preserve formatting when updating xml file with groovy

I have a large number of XML files that contain URLs. I'm writing a groovy utility to find each URL and replace it with an updated version.

Given example.xml:

<?xml version="1.0" encoding="UTF-8"?>
<page>
    <content>
        <section>
            <link>
                <url>/some/old/url</url>
            </link>
            <link>
                <url>/some/old/url</url>
            </link>
        </section>
        <section>
            <link>
                <url>
                    /a/different/old/url?with=specialChars&amp;escaped=true
                </url>
            </link>
        </section>
    </content>
</page>

Once the script has run, example.xml should contain:

<?xml version="1.0" encoding="UTF-8"?>
<page>
    <content>
        <section>
            <link>
                <url>/a/new/and/improved/url</url>
            </link>
            <link>
                <url>/a/new/and/improved/url</url>
            </link>
        </section>
        <section>
            <link>
                <url>
                    /a/different/new/and/improved/url?with=specialChars&amp;stillEscaped=true
                </url>
            </link>
        </section>
    </content>
</page>

This is easy to do using groovy's excellent xml support, except that I want to change the URLs and nothing else about the file.

By that I mean:

• whitespace must not change (files might contain spaces, tabs, or both)
• comments must be preserved
• windows vs. unix-style line separators must be preserved
• the xml declaration at the top must not be added or removed
• attributes in tags must retain their order

So far, after trying many combinations of XmlParser, DOMBuilder, XmlNodePrinter, XmlUtil.serialize(), and so on, I've landed on reading each file line-by-line and applying an ugly hybrid of the xml utilities and regular expressions.

Reading and writing each file:

files.each { File file ->
    def lineEnding = file.text.contains('\r\n') ? '\r\n' : '\n'
    def newLineAtEof = file.text.endsWith(lineEnding)
    def lines = file.readLines()
    file.withWriter { w ->
        lines.eachWithIndex { line, index ->
            line = update(line)
            w.write(line)
            if (index < lines.size-1) w.write(lineEnding)
            else if (newLineAtEof) w.write(lineEnding)
        }
    }
}

Searching for and updating URLs within a line:

def matcher = (line =~ urlTagRegexp) //matches a <url> element and its contents
matcher.each { groups ->
    def urlNode = new XmlParser().parseText(line)
    def url = urlNode.text()
    def newUrl = translate(url)
    if (newUrl) {
        urlNode.value = newUrl
        def replacement = nodeToString(urlNode)
        line = matcher.replaceAll(replacement)
    }
}

def nodeToString(node) {
    def writer = new StringWriter()
    writer.withPrintWriter { printWriter ->
        def printer = new XmlNodePrinter(printWriter)
        printer.preserveWhitespace = true
        printer.print(node)
    }
    writer.toString().replaceAll(/[\r\n]/, '')
}

This mostly works, except it can't handle a tag split over multiple lines, and messing with newlines when writing the files back out is cumbersome.

I'm new to groovy, but I feel like there must be a groovier way of doing this.