Read bson files to documents in Java/Groovy

readBson.groovy

/**
 * Publishing this publicly because it took me so long to get to this stage:
 * - Using a memory-mapped byte buffer because I will handle *large* files.
 * - Not too happy with the end of my loop, but I could not find how to check for the end of the buffer otherwise.
 */
import org.bson.BsonBinaryReader
import org.bson.BsonReader
import org.bson.Document
import org.bson.codecs.DecoderContext
import org.bson.codecs.DocumentCodec

import java.nio.BufferUnderflowException
import java.nio.MappedByteBuffer
import java.nio.channels.FileChannel

RandomAccessFile aFile = new RandomAccessFile("./assets.bson", "r");
FileChannel inChannel = aFile.getChannel();
MappedByteBuffer buffer = inChannel.map(FileChannel.MapMode.READ_ONLY, 0, inChannel.size());
buffer.load();

while (true) {
    BsonReader reader = new BsonBinaryReader(buffer)

    DecoderContext decoderContext = DecoderContext.builder().build()
    DocumentCodec codec = new DocumentCodec()
    try {
        Document document = codec.decode(reader, decoderContext)
        println document.get('_id')
    } catch (BufferUnderflowException e) {
        println "DONE"
        break;
    }
}