HBase掃描

scan 命令用於查看HTable數據。使用 scan 命令可以得到表中的數據。它的語法如下：

scan ‘<table name>’

下面的示例演示瞭如何使用scan命令從表中讀取數據。在這裏讀取的是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掃描

使用Java API掃描整個表的數據的完整程序如下：

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(); } }

編譯和執行上述程序如下所示。

$javac ScanTable.java
$java ScanTable

下面列出的是輸出：

Found row :
keyvalues={row1/personal:city/1418275612888/Put/vlen=5/mvcc=0,
row1/personal:name/1418035791555/Put/vlen=4/mvcc=0}