Swift

Efficiently Process a Huge XML File

See more XML Examples

Demonstrates a technique for processing a huge XML file (can be any size, even many gigabytes).

Note: This example requires Chilkat v9.5.0.80 or greater.

Swift

func chilkatTest() {
    var success: Bool = false

    // 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.

    let fac = CkoFileAccess()!

    success = fac.open(forRead: "qa_data/xml/transactions.xml")
    if success == false {
        print("\(fac.lastErrorText!)")
        return
    }

    let xml = CkoXml()!
    let sb = CkoStringBuilder()!
    var firstIteration: Bool = true
    var retval: Int = 1
    var numTransactions: Int = 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.
    var beginMarker: String? = "<Transaction>"
    var endMarker: 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(startAtBeginning: firstIteration, beginMarker: beginMarker, endMarker: endMarker, charset: "utf-8", sb: sb).intValue
        firstIteration = false

        if retval == 1 {
            numTransactions = numTransactions + 1
            success = xml.loadSb(sb: sb, autoTrim: true)
            // Your application may now do what it needs with this particular XML fragment...
        }

    }

    if retval < 0 {
        print("\(fac.lastErrorText!)")
    }

    print("numTransactions: \(numTransactions)")

}