Using regexp in java to modify an xml

Question

I'm trying to change an xml by using regular expressions in java, but I can't find the right way. I have an xml like this (simplified):

<ROOT>
   <NODE ord="1" />
   <NODE ord="3,2" />
</ROOT>

The xml actually shows a sentence with its nodes, chunks ... in two languages and has more attributes. Each sentence it's loaded in two RichTextAreas (one for the source sentence, and the other for the translated one).

What I need to do is add a style attribute to every node that has an specific value in its ord attribute (this style attribute will show correspondences between two languages, like Google Translate does when you mouse over a word). I know this could be done using DOM (getting all the NODE nodes and then seeing the ord attribute one by one), but I am looking for the fastest way to do the change as it is going to execute in the client side of my GWT app.

When that ord attribute has a single value (like in the first node) it is easy to do just taking the xml as a string and using the replaceAll() function . The problem is when the attribute has composed values (like in the second node).

For example, how could I do to add that attribute if the value I'm looking for is 2? I believe this could be done using regular expressions, but I can't find out how. Any hint or help would be appreciated (even if it doesn't use regexp and replaceAll function).

Thanks in advance.

Thou shalt never parse XML with regex. If you have problems getting your regex right, doubly so. — Tomalak
– Tomalak, Commented Mar 6, 2012 at 17:31
@Tomalak is 100% correct. Attempting to use a regex here is The Wrong Thing To Do. — Brian Roach
– Brian Roach, Commented Mar 6, 2012 at 17:35
I know it's not the rightest thing to do, but this will have to be done every time the user clicks a word and I thought parsing it everytime this happens wouldn't be very effective — Ion
– Ion, Commented Mar 6, 2012 at 18:56
That would remain to be seen. DOM processing is pretty fast and the average modern client has lots of CPU cycles to burn. Give it a try before you disregard it. — Tomalak
– Tomalak, Commented Mar 6, 2012 at 19:32

Tomalak · Accepted Answer · 2012-03-06 18:14:07Z

1

XPath can do this for you. You could select:

/ROOT/NODE[contains(concat(',', @ord, ','), ',2,')]

Since you intend to use GWT on the client, you could give gwtxslt a try. With it you could specify an XSLT stylesheet to do the transformation (i.e. adding the attribute) for you:

XsltProcessor processor = new XsltProcessor();
processor.importStyleSheet(styleSheetText);
processor.importSource(sourceText);
processor.setParameter("ord", "2");
processor.setParameter("style", "whatever");
String resultString = processor.transform();
// do something with resultString

where styleSheetText could be an XSLT document along the lines of

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:param name="ord"   select="''" />
  <xsl:param name="style" select="''" />

  <xsl:template match="node()|@*">
    <xsl:copy>
      <xsl:apply-templates select="node()|@*" />
    </xsl:copy>
  </xsl:template>

  <xsl:template match="NODE">
    <xsl:copy>
      <xsl:apply-templates select="@*" />
      <xsl:if test="contains(concat(',', @ord, ','), concat(',', $ord, ','))">
        <xsl:attribute name="style">
          <xsl:value-of select="$style" />
        </xsl:attribute>
      </xsl:if>
      <xsl:apply-templates select="node()" />
    </xsl:copy>
  </xsl:template>
</xsl:stylesheet>

Note that I use concat() to prevent partial matches in the comma-separated list that the attribute value of @ord actually is.

answered Mar 6, 2012 at 18:14

Tomalak

339k68 gold badges547 silver badges635 bronze badges

Sign up to request clarification or add additional context in comments.

5 Comments

Ion Over a year ago

Is it possible to add an attribute just using xpath? I am using totoe in client side.

Tomalak Over a year ago

@ion No. XPath is a pure query language, all it can do is select the right nodes. You must process the nodes one way or the other. XSLT is one of the ways to do it. A DOM would be another way.

Tomalak Over a year ago

In a way, Xpath is like regex. Regex can only select bits of text. To modify them, you need a programming language that hosts regex and can modify strings. Here you need an environment that hosts XPath and can modify XML documents.

Ion Over a year ago

That's what I thougth. I will give DOM a try then. By the way, you think I should use DOM approach as well for removing the style attributes (when a new word is clicked, every style attribute set before has to be removed)?

Tomalak Over a year ago

@ion Definitely. It's not at all a difficult operation. All complex website manipulation on the client works this way (i.e. web apps) and if not done horribly wrong it is amazingly fast. XPath was merely a suggestion to grab the right nodes, whether you use the DOM directly to actually process them or outsource the DOM work to XSLT is your decision.

Tim Pietzcker · Accepted Answer · 2012-03-06 17:34:27Z

1

String resultString = subjectString.replaceAll("<NODE ord=\"([^\"]*\\b2\\b[^\"]*)\" />", "<NODE ord=\"$1\" style=\"whatever\"/>");

will find any <NODE> tag that has a single ord attribute with a value of "2" (or "1,2" or "2,3" or "1,2,3" but not "12") and adds a style attribute.

This is quick and dirty, and rightfully advised against by many here, but for a one-off quick job it should be OK.

Explanation:

<NODE ord="  # Match <NODE ord:" verbatim
(            # Match and capture...
 [^"]*       #  any number of characters except "
 \b2\b       #  "2" as a whole word (surrounded by non-alphanumerics)
 [^"]*       #  any number of characters except "
)            # End of capturing group
" />         # Match " /> verbatim

answered Mar 6, 2012 at 17:34

Tim Pietzcker

337k59 gold badges520 silver badges572 bronze badges

2 Comments

Tim Pietzcker Over a year ago

@Ion: What didn't work exactly? More details, please. The problem with regexes is that they are very unforgiving - you've got to precisely define the rules. Case, whitespace, everything is significant.

Tim Pietzcker Over a year ago

...which also is an indicator why a parser nearly always is the better idea to handle XML because it will transparently handle all this for you. (Of course, the parser itself uses regexes to do this, exactly so you don't have to)

Michael Kay · Accepted Answer · 2012-03-06 18:38:35Z

1

I'm trying to change an xml by using regular expressions in java, but I can't find the right way.

That's because there isn't a right way. Regular expressions are not the right way to manipulate XML. That's because XML is not a regular grammar (which is a technical term in computer science, not a generalized insult.)

answered Mar 6, 2012 at 18:38

Michael Kay

165k11 gold badges97 silver badges173 bronze badges

1 Comment

Ion Over a year ago

I know that it's better to work with the xml as an xml, rather than as a simple string, but I just thougth the dom approach would be very expensive.

Adam · Accepted Answer · 2012-03-06 17:54:15Z

0

It might sound like overkill, but I'd consider using the standard DOM parsers to read the fragment, modify it using setAttribute() calls, and then write it out again. I know you said that efficiency is important, but how long does this really take? Testing shows 60ms on my ageing 2GHz pentium.

This approach will be more robust against comments, things split across lines etc. It is also much more likely to give you well-formed XML. Also things like your requirement of only doing it if certain values are present will become trivial.

public class AddStyleExample {

    public static void main(final String[] args) {
        String input = "<ROOT> <NODE ord=\"1\" /> <NODE ord=\"3,2\" /> </ROOT>";
        try {
            final DocumentBuilderFactory factory = DocumentBuilderFactory
                    .newInstance();
            factory.setValidating(false);
            factory.setNamespaceAware(false);
            DocumentBuilder builder;

            builder = factory.newDocumentBuilder();

            final Document doc = builder.parse(new InputSource(
                    new StringReader(input)));

            NodeList tags = doc.getElementsByTagName("NODE");
            for (int i = 0; i < tags.getLength(); i++) {
                Element node = (Element) tags.item(i);
                node.setAttribute("style", "example value");
            }
            StringWriter writer = new StringWriter();
            final StreamResult result = new StreamResult(writer);
            final Transformer t = TransformerFactory.newInstance()
                    .newTransformer();
            t.setOutputProperty(OutputKeys.INDENT, "yes");
            t.setOutputProperty(OutputKeys.OMIT_XML_DECLARATION, "yes");
            t.transform(new DOMSource(doc), result);
            System.out.println(writer.toString());

        } catch (ParserConfigurationException e) {
            e.printStackTrace();
        } catch (TransformerException e) {
            e.printStackTrace();
        } catch (SAXException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
}

edited Mar 6, 2012 at 17:54

answered Mar 6, 2012 at 17:29

Adam

36.9k9 gold badges104 silver badges145 bronze badges

2 Comments

Adam Over a year ago

OK accepted, but you did state you wanted to do regex rather than DOM parsing because of speed, not because it is not supported.

Ion Over a year ago

I use a kind of DOM approach in the RichTextArea where the mouse is clicked (I use the gwt-selection library to get the word clicked and add to it the attribute by getting its parent node). You thin I should use the DOM approach in the other RichTextArea (in the one where correspondences are going to be shown)? I know that would be the best way of doing it, as the well formedness of the xml won't be at risk.

Collectives™ on Stack Overflow

Using regexp in java to modify an xml

4 Answers 4

5 Comments

2 Comments

1 Comment

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

5 Comments

2 Comments

1 Comment

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related