1 /* 2 * Copyright 2010 The Apache Software Foundation 3 * 4 * Licensed to the Apache Software Foundation (ASF) under one 5 * or more contributor license agreements. See the NOTICE file 6 * distributed with this work for additional information 7 * regarding copyright ownership. The ASF licenses this file 8 * to you under the Apache License, Version 2.0 (the 9 * "License"); you may not use this file except in compliance 10 * with the License. You may obtain a copy of the License at 11 * 12 * http://www.apache.org/licenses/LICENSE-2.0 13 * 14 * Unless required by applicable law or agreed to in writing, software 15 * distributed under the License is distributed on an "AS IS" BASIS, 16 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 17 * See the License for the specific language governing permissions and 18 * limitations under the License. 19 */ 20 package org.apache.hadoop.hbase.filter; 21 22 import org.apache.hadoop.hbase.KeyValue; 23 24 import java.io.DataOutput; 25 import java.io.IOException; 26 import java.io.DataInput; 27 import java.util.List; 28 29 /** 30 * A filter that will only return the first KV from each row. 31 * <p> 32 * This filter can be used to more efficiently perform row count operations. 33 */ 34 public class FirstKeyOnlyFilter extends FilterBase { 35 private boolean foundKV = false; 36 37 public FirstKeyOnlyFilter() { 38 } 39 40 public void reset() { 41 foundKV = false; 42 } 43 44 public ReturnCode filterKeyValue(KeyValue v) { 45 if(foundKV) return ReturnCode.NEXT_ROW; 46 foundKV = true; 47 return ReturnCode.INCLUDE; 48 } 49 50 public void write(DataOutput out) throws IOException { 51 } 52 53 public void readFields(DataInput in) throws IOException { 54 } 55 }