[Java] Add a basic binding and test for BackupableDB and StackableDB.

Summary:
Add a skeleton binding and test for BackupableDB which shows that BackupableDB
and RocksDB can share the same JNI calls.

Test Plan:
make rocksdbjava
make jtest

Reviewers: haobo, ankgup87, sdong, dhruba

Reviewed By: haobo

CC: leveldb

Differential Revision: https://reviews.facebook.net/D17793

java/org/rocksdb/BackupableDB.java

@@ -0,0 +1,84 @@
+// Copyright (c) 2014, Facebook, Inc.  All rights reserved.
+// This source code is licensed under the BSD-style license found in the
+// LICENSE file in the root directory of this source tree. An additional grant
+// of patent rights can be found in the PATENTS file in the same directory.
+
+package org.rocksdb;
+
+/**
+ * A subclass of RocksDB which supports backup-related operations.
+ *
+ * @see BackupableDBOptions
+ */
+public class BackupableDB extends RocksDB {
+  /**
+   * Open a BackupableDB under the specified path.
+   * Note that the backup path should be set properly in the
+   * input BackupableDBOptions.
+   *
+   * @param opt options for db.
+   * @param bopt backup related options.
+   * @param the db path for storing data.  The path for storing
+   *     backup should be specified in the BackupableDBOptions.
+   * @return reference to the opened BackupableDB.
+   */
+  public static BackupableDB open(
+      Options opt, BackupableDBOptions bopt, String db_path)
+      throws RocksDBException {
+    // since BackupableDB c++ will handle the life cycle of
+    // the returned RocksDB of RocksDB.open(), here we store
+    // it as a BackupableDB member variable to avoid GC.
+    BackupableDB bdb = new BackupableDB(RocksDB.open(opt, db_path));
+    bdb.open(bdb.db_.nativeHandle_, bopt.nativeHandle_);
+
+    return bdb;
+  }
+
+  /**
+   * Captures the state of the database in the latest backup.
+   * Note that this function is not thread-safe.
+   *
+   * @param flushBeforeBackup if true, then all data will be flushed
+   *     before creating backup.
+   */
+  public void createNewBackup(boolean flushBeforeBackup) {
+    createNewBackup(nativeHandle_, flushBeforeBackup);
+  }
+
+
+  /**
+   * Close the BackupableDB instance and release resource.
+   *
+   * Internally, BackupableDB owns the rocksdb::DB pointer to its
+   * associated RocksDB.  The release of that RocksDB pointer is
+   * handled in the destructor of the c++ rocksdb::BackupableDB and
+   * should be transparent to Java developers.
+   */
+  @Override public synchronized void close() {
+    if (isOpened()) {
+      super.close0();
+    }
+  }
+
+  /**
+   * A protected construction that will be used in the static factory
+   * method BackupableDB.open().
+   */
+  protected BackupableDB(RocksDB db) {
+    super();
+    db_ = db;
+  }
+
+  @Override protected void finalize() {
+    close();
+  }
+
+  private boolean isOpened() {
+    return nativeHandle_ != 0;
+  }
+
+  protected native void open(long rocksDBHandle, long backupDBOptionsHandle);
+  protected native void createNewBackup(long handle, boolean flag);
+
+  private final RocksDB db_;
+}