这些天研究HBase，写了一段Demo代码，具体如下：

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@Test
public void doTest() throws MasterNotRunningException, ZooKeeperConnectionException, IOException {
	Configuration config = HBaseConfiguration.create();
	config.set(zkSetKey, zkConn);
	HBaseAdmin hBaseAdmin = null;
	try{
		hBaseAdmin = new HBaseAdmin(config);
		ClusterStatus clusterStatus = hBaseAdmin.getClusterStatus();
		ServerName master = clusterStatus.getMaster();
		log.info("Master主机:{},端口号:{}", master.getHostname(), master.getPort());
		Collection servers = clusterStatus.getServers();
		for (ServerName serverName : servers) {
			log.info("Region主机{},端口号:{}", serverName.getHostname(), serverName.getPort());
		}
		HTableDescriptor targetTableDesc = null;
		try{
			targetTableDesc = hBaseAdmin.getTableDescriptor(TableName.valueOf(tableName));
			log.info("表已经存在,显示信息");
			log.info("属性:{}", targetTableDesc.toString());
		}catch(TableNotFoundException notFound){
			log.info("表不存在,创建");
			HTableDescriptor htd = new HTableDescriptor(TableName.valueOf(tableName));
			HColumnDescriptor hcd_info = new HColumnDescriptor("info");
			hcd_info.setMaxVersions(3);
			HColumnDescriptor hcd_data = new HColumnDescriptor("data");
			htd.addFamily(hcd_info);
			htd.addFamily(hcd_data);
			hBaseAdmin.createTable(htd);
			log.info("创建成功");
			targetTableDesc = hBaseAdmin.getTableDescriptor(TableName.valueOf(tableName));
			log.info("属性:{}", targetTableDesc.toString());
		}
		TableName[] listTableNames = hBaseAdmin.listTableNames();
		if (listTableNames == null){
			log.info("无表");
		}else{
			for (TableName tableName : listTableNames) {
				log.info("表名:{}", tableName.getNameAsString());
			}
		}
	}finally{
		IOUtils.closeQuietly(hBaseAdmin);
		log.info("结束");
	}
}

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在CSDN找到了一种类似的情况：http://blog.csdn.net/lxpbs8851/article/details/8287471

主要是说HBase所依赖的HDFS进入了安全模式，需要手动退出该模式（运行命令：hdfs dfsadmin -safemode leave）。可是我查询当前的HDFS安全模式状态（hdfs dfsadmin -safemode get）时得到的信息是：Safe mode is OFF，也就是说根本没在安全模式下。

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后来偶然地过了一段时间再去看日志发现如下信息：

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#1, waiting for some tasks to finish. Expected max=0, tasksSent=9, tasksDone=8, currentTasksDone=8, retries=8 hasError=false, tableName=demo_table
#1, waiting for some tasks to finish. Expected max=0, tasksSent=10, tasksDone=9, currentTasksDone=9, retries=9 hasError=false, tableName=demo_table
#1, table=demo_table, attempt=10/35 failed 1 ops, last exception: java.net.UnknownHostException: unknown host: admin.demo.com on admin.demo.cn,5020,1426211698289, tracking started Fri Mar 13 11:41:19 CST 2015, retrying after 10037 ms, replay 1 ops.

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最后一行的主机名：admin.demo.com和admin.demo.cn引起了我的注意。因为我的测试环境为3台实体服务器，配置如下：

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192.168.1.22 admin.demo.com
192.168.1.22 admin.demo.cn