HBase概念学习（九）HTablePool为何弃用？

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https://blog.csdn.net/jiq408694711/article/details/36526433

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使用HBase0.94版本号的时候提示HTablePool已经过时了。为什么？

我们先看HConnection的getTable方法描写叙述：

• getTable

  HTableInterface getTable(is-external=true" rel="nofollow" title="class or interface in java.lang">String tableName)
                           throws IOException

  Retrieve an HTableInterface implementation for access to a table. The returned HTableInterface is not thread safe, a new instance should be created for each using thread. This is a lightweight operation, pooling or caching of the returned
  HTableInterface is neither required nor desired. Note that the HConnection needs to be unmanaged (created withHConnectionManager.createConnection(Configuration)).

  Parameters:

  tableName -

  Returns:

  an HTable to use for interactions with this table

  Throws:

  IOException

上面说HTable的的父类HTableInterface是非线程安全的，针对每一个线程建议都应该创建一个新的HTableInterface实例。这个创建过程是轻量的，缓存HTableInterface对象既不是必须的也不是推荐的！

然后再联想到仅仅要HTable使用的Configuration是同一个。那么它们一定是共用一个HConnection的，HConnection才是HBase客户端到Hbase集群的真正的连接。

再想想HTablePool的作用，无非就是HTable的连接池。里面维护的HTable应该来说都是使用的同一个HConnecion。

既然HTable的创建是轻量级的，使用同一个Confuguration的HTable都会共用一个HConnection，那么HTablePool就显得那么多余。

所以Hbase抛弃了HTablePool，我们唯一要做的就是保证HConnection实例是唯一的，全局共享的。然后针对HTableInterface对象最好在每次操作HBase表的时候依据HConnection对象来又一次创建。使用完毕之后及时关闭就可以！

通过HConnection的getTable()方法就行获取到用户操作HBase表的HTableInterface对象了。

以下是一个使用HConnection的getTable()方法获取HTableInterface对象的样例：

public void addUser(User user) throws IOException
	{
		HTableInterface usersTable = conn.getTable(TABLE_NAME);

		Put put = makePut(user);
		usersTable.put(put);

		usersTable.close();
		log.info("Add a User:"+user.name+" successfully");
	}

至于HConnection对象怎样创建，HBase推荐使用的方法是：

• createConnection

  public static HConnection createConnection(org.apache.hadoop.conf.Configuration conf)
                                      throws IOException

  Create a new HConnection instance using the passed conf instance.

  Note: This bypasses the usual HConnection life cycle management done by getConnection(Configuration). The caller is responsible for calling

  is-external=true#close%28%29" rel="nofollow" title="class or interface in java.io">Closeable.close()
  on the returned connection instance. This is the recommended way to create HConnections.HConnection connection = HConnectionManager.createConnection(conf); HTableInterface table = connection.getTable("mytable"); table.get(...); ... table.close(); connection.close();

  Parameters:

  conf - configuration

  Returns:

  HConnection object for conf

  Throws:

  ZooKeeperConnectionException

  IOException

以下代码是我依照单例模式维护HConnection对象的样例：

public class HBaseUtils {

	private static final String QUORUM = "192.168.1.100";
	private static final String CLIENTPORT = "2181";
	private static Configuration conf = null;
	private static HConnection conn = null;

	/**
	 * 获取全局唯一的Configuration实例
	 * @return
	 */
	public static synchronized Configuration getConfiguration()
	{
		if(conf == null)
		{
			conf =  HBaseConfiguration.create();
			conf.set("hbase.zookeeper.quorum", QUORUM);
			conf.set("hbase.zookeeper.property.clientPort", CLIENTPORT);
		}
		return conf;
	}

	/**
	 * 获取全局唯一的HConnection实例
	 * @return
	 * @throws ZooKeeperConnectionException
	 */
	public static synchronized HConnection getHConnection() throws ZooKeeperConnectionException
	{
		if(conn == null)
		{
			/*
			 * * 创建一个HConnection
			 * HConnection connection = HConnectionManager.createConnection(conf);
			 * HTableInterface table = connection.getTable("mytable");
			 * table.get(...); ...
			 * table.close();
			 * connection.close();
			 * */
			conn = HConnectionManager.createConnection(getConfiguration());
		}

		return conn;
	}
}

以上属于个人见解，假设有什么疑问和不吝赐教，欢迎指正。

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