HBase MapReduce实例分析之三

心已赠人 2022-11-09 11:25 156阅读 0赞

跟Hadoop的无缝集成使得使用MapReduce对HBase的数据进行分布式计算非常方便，本文将介绍HBase下 MapReduce开发要点。很好理解本文前提是你对Hadoop MapReduce有一定的了解，如果你是初次接触Hadoop MapReduce编程，可以参考 ["第一个MapReduce应用"][MapReduce] 这篇文章来建立基本概念。

一、Java代码

![复制代码][copycode.gif]

package hbase;
    
    import java.io.IOException;
    
    import org.apache.hadoop.conf.Configuration;
    import org.apache.hadoop.fs.Path;
    import org.apache.hadoop.hbase.HBaseConfiguration;
    import org.apache.hadoop.hbase.HColumnDescriptor;
    import org.apache.hadoop.hbase.HTableDescriptor;
    import org.apache.hadoop.hbase.client.HBaseAdmin;
    import org.apache.hadoop.hbase.client.Put;
    import org.apache.hadoop.hbase.mapreduce.TableOutputFormat;
    import org.apache.hadoop.hbase.mapreduce.TableReducer;
    import org.apache.hadoop.hbase.util.Bytes;
    import org.apache.hadoop.io.IntWritable;
    import org.apache.hadoop.io.LongWritable;
    import org.apache.hadoop.io.NullWritable;
    import org.apache.hadoop.io.Text;
    import org.apache.hadoop.mapreduce.Job;
    import org.apache.hadoop.mapreduce.Mapper;
    import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
    import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
    
    public class WordCountHBase {
    
        public static class Map extends
                Mapper<LongWritable, Text, Text, IntWritable> {
            private IntWritable i = new IntWritable(1);
    
            public void map(LongWritable key, Text value, Context context)
                    throws IOException, InterruptedException {
                String s[] = value.toString().trim().split(" ");
                // 将输入的每行以空格分开
                for (String m : s) {
                    context.write(new Text(m), i);
                }
            }
        }
    
        public static class Reduce extends
                TableReducer<Text, IntWritable, NullWritable> {
            public void reduce(Text key, Iterable<IntWritable> values,
                    Context context) throws IOException, InterruptedException {
                int sum = 0;
                for (IntWritable i : values) {
                    sum += i.get();
                }
                Put put = new Put(Bytes.toBytes(key.toString()));
                // Put实例化，每一个词存一行
                put.add(Bytes.toBytes("content"), Bytes.toBytes("count"),
                        Bytes.toBytes(String.valueOf(sum)));
                // 列族为content，列为count，列值为数目
                context.write(NullWritable.get(), put);
            }
        }
    
        public static void createHBaseTable(String tableName) throws IOException {
            HTableDescriptor htd = new HTableDescriptor(tableName);
            HColumnDescriptor col = new HColumnDescriptor("content");
            htd.addFamily(col);
            Configuration conf = HBaseConfiguration.create();
            conf.set("hbase.zookeeper.quorum", "libin2");
            HBaseAdmin admin = new HBaseAdmin(conf);
            if (admin.tableExists(tableName)) {
                System.out.println("table exists, trying to recreate table......");
                admin.disableTable(tableName);
                admin.deleteTable(tableName);
            }
            System.out.println("create new table:" + tableName);
            admin.createTable(htd);
        }
    
        public static void main(String[] args) throws IOException,
                InterruptedException, ClassNotFoundException {
            String tableName = "WordCount";
            Configuration conf = new Configuration();
            conf.set(TableOutputFormat.OUTPUT_TABLE, tableName);
            createHBaseTable(tableName);
            String input = args[0];
            Job job = new Job(conf, "WordCount table with " + input);
            job.setJarByClass(WordCountHBase.class);
            job.setNumReduceTasks(3);
            job.setMapperClass(Map.class);
            job.setReducerClass(Reduce.class);
            job.setMapOutputKeyClass(Text.class);
            job.setMapOutputValueClass(IntWritable.class);
            job.setInputFormatClass(TextInputFormat.class);
            job.setOutputFormatClass(TableOutputFormat.class);
            FileInputFormat.addInputPath(job, new Path(input));
            System.exit(job.waitForCompletion(true) ? 0 : 1);
        }
    }

![复制代码][copycode.gif]

二、把java代码打成jar包

![Image 1][]

如果同时用到了两个jar包，需要在两个jar包之间加一个":"分隔符。

![Image 1][]

三、运行程序

![Image 1][]

运行WordCountHBase.jar可能会报错：java.lang.NoClassDefFoundError: org/apache/hadoop/hbase/HTableDescriptor

解决方法（把hbase的核心jar包和hbase自带的Zookeeperjar包拷贝到hadoop的安装目录\\lib下，然后重启服务）：![Image 1][]

然后再次执行

![Image 1][]

四、查看HBase表中的数据

![Image 1][]

如果表中有保存好的MapReduce处理后的数据，说明成功！本文通过实例分析演示了使用MapReduce分析HBase的数据，需要注意的这只是一种常规的方式（分析表中的数据存到另外的表中），实际上不局限于此，不过其他方式跟此类似。

[MapReduce]: http://www.cnblogs.com/NicholasLee/archive/2012/08/28/2660046.html
[copycode.gif]: /images/20221023/2e7ebda00ec746bc8af640e664a91899.png
[Image 1]: