LevelDB in Java

This is a rewrite (port) of LevelDB in Java. This goal is to have a feature complete implementation that is within 10% of the performance of the C++ original and produces byte-for-byte exact copies of the C++ code.

Purpose of this fork (leveldb-moj)

The code was adapted to be able to open Minecraft Android (MCPE) worlds. Changes:

• replaced sst extension with ldb
• added support for ZLIB and raw ZLIB compression

Althrough the library is able to read Minecraft worlds, there is no guarantee that changing them is safe, or even that simply reading them is safe. Please run the code on a copy of your Minecraft world in order to not corrupt the save.

API Usage:

Recommended Package imports:

import org.iq80.leveldb.*;
import static org.iq80.leveldb.impl.Iq80DBFactory.*;
import java.io.*;

Opening and closing the database.

Options options = new Options();
options.createIfMissing(true);
DB db = factory.open(new File("example"), options);
try {
  // Use the db in here....
} finally {
  // Make sure you close the db to shutdown the 
  // database and avoid resource leaks.
  db.close();
}

Putting, Getting, and Deleting key/values.

db.put(bytes("Tampa"), bytes("rocks"));
String value = asString(db.get(bytes("Tampa")));
db.delete(bytes("Tampa"), wo);

Performing Batch/Bulk/Atomic Updates.

WriteBatch batch = db.createWriteBatch();
try {
  batch.delete(bytes("Denver"));
  batch.put(bytes("Tampa"), bytes("green"));
  batch.put(bytes("London"), bytes("red"));

  db.write(batch);
} finally {
  // Make sure you close the batch to avoid resource leaks.
  batch.close();
}

Iterating key/values.

DBIterator iterator = db.iterator();
try {
  for(iterator.seekToFirst(); iterator.hasNext(); iterator.next()) {
    String key = asString(iterator.peekNext().getKey());
    String value = asString(iterator.peekNext().getValue());
    System.out.println(key+" = "+value);
  }
} finally {
  // Make sure you close the iterator to avoid resource leaks.
  iterator.close();
}

Working against a Snapshot view of the Database.

ReadOptions ro = new ReadOptions();
ro.snapshot(db.getSnapshot());
try {
  
  // All read operations will now use the same 
  // consistent view of the data.
  ... = db.iterator(ro);
  ... = db.get(bytes("Tampa"), ro);

} finally {
  // Make sure you close the snapshot to avoid resource leaks.
  ro.snapshot().close();
}

Using a custom Comparator.

DBComparator comparator = new DBComparator(){
    public int compare(byte[] key1, byte[] key2) {
        return new String(key1).compareTo(new String(key2));
    }
    public String name() {
        return "simple";
    }
    public byte[] findShortestSeparator(byte[] start, byte[] limit) {
        return start;
    }
    public byte[] findShortSuccessor(byte[] key) {
        return key;
    }
};
Options options = new Options();
options.comparator(comparator);
DB db = factory.open(new File("example"), options);

Disabling Compression

Options options = new Options();
options.compressionType(CompressionType.NONE);
DB db = factory.open(new File("example"), options);

Configuring the Cache

Options options = new Options();
options.cacheSize(100 * 1048576); // 100MB cache
DB db = factory.open(new File("example"), options);

Getting approximate sizes.

long[] sizes = db.getApproximateSizes(new Range(bytes("a"), bytes("k")), new Range(bytes("k"), bytes("z")));
System.out.println("Size: "+sizes[0]+", "+sizes[1]);

Getting database status.

String stats = db.getProperty("leveldb.stats");
System.out.println(stats);

Getting informational log messages.

Logger logger = new Logger() {
  public void log(String message) {
    System.out.println(message);
  }
};
Options options = new Options();
options.logger(logger);
DB db = factory.open(new File("example"), options);

Destroying a database.

Options options = new Options();
factory.destroy(new File("example"), options);