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）：
[java]
/**
* 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 {
    <span style="color:#ff0000;">static final Log LOG = LogFactory.getLog(RowPaginationFilter.class);
</span> 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;
    }

    @Override
    public void reset() {
        // noop
    }
    @Override
    public boolean filterAllRemaining() {
        return this.rowsAccepted > this.limit+this.offset;
    }
    @Override
    public boolean filterRowKey(byte[] rowKey, int offset, int length) {
        return false;
    }
    @Override
    public void readFields(final DataInput in) throws IOException {
        this.offset = in.readInt();
        this.limit = in.readInt();
    }
    @Override
    public void write(final DataOutput out) throws IOException {
        out.writeInt(offset);
        out.writeInt(limit);
    }
    @Override
    public ReturnCode filterKeyValue(KeyValue v) {
        return ReturnCode.INCLUDE;
    }
    //true to exclude row, false to include row.
    @Override
    public boolean filterRow() {
        boolean isExclude = this.rowsAccepted < this.offset || this.rowsAccepted>=this.limit+this.offset;
        rowsAccepted++;
        return isExclude;
    }
}

补充：综合编程 , 其他综合 ,