B-Encode

This library allows you to encode and decode B-encoded documents.

Before:

Map<String,BEncodedValue> document = new HashMap<String, BEncodedValue>() {{
    put("string", new BEncodedValue("value"));
    put("number", new BEncodedValue(123456));
    put("list", new BEncodedValue(new ArrayList<BEncodedValue>() {{
        add(new BEncodedValue("list-item-1"));
        add(new BEncodedValue("list-item-2"));
    }}));
    put("dict", new BEncodedValue(new HashMap<String, BEncodedValue>() {{
        put("123", new BEncodedValue("test"));
        put("456", new BEncodedValue("thing"));
    }}));
}};

ByteArrayOutputStream baos = new ByteArrayOutputStream();
BEncoder.encode(document, baos);
String encodedDocument = new String(baos.toByteArray());

After:

d
	4:dict		d
					3:123	4:test
					3:456	5:thing
				e
	4:list		l
					11:list-item-1
					11:list-item-2
				e
	6:number	i123456e
	6:string	5:value
e

The library can do the reverse operation as well: decode.

I want to decode a torrent file. How can I do that?

First you need to read the torrent and decode it:

File torrentFile = "file.torrent";
FileInputStream inputStream = new FileInputStream(torrentFile);
BDecoder reader = new BDecoder(inputStream);
Map<String, BEncodedValue> document = reader.decodeMap().getMap();

Then you can start extracting information from it:

String announce = document.get("announce").getString(); // Strings
Map<String, BEncodedValue> info = document.get("info").getMap(); // Maps
List<BEncodedValue> files = info.get("files").getList(); // Lists

You can check if a key exists using the 'containsKey' method as such:

if (document.containsKey("info")) {
    System.out.println("The info field exists");
}

Use the library

The documentation page lists how you can add this library as a dependency of your project.

Credit

This library was created since no other viable libraries existed, and the ttorrent project contains a bunch of unecessary content. It is based on the work of Maxime Petazzoni.