method
 Arguments:   Output Stream Flat Output file   File Description Document Name Call base class constructor, passing File     Description Document Name Create FlatRecordWriter object, passing:     File Description DOM Document and Output Stream 
processDocument

The bulk of the processing is performed in the FlatTargetConverter's processDocument and processGroup methods. This method converts one input XML Document and writes it to the flat file output stream based on the input parameters. Most of the actual work is done in the processGroup method.

Logic for the FlatTargetConverter processDocument Method
 Arguments:   DOM Document Input Document Returns:   Error status or throws exception Root Element <- Get Document's documentElement attribute Root Element Name <- Get Root Element's tagName attribute IF Root Element Name != Grammar Root Element Name   Return error ENDIF Call processGroup, passing Root Element and Grammar Element Return success 
processGroup (Base Class TargetConverter Method)

As with the processGroup method of the SourceConverter we use a recursive algorithm, but the details are a little bit different for the termination case. This method is used for both flat file and EDI conversions.

Logic for the FlatTargetConverter processGroup Method
 Arguments:   DOM Element Parent Element   DOM Element Group Grammar Returns:   Error status or throws exception Record Grammar Node <- Get firstChild from Grammar Element     skipping over non-Element Nodes Record Grammar Element <- Record Grammar Node //  Process the Group's starting Record Element Record Element <- Get first childNode from Parent Element,     skipping over non-Element Nodes Call RecordWriter's parseRecord, passing Record Element and     Record Grammar Element Call RecordWriter derived class's writeRecord, passing Record     Grammar Element // This advance makes sure that we don't repeat starting record //  in group Record Grammar Element <- Get next Record Element from     Group Grammar, skipping over non-Element Nodes Grammar Tag = call Record Grammar Element's getAttribute for     "ElementName" Record Element <- Get Record Element's nextSibling, skipping over     non-Element Nodes DO until all child Elements of Parent have been processed   Record Tag <- call Record Element's getNodeName   DO until Grammar Tag = Record Tag     Record Grammar Element <- Get next Record Element from         Group Grammar, skipping over non-Element Nodes     IF Record Grammar Element is NULL       Return error  //  This record is not part of the group     ENDIF   ENDDO   Grammar Element Name <- Call Record Grammar Element's       getNodeName   IF Grammar Element Name = "GroupDescription"     Call processGroup, passing Record Element and Record Grammar         Element   ELSE     Call RecordWriter's parseRecord, passing Record Element and         Record Grammar Element     Call RecordWriter derived class's writeRecord, passing         Record Grammar Element   ENDIF   Record Element <- Get Record Element's nextSibling, skipping       over non-Element Nodes ENDDO 

This method is called the first time from processDocument, which passes it the root Element of the Document and the complete Grammar Element. It processes the Element that represents the header record of the logical document, then advances to process its sibling records and groups. Record Elements are processed in the same fashion as the header record Element. Again, recall that in our XML representation of flat files a group of records is explicitly represented by an Element, with the group members (records or other groups) as child Elements. When we encounter an Element that represents a group (that is, when the Element's grammar Element has the name "GroupDescription"), we make a recursive call.

The termination cases are a bit different than those in the FlatSource Converter. In the XML representation the groups are explicitly represented, so we don't have a normal case of encountering an Element that isn't in the current group grammar. If we do hit one, this is an error; we return an error or throw an exception. For normal processing the method continues execution until all the Elements in the source document's group have been processed, then we return back to the caller.

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" 
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 


Using XML with Legacy Business Applications
Using XML with Legacy Business Applications
ISBN: 0321154940
EAN: 2147483647
Year: 2003
Pages: 181

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