将原始二进制数据与 XML 一起存储的最标准 Java 方式是什么?

2022-01-19 00:00:00 xml serialization java jaxb xml-serialization

我需要将大量二进制数据存储到一个文件中，但我还想以 XML 格式读取/写入该文件的标题.

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.

是的，我可以将二进制数据存储到某个 XML 值中，然后使用 base64 编码对其进行序列化.但这不会节省空间.

我能否以或多或少标准化的方式混合"XML 数据和原始二进制数据?

Can I "mix" XML data and raw binary data in a more-or-less standardized way?

我在考虑两个选择:

  • 有没有办法使用 JAXB 做到这一点?

  • Is there a way to do this using JAXB?

或者有没有办法获取一些现有的 XML 数据并将二进制数据附加到它，以识别边界?

Or is there a way to take some existing XML data and append binary data to it, in such a way that the the boundary is recognized?

我正在寻找的概念不是被/用于 SOAP 吗?

Isn't the concept I'm looking for somehow used by / for SOAP?

还是在电子邮件标准中使用?(二进制附件的分离)

Or is it used in the email standard? (Separation of binary attachments)

我想要实现的方案:

[meta-info-about-boundary][XML-data][boundary][raw-binary-data]

谢谢！

推荐答案

我遵循了 Blaise Doughan 提出的概念，但没有附件 marshallers:

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

我让 XmlAdapter 将 byte[] 转换为 URI 引用并返回，而引用指向单独的文件，其中原始数据被存储.然后将 XML 文件和所有二进制文件放入一个 zip 文件中.

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.

类似于OpenOffice的做法和ODF格式，实际上是一个带有少量XML和二进制文件的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.

(在示例代码中，没有写入实际的二进制文件，也没有创建 zip.)

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<URI, byte[]> {

    final SortedMap<String, byte[]> 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<RawRef> 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());
  }

}

输出

<root>
    <element>
        <raw>storage://myZipVFS/1</raw>
    </element>
    <element>
        <raw>storage://myZipVFS/2</raw>
    </element>
</root>

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