Adds support for db->DefaultColumnFamily() to the Java API

java/org/rocksdb/RocksDB.java

@@ -1180,6 +1180,15 @@ public class RocksDB extends RocksObject {
     return iterators;
   }
 
+  /**
+   * Gets the handle for the default column family
+   *
+   * @return The handle of the default column family
+   */
+  public ColumnFamilyHandle getDefaultColumnFamily() {
+    return new ColumnFamilyHandle(this, getDefaultColumnFamily(nativeHandle_));
+  }
+
   /**
    * Creates a new column family with the name columnFamilyName and
    * allocates a ColumnFamilyHandle within an internal structure.
@@ -1620,6 +1629,7 @@ public class RocksDB extends RocksObject {
   protected native void releaseSnapshot(
       long nativeHandle, long snapshotHandle);
   private native void disposeInternal(long handle);
+  private native long getDefaultColumnFamily(long handle);
   private native long createColumnFamily(long handle,
       ColumnFamilyDescriptor columnFamilyDescriptor) throws RocksDBException;
   private native void dropColumnFamily(long handle, long cfHandle) throws RocksDBException;

java/org/rocksdb/test/ColumnFamilyTest.java

@@ -56,6 +56,40 @@ public class ColumnFamilyTest {
     }
   }
 
+  @Test
+  public void defaultColumnFamily() throws RocksDBException {
+    RocksDB db = null;
+    Options options = null;
+    try {
+      options = new Options();
+      options.setCreateIfMissing(true);
+
+      DBOptions dbOptions = new DBOptions();
+      dbOptions.setCreateIfMissing(true);
+
+      db = RocksDB.open(options, dbFolder.getRoot().getAbsolutePath());
+      ColumnFamilyHandle cfh = db.getDefaultColumnFamily();
+      assertThat(cfh).isNotNull();
+
+      final byte[] key = "key".getBytes();
+      final byte[] value = "value".getBytes();
+
+      db.put(cfh, key, value);
+
+      final byte[] actualValue = db.get(cfh, key);
+
+      assertThat(cfh).isNotNull();
+      assertThat(actualValue).isEqualTo(value);
+    } finally {
+      if (db != null) {
+        db.close();
+      }
+      if (options != null) {
+        options.dispose();
+      }
+    }
+  }
+
   @Test
   public void createColumnFamily() throws RocksDBException {
     RocksDB db = null;

java/rocksjni/rocksjni.cc

@@ -1174,6 +1174,18 @@ jlongArray Java_org_rocksdb_RocksDB_iterators(
   return env->NewLongArray(0);
 }
 
+/*
+ * Class:     org_rocksdb_RocksDB
+ * Method:    getDefaultColumnFamily
+ * Signature: (J)J
+ */
+jlong Java_org_rocksdb_RocksDB_getDefaultColumnFamily(
+    JNIEnv* env, jobject jobj, jlong jdb_handle) {
+  auto* db_handle = reinterpret_cast<rocksdb::DB*>(jdb_handle);
+  auto* cf_handle = db_handle->DefaultColumnFamily();
+  return reinterpret_cast<jlong>(cf_handle);
+}
+
 /*
  * Class:     org_rocksdb_RocksDB
  * Method:    createColumnFamily