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(VB.NET UWP/WinRT) Efficiently Process a Huge XML File
Demonstrates a technique for processing a huge XML file (can be any size, even many gigabytes).
Note: This example requires Chilkat v184.108.40.206 or greater.
' This example shows a way to efficiently process a gigantic XML file -- one that may be too large ' to fit in memory. ' ' Two types of XML parsers exist: DOM parsers and SAX parsers. ' A DOM parser is a Document Object Model parser, where the entire XML is loaded into memory ' and the application has the luxury of interacting with the XML in a convenient, random-access ' way. The Chilkat Xml class is a DOM parser. Because the entire XML is loaded into memory, ' huge XML files (on the order of gigabytes) are usually not loadable for memory constraints. ' A SAX parser is such that the XML file is parsed as an input stream. No DOM exists. ' Using a SAX parser is generally less palatable than using a DOM parser, for many reasons. ' ' The technique described here is a hybrid. It streams the XML file as unstructured text ' to extract fragments that are individually treated as separate XML documents loaded into ' the Chilkat Xml parser. ' ' For example, imagine your XML file is several GBs in size, but has a relatively simple structure, such as: ' ' <Transactions> ' <Transaction id="1"> ' ... ' </Transaction> ' <Transaction id="2"> ' ... ' </Transaction> ' <Transaction id="3"> ' ... ' </Transaction> ' ... ' </Transactions> ' In the following code, each <Transaction ...> ... </Transaction> ' is extracted and loaded separately into an Xml object, where it can be manipulated ' independently. The entire XML file is never entirely loaded into memory. Dim fac As New Chilkat.FileAccess Dim success As Boolean = fac.OpenForRead("qa_data/xml/transactions.xml") If (success = False) Then Debug.WriteLine(fac.LastErrorText) Exit Sub End If Dim xml As New Chilkat.Xml Dim sb As New Chilkat.StringBuilder Dim firstIteration As Boolean = True Dim retval As Integer = 1 Dim numTransactions As Integer = 0 ' The begin marker is "XML tag aware". If the begin marker begins with "<" ' and ends with ">", then it is assumed to be an XML tag and it will also match ' substrings where the ">" can be a whitespace char. Dim beginMarker As String = "<Transaction>" Dim endMarker As String = "</Transaction>" While retval = 1 sb.Clear() ' The retval can have the following values: ' 0: No more fragments exist. ' 1: Captured the next fragment. The text from beginMarker to endMarker, including the markers, are returned in sb. ' -1: Error. retval = fac.ReadNextFragment(firstIteration,beginMarker,endMarker,"utf-8",sb) firstIteration = False If (retval = 1) Then numTransactions = numTransactions + 1 success = xml.LoadSb(sb,True) ' Your application may now do what it needs with this particular XML fragment... End If End While If (retval < 0) Then Debug.WriteLine(fac.LastErrorText) End If Debug.WriteLine("numTransactions: " & numTransactions)
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