HBase 启用表

• 

  使用HBase Shell 启用表

  要删除表或更改其设置，您需要首先使用enable命令启用该表。您可以使用enable命令重新启用它。

  以下是 启用表的语法：

  
  enable ‘emp’
  

  例下面给出的示例显示了如何 启用表。

  
  hbase(main):025:0> enable 'emp'
  0 row(s) in 1.2760 seconds
  

  验证 - 启用表格后，对其进行扫描。如果可以看到架构，则表已成功启用。

  
  hbase(main):006:0> scan 'emp'
  
     ROW                        COLUMN + CELL
  
  1 column = personal data:city, timestamp = 1417516501, value = hyderabad
  
  1 column = personal data:name, timestamp = 1417525058, value = ramu
  
  1 column = professional data:designation, timestamp = 1417532601, value = manager
  
  1 column = professional data:salary, timestamp = 1417524244109, value = 50000
  
  2 column = personal data:city, timestamp = 1417524574905, value = chennai
  
  2 column = personal data:name, timestamp = 1417524556125, value = ravi
  
  2 column = professional data:designation, timestamp = 14175292204, value = sr:engg
  
  2 column = professional data:salary, timestamp = 1417524604221, value = 30000 
  
  3 column = personal data:city, timestamp = 1417524681780, value = delhi
  
  3 column = personal data:name, timestamp = 1417524672067, value = rajesh
  
  3 column = professional data:designation, timestamp = 14175246987, value = jr:engg
  
  3 column = professional data:salary, timestamp = 1417524702514, value = 25000
  
  3 row(s) in 0.0400 seconds
  

  is_enabled

  此命令用于查找是否启用了表。其语法如下。

  
  hbase> is_enabled 'table name'
  

  下面的示例验证是否启用了名为emp的表。如果启用，它将返回true，否则将返回false。

  
  hbase(main):031:0> is_enabled 'emp'
  true
  0 row(s) in 0.0440 seconds
  

• 

  使用Java API 启用表

  要验证是否启用了表，请使用isTableEnabled（）方法；要 启用表，请使用enableTable（）方法。这些方法属于Admin类。请按照下面给出的步骤 启用表。

  第1步 获得Admin类，如下所示。

  
  // Instantiating configuration class
  Configuration config = HBaseConfiguration.create();
  Connection connection = ConnectionFactory.createConnection(config);
  // Instantiating Admin class
  Admin admin = null;
  admin = connection.getAdmin();
  

  第2步 - 使用isTableEnabled（）方法验证是否启用了该表，如下所示。

  
  Boolean isEnabled =  admin.isTableEnabled(TableName.valueOf("emp"));
  

  第三步 - 如果未启用该表，请如下所示将其启用。

  
  if(!isEnabled) {
     admin.enableTable(TableName.valueOf("emp"));
     System.out.println("Table enabled");
  }
  

  下面给出的是验证表是否已启用的完整程序；如果没有，如何启用它。

  
  import java.io.IOException;
  
  import org.apache.hadoop.hbase.HBaseConfiguration;
  import org.apache.hadoop.hbase.TableName;
  import org.apache.hadoop.hbase.client.Connection;
  import org.apache.hadoop.hbase.client.ConnectionFactory;
  import org.apache.hadoop.hbase.client.Admin;
  
  import org.apache.hadoop.conf.Configuration;
   
  public class CreateTable {
  
     public static void main(String[] args) throws IOException {
        try {
           // Instantiating configuration class
           Configuration config = HBaseConfiguration.create();
           Connection connection = ConnectionFactory.createConnection(config);
           // Instantiating Admin class
           Admin admin = null;
           admin = connection.getAdmin();
   
           Boolean isEnabled =  admin.isTableEnabled(TableName.valueOf("emp"));
           System.out.println(isEnabled);
           
           if(!isEnabled) {
              admin.enableTable(TableName.valueOf("emp"));
              System.out.println("Table enabled");
           }
        } catch (Exception e) {
           System.out.println(e.getMessage());
        }
     }
  }
  

  编译并执行上述程序，如下所示。

  
  $javac EnableTable.java
  $java EnableTable
  

  以下应该是输出：

  
  false
  Table enabled