How to access file name within a DoFn in an unbounded pipeline

Question

I'm looking for a way to access the name of the file being processed during the data transformation within a DoFn.

My pipeline is as shown below:

Pipeline p = Pipeline.create(options);

p.apply(FileIO.match()
                .filepattern(options.getInput())
                    .continuously(Duration.standardSeconds(5), 
                            Watch.Growth.<String>never()))
.apply(FileIO.readMatches()
            .withCompression(Compression.GZIP))
.apply(XmlIO.<MyString>readFiles()
            .withRootElement("root")
                .withRecordElement("record")
                    .withRecordClass(MyString.class))//<-- This only returns the contents of the file
.apply(ParDo.of(new ProcessRecord()))//<-- I need to access file name here
.apply(ParDo.of(new FormatRecord()))
.apply(Window.<String>into(FixedWindows.of(Duration.standardSeconds(5))))
.apply(new CustomWrite(options));

Each file that is processed is an XML document. While processing the content, I need access to the name of the file being processed too to include in the transformed record.

Is there a way to achieve this?

This post has a similar question, but since i'm trying to use XmlIO I havent found a way to access the file metadata.

Below is the approach I found online, but not sure if there is a way to use it in the pipeline described above.

p.apply(FileIO.match()
                .filepattern(options.getInput())
                    .continuously(Duration.standardSeconds(5), 
                            Watch.Growth.<String>never()))//File Metadata
.apply(FileIO.readMatches()
            .withCompression(Compression.GZIP))//Readable Files
.apply(MapElements
            .into(TypeDescriptors.kvs(TypeDescriptors.strings(),new TypeDescriptor<ReadableFile>() {} ))
            .via((ReadableFile file) -> {
                return KV.of(file.getMetadata().resourceId().getFilename(),file);
            })
 );         

Any suggestions are highly appreciated. Thank you for your time reviewing this.

EDIT:

I took Alexey's advice and implemented a custom XmlIO. It would be nice if we could just extend the class we need and override the appropriate method. However, in this specific case, there was a reference to one method which was protected within the sdk because of which I couldn't easily override what i needed and instead ended up copying a whole bunch of files. While this works for now, I hope in future there is a more straighforward way to access the file metadata in these IO implementations.