HBASE-3211 second commit, missed KeyOnlyFilter.java

git-svn-id: https://svn.apache.org/repos/asf/hbase/trunk@1033780 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/hadoop/hbase/filter/KeyOnlyFilter.java

@@ -0,0 +1,47 @@
+/*
+ * Copyright 2010 The Apache Software Foundation
+ *
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.filter;
+
+import java.io.DataInput;
+import java.io.DataOutput;
+import java.io.IOException;
+import org.apache.hadoop.hbase.KeyValue;
+
+/**
+ * A filter that will only return the key component of each KV (the value will
+ * be rewritten as empty).
+ * <p>
+ * This filter can be used to grab all of the keys without having to also grab
+ * the values.
+ */
+public class KeyOnlyFilter extends FilterBase {
+
+  public KeyOnlyFilter() {}
+
+  @Override
+  public ReturnCode filterKeyValue(KeyValue kv) {
+    kv.convertToKeyOnly();
+    return ReturnCode.INCLUDE;
+  }
+
+  public void write(DataOutput out) throws IOException {}
+
+  public void readFields(DataInput in) throws IOException {}
+}