如何在java中执行replaceAll排除注释

Question

I have a file, typically XML files. I want to replace all the occurrences of 'xy' with 'p.q'. But during this replacement, i want to ignore the occurrences of xy in comments ().

I was trying to use String.replaceAll() to perform this task.

For Example :

<?xml version="1.0" encoding="UTF-8"?>
<name>This occurrence of x.y should be replaced</name>
<!-- This occurrence of x.y should not be replaced -->

I tried using String.replaceAll("x[\\.]y", "pq") but i could see that occurrences in comments are also getting replaced

I could use an other alternative by which i can read the file line by line and exclude the lines that starts with comments, but i am interested in using replaceAll()

Please provide a way by which this can be achieved.

Answer 1

Although this isn't strictly the answer you are looking for, I have a recommendation.

I'd recommend using a proper XML parser like Java DOM to check and replace text in your nodes, rather than dealing with your XML as a raw String . Something like this should replace the corresponding text in your node if they are not a comment.

File f = new File("your.xml");
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(f);

NodeList eList = doc.getElementsByTagName("*");
for (int e = 0; e < eList.getLength(); e++) {
    Node element = eList.item(e);
    NodeList nList = element.getChildNodes();
    for(int n = 0; n < nList.getLength(); n++){
        Node node = nList.item(n);
        if(node.getNodeType()==Node.TEXT_NODE){
            node.setNodeValue(node.getNodeValue().replace("x.y", "p.q")); 
        }
    }
}

If memory/efficiency are an issue (like when your.xml is huge), you would be better off using SAX , which is faster (a little more code intensive) and doesn't store the XML in memory.

Once your Document has been edited you'll probably want to use a Transformer to create a suitable output. ( Official guide here , curtsey of Boris the Spider's comment)

Hope this helps.

Further Reading;

• Official Java DOM tutorials
• Parsing HTML the Cthulhu way (why parsing XML/HTML with regex is bad)
• Why is it such a bad idea to parse XML with regex?
• Using regular expressions to parse HTML: why not?
• Comical Answer about parsing [X]HTML with regex

Answer 2

If using regex, an option would be to use lookarounds for checking to replace only outside comments:

(?s)x\.y(?!(?:(?!<!--).)+-->)

As a Java string:

"(?s)x\\.y(?!(?:(?!<!--).)+-->)"

Used the (?s) DOTALL modifier for making the . also match newlines.

Test at regexplanet (click on Java )