HBase MapReduce实例分析
问题导读：1.hbase的mapreduce与hadoop mapreduce的区别点在什么地方？
2.java.lang.NoClassDefFoundError: org/apache/hadoop/hbase/HTableDescriptor可能的解决方案是什么？
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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 " mapreduce学习指导及疑难解惑汇总" 这篇文章来建立基本概念。
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;
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);
}
}二、把java代码打成jar包
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。
三、运行程序
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）：然后再次执行
四、查看HBase表中的数据
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。
学习学习。。
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