如何检查XML文件中的更改？

Question

I want to make sure 2 XML files are the same, and the 2 options I see are. 1. Get the XML to have a last modification date with time, and check that is the same. Problem is that someone may forget to change it and then it is useless. 2. Create a hashcode of the xml file/structure.

I use a build in library in java, but the hash implementation can change from run to run which is not helpful

File model = new File(fileLocation);
DocumentBuilderFactory dbFactory = DocumentBuilderFactory.newInstance();
DocumentBuilder dBuilder = dbFactory.newDocumentBuilder();
Document doc = dBuilder.parse(model);
doc.getHash();

is there an easy way to do this, and hopefully without importing another library.

Answer 1

Will sorting the file and comparing help?

In case of libraries, You can try diffxml .

XMLUnit has a diff feature

Answer 2

As Martin Thurau pointed out, it depends, whether you want to check if the files are identical, or if the XML content is identical. This answer is only for the first case, when you want to know if two files are identical, i think that was your question because you suggested a hash value.

In this case building a hash is not a good choice, you can solve it easier like this:

1. Check whether the file sizes are the same, if not they are not identical.
2. Open a stream of both files.
3. Just loop through the streams and stop by the first difference.
4. If no differences where found, they are identical.

So why not calculating a hash value? You have to read the whole file anyway to calculate a hash, so when you compare the streams you can forgo the calculation, and you can stop by the first difference. Parsing the file to a DOM model will also have the same disadvantages.