What's the most standard Java way to store raw binary data along with XML?

Question

I need to store a huge amount of binary data into a file, but I want also to read/write the header of that file in XML format.

Yes, I could just store the binary

Answer 1

I followed the concept suggested by Blaise Doughan, but without attachment marshallers:

I let an XmlAdapter convert a byte[] to a URI-reference and back, while references point to separate files, where raw data is stored. The XML file and all binary files are then put into a zip.

It is similar to the approach of OpenOffice and the ODF format, which in fact is a zip with few XMLs and binary files.

(In the example code, no actual binary files are written, and no zip is created.)

Bindings.java

import java.net.*;
import java.util.*;
import javax.xml.bind.annotation.*;
import javax.xml.bind.annotation.adapters.*;

final class Bindings {

  static final String SCHEME = "storage";
  static final Class[] ALL_CLASSES = new Class[]{
    Root.class, RawRef.class
  };

  static final class RawRepository
      extends XmlAdapter {

    final SortedMap map = new TreeMap<>();
    final String host;
    private int lastID = 0;

    RawRepository(String host) {
      this.host = host;
    }

    @Override
    public byte[] unmarshal(URI o) {
      if (!SCHEME.equals(o.getScheme())) {
        throw new Error("scheme is: " + o.getScheme()
            + ", while expected was: " + SCHEME);
      } else if (!host.equals(o.getHost())) {
        throw new Error("host is: " + o.getHost()
            + ", while expected was: " + host);
      }

      String key = o.getPath();
      if (!map.containsKey(key)) {
        throw new Error("key not found: " + key);
      }

      byte[] ret = map.get(key);
      return Arrays.copyOf(ret, ret.length);
    }

    @Override
    public URI marshal(byte[] o) {
      ++lastID;
      String key = String.valueOf(lastID);
      map.put(key, Arrays.copyOf(o, o.length));

      try {
        return new URI(SCHEME, host, "/" + key, null);
      } catch (URISyntaxException ex) {
        throw new Error(ex);
      }
    }

  }

  @XmlRootElement
  @XmlType
  static final class Root {

    @XmlElement
    final List element = new LinkedList<>();
  }

  @XmlType
  static final class RawRef {

    @XmlJavaTypeAdapter(RawRepository.class)
    @XmlElement
    byte[] raw = null;
  }

}

Main.java

import java.io.*;
import javax.xml.bind.*;

public class _Run {

  public static void main(String[] args)
      throws Exception {
    JAXBContext context = JAXBContext.newInstance(Bindings.ALL_CLASSES);
    Marshaller marshaller = context.createMarshaller();
    marshaller.setProperty(Marshaller.JAXB_FORMATTED_OUTPUT, true);
    Unmarshaller unmarshaller = context.createUnmarshaller();

    Bindings.RawRepository adapter = new Bindings.RawRepository("myZipVFS");
    marshaller.setAdapter(adapter);

    Bindings.RawRef ta1 = new Bindings.RawRef();
    ta1.raw = "THIS IS A STRING".getBytes();
    Bindings.RawRef ta2 = new Bindings.RawRef();
    ta2.raw = "THIS IS AN OTHER STRING".getBytes();

    Bindings.Root root = new Bindings.Root();
    root.element.add(ta1);
    root.element.add(ta2);

    StringWriter out = new StringWriter();
    marshaller.marshal(root, out);

    System.out.println(out.toString());
  }

}

Output

    
        storage://myZipVFS/1
    
    
        storage://myZipVFS/2