HBase 扫描(scan)

使用HBase Shell扫描

scan命令用于在HTable查看数据。使用scan命令，可以获得表数据。其语法如下：


scan '<table name>'

例 - 以下示例显示如何使用scan命令从表中读取数据。在这里，我们正在阅读emp表。


hbase(main):010:0> scan 'emp'

ROW                           COLUMN + CELL

1 column = personal data:city, timestamp = 1417521848375, value = hyderabad
 
1 column = personal data:name, timestamp = 1417521785385, value = ramu

1 column = professional data:designation, timestamp = 1417585277,value = manager

1 column = professional data:salary, timestamp = 1417521903862, value = 50000

1 row(s) in 0.0370 seconds

使用Java API扫描

使用Java API扫描整个表数据的完整程序如下。


import java.io.IOException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.util.Bytes;

import org.apache.hadoop.hbase.client.HTable;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;


public class ScanTable{

   public static void main(String args[]) throws IOException{

      // Instantiating Configuration class
      Configuration config = HBaseConfiguration.create();

      // Instantiating HTable class
      HTable table = new HTable(config, "emp");

      // Instantiating the Scan class
      Scan scan = new Scan();

      // Scanning the required columns
      scan.addColumn(Bytes.toBytes("personal"), Bytes.toBytes("name"));
      scan.addColumn(Bytes.toBytes("personal"), Bytes.toBytes("city"));

      // Getting the scan result
      ResultScanner scanner = table.getScanner(scan);

      // Reading values from scan result
      for (Result result = scanner.next(); result != null; result = scanner.next())

      System.out.println("Found row : " + result);
      //closing the scanner
      scanner.close();
   }
}

编译并执行上述程序，如下所示。


$javac ScanTable.java
$java ScanTable

以下应该是输出：


Found row : keyvalues={2/personal data:city/1609724365298/Put/vlen=7/seqid=0, 2/personal data:name/1609724347682/Put/vlen=4/seqid=0}
Found row : keyvalues={3/personal data:city/1609724457831/Put/vlen=5/seqid=0, 3/personal data:name/1609724433117/Put/vlen=6/seqid=0}
Found row : keyvalues={row1/personal data:city/1609730663707/Put/vlen=5/seqid=0}