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.
Current status
Currently the code base is basically functional, but only trivially tested. In some places, this code is a literal conversion of the C++ code and in others it has been converted to a more natural Java style. The plan is to leave the code closer to the C++ original until the baseline performance has been established.
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);
Projects using this port of LevelDB
- ActiveMQ Apollo: Defaults to using leveldbjni, but falls back to this port if the jni port is not available on your platform.
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