自写filter步骤和注意事项
hbase本身提供了很多filter来实现服务器端过滤的功能，诸如
Filter, FilterBase, CompareFilter;
一些Comparators类;
Comparison Filters;
Dedicated Filters;
Decorating Filters;
FilterList;
Custom Filters。
但是这些filter往往不能满足我们的实际需要，因此我们可以针对自己需要来自写filter，然后加到hbase集群中。
主要步骤：
1.新建类，继承自FilterBase或WritableByteArrayComparable，需求不同，需要创建的类不同，不详述
2.将相关类打成jar包
3.将jar包copy到hbase集群中各机器的 $HBASE_HOME/lib 目录下，并重启集群
4.在客户端开发时，添加此jar包到路经
OK，可以使用了。
注意事项：
1.新建类中，需要添加常量 LOG. 否则出现
can't seal package org.apache.hadoop.hbase.filter: already loaded
异常提示
2.必须将jar包copy到hbase集群中各机器的 $HBASE_HOME/lib 目录下，并重启hbase集群
参考代码
如下（网友写的，帮忙解决了点问题）：
/** * Copyright 2008 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.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.apache.hadoop.hbase.KeyValue;import org.apache.hadoop.hbase.filter.FilterBase;/** * A filter, based on the PageFilter, takes two arguments: limit and offset. * This filter can be used for specified row count, in order to efficient * lookups and paginated results for end users. * */public class RowPaginationFilter extends FilterBase {static final Log LOG = LogFactory.getLog(RowPaginationFilter.class);private int rowsAccepted = 0;private int limit = 0;private int offset = 0;/** * Default constructor, filters nothing. Required though for RPC * deserialization. */public RowPaginationFilter() {}/** * Constructor that takes a maximum page size. * * get row from offset to offset+limit ( offset<= row<=offset+limit ) * @param offset start position * @param limit count from offset position */public RowPaginationFilter(final int offset, final int limit) {this.offset = offset;this.limit = limit;}@Overridepublic void reset() {// noop}@Overridepublic boolean filterAllRemaining() {return this.rowsAccepted > this.limit+this.offset;}@Overridepublic boolean filterRowKey(byte[] rowKey, int offset, int length) {return false;}@Overridepublic void readFields(final DataInput in) throws IOException {this.offset = in.readInt();this.limit = in.readInt();}@Overridepublic void write(final DataOutput out) throws IOException {out.writeInt(offset);out.writeInt(limit);}@Overridepublic ReturnCode filterKeyValue(KeyValue v) {return ReturnCode.INCLUDE;}//true to exclude row, false to include row.@Overridepublic boolean filterRow() {boolean isExclude = this.rowsAccepted < this.offset || this.rowsAccepted>=this.limit+this.offset;rowsAccepted++;return isExclude;}}