Hbase 简明教程
HBase - Scan
Scaning using HBase Shell
scan 命令用于查看 HTable 中的数据。使用 scan 命令,您可以获取表数据。它的语法如下:
scan ‘<table name>’
Example
以下示例演示如何使用 scan 命令从表中读取数据。这里我们正在读取 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
Scanning Using Java API
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
输出应如下所示:
Found row :
keyvalues={row1/personal:city/1418275612888/Put/vlen=5/mvcc=0,
row1/personal:name/1418035791555/Put/vlen=4/mvcc=0}