Trie (tr13) builder that uses a LevelDB instance to create a tr13 file to use for reading (note: mem usage linear to result size)

gistfile1.txt

import com.ning.tr13.KeyValueSource;
import com.ning.tr13.impl.bytes.BytesValueReader;
import com.ning.tr13.impl.bytes.SimpleBytesTrieBuilder;
import org.iq80.leveldb.CompressionType;
import org.iq80.leveldb.DB;
import org.iq80.leveldb.DBIterator;
import org.iq80.leveldb.Options;
import org.iq80.leveldb.impl.Iq80DBFactory;

import java.io.*;
import java.util.Map;

public class PrintNamesAsTrie
{
    public static void main(String[] args) throws Exception
    {
        if (args.length != 2) {
            System.err.println("Usage: java ... [leveldb-directory] [trie-output-file]");
            System.exit(1);
        }
        File dbDir = new File(args[0]).getCanonicalFile();
        File trieFile = new File(args[1]);

        Options options = new Options();
        options.createIfMissing(false);
        DB db = new Iq80DBFactory().open(dbDir, options);
        DBIterator iterator = db.iterator();

        MyInputHandler src = new MyInputHandler(iterator);

        SimpleBytesTrieBuilder b = new SimpleBytesTrieBuilder(src, true);
        File outputFile = new File(args[1]);
        OutputStream out = new FileOutputStream(outputFile);
        b.buildAndWrite(out, true);
        out.close();
        System.out.println("Build complete: "+src.getLineNumber()+" lines read, result file length is "+(outputFile.length()>>10)+" kB");

        db.close();
    }

    static class MyInputHandler extends KeyValueSource<byte[]>
    {
        protected final DBIterator iterator;

        protected int entries;

        public MyInputHandler(DBIterator it) {
            iterator = it;
        }

        public void readAll(ValueCallback<byte[]> handler) throws IOException {
            while (iterator.hasNext()) {
                ++entries;
                Map.Entry<byte[], byte[]> entry = iterator.next();
                // could strip out trailing zero, but leave in for now
                handler.handleEntry(entry.getKey(), entry.getValue());
            }
            iterator.close();
        }

        public int getLineNumber() {
            return entries;
        }
    }
}