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scan 命令用于查看HTable数据。使用 scan 命令可以得到表中的数据。它的语法如下：
下面的示例演示了如何使用scan命令从表中读取数据。在这里读取的是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扫描
使用Java API扫描整个表的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();
}
} |
编译和执行上述程序如下所示。
$javac ScanTable.java
$java ScanTable |
下面列出的是输出：
Found row :
keyvalues={row1/personal:city/1418275612888/Put/vlen=5/mvcc=0,
row1/personal:name/1418035791555/Put/vlen=4/mvcc=0} |
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