（三）实战4：hbase的MapReduce之Java操作

编写 mapreduce 程序从 hbase 读取数据，然后存储到 hdfs

/**

• 描述：
  */
  public class HBaseDataToHDFSMR {
  public static final String ZK_CONNECT = “hadoop02:2181,hadoop03:2181,hadoop04:2181”;
  public static final String ZK_CONNECT_KEY = “hbase.zookeeper.quorum”;
  public static final String HDFS_CONNECT = “hdfs://myha01/”;
  public static final String HDFS_CONNECT_KEY = “fs.defaultFS”;
  public static void main(String[] args) throws Exception {
  Configuration conf = HBaseConfiguration.create();
  conf.set(ZK_CONNECT_KEY, ZK_CONNECT);
  conf.set(HDFS_CONNECT_KEY, HDFS_CONNECT);
  System.setProperty(“HADOOP_USER_NAME”, “hadoop”);
  Job job = Job.getInstance(conf);
  // 输入数据来源于 hbase 的 user_info 表
  Scan scan = new Scan();
  TableMapReduceUtil.initTableMapperJob(“user_info”, scan,
  Stay hungry Stay foolish --马中华-- http://blog.csdn.net/zhongqi2513
  HBaseDataToHDFSMRMapper.class, Text.class, NullWritable.class, job);
  // RecordReader — TableRecordReader
  // InputFormat ----- TextInputFormat
  // 数据输出到 hdfs
  FileOutputFormat.setOutputPath(job, new Path("/hbase2hdfs/output2"));
  boolean waitForCompletion = job.waitForCompletion(true);
  System.exit(waitForCompletion ? 0 : 1);
  }

static class HBaseDataToHDFSMRMapper extends TableMapper {
 /**
 * keyType: LongWritable -- ImmutableBytesWritable:rowkey
 * ValueType: Text -- Result:hbase 表中某一个 rowkey 查询出来的所有的 key-value 对
 */
 @Override
 protected void map(ImmutableBytesWritable key, Result value, Context context)
throws IOException, InterruptedException {
 // byte[] rowkey = Bytes.copy(key, 0, key.getLength());
 String rowkey = Bytes.toString(key.copyBytes());
 List listCells = value.listCells();
 Text text = new Text();
 // 最后输出格式是: rowkey, base_info:name-huangbo, base-info:age-34
 for (Cell cell : listCells) {
 String family = new String(CellUtil.cloneFamily(cell));
 String qualifier = new String(CellUtil.cloneQualifier(cell));
 String v = new String(CellUtil.cloneValue(cell));
 long ts = cell.getTimestamp();
 text.set(rowkey + "\t" + family + "\t" + qualifier + "\t" + v + "\t" + ts);
 context.write(text, NullWritable.get());
 }
 }
 }
}