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}