HBase应用程序开发01创建表

hbase-1.1.3

hadoop-2.5.2

zookeeper-3.4.6

在HBase测试的时候出现HBaseConfiguration为null;

ClassLoader cc =  HBaseConfiguration.class.getClassLoader();
System.out.println(cc);

显示cc为null;

有网友说是jar引入错了

将hbase的jar删除， 重新引入

结果正常了， 可以创建表了，

出现新的错误：

log4j:ERROR Could not find value for key log4j.appender.Console
log4j:ERROR Could not instantiate appender named "Console".
log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.

网上说要配置log4j.properties文件， 我也配置了， 仍然报错

一、创建表

代码如下

package com.chb.hbase;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.Admin;
import org.apache.hadoop.hbase.client.Connection;
import org.apache.hadoop.hbase.client.ConnectionFactory;

public class TestHbase {
public static Connection conn = null;
public static TableName tableName = TableName.valueOf("tb_phone");

public static void create() throws IOException {
Configuration conf = HBaseConfiguration.create();
conn = ConnectionFactory.createConnection(conf);
Admin admin = conn.getAdmin();
if (admin.tableExists(tableName)) {
admin.disableTable(tableName);
admin.deleteTable(tableName);
}
HTableDescriptor htd = new HTableDescriptor(tableName);
HColumnDescriptor hcd = new HColumnDescriptor("f1".getBytes());
htd.addFamily(hcd);
admin.createTable(htd);

}
public static void main(String[] args) throws IOException {
System.setProperty("HADOOP_USER_NAEM", "chb");
create();
}

}

1、HBaseConfiguration

  用来加载hbase的配置文件到Configuration

2、Connection 连接类

一个集群的Connection封装了到实际Server的低级Connection和一个与Zookeeper的Connection.

Connection通过ConnectionFactory类实例化

conn = ConnectionFactory.createConnection(conf);

Connection 的生命周期是由调用者管理， 可以通过close（）来释放连接资源。

Connection对象包含内容：

The connection object contains logic to

find the master, 查找主节点

locate regions out on the cluster 定位集群中的region

keeps a cache of locations and then knows how to re-calibrate after they move.

The individual connections to servers, meta cache, zookeeper connection, etc are all shared by the Table and Admin instances obtained from this connection.

在Hbase-1.1.3中提示Hxx类已经被遗弃

/*
* Implementation notes:
*  - Only allow new style of interfaces:
*   -- All table names are passed as TableName. No more byte[] and string arguments
*   -- Most of the classes with names H is deprecated in favor of non-H versions
*   (Table, Connection vs HConnection, etc)
*   -- Only real client-facing public methods are allowed
*  - Connection should contain only getTable(), getAdmin() kind of general methods.
*/

Connection的创建时一个重量级的操作，Connection的实现都是thread-safe，所以client可以创建一个connection，供不同的线程使用。

Table和Admin的实例，都是light-weight and are not thread-safe.

通常，每个客户端应用实例化一个connection, 每个线程都会获取自己的Table。

Caching or pooling of Table and Admin is not recommended.

3、Admin

是HBase的管理API,

实例化, 通过Connection.getAdmin();

Admin admin = conn.getAdmin();

Admin的功能：

Admin can be used to create, drop, list, enable and disable tables, add and drop table column families and other administrative operations.

如判断表的存在， 删除：

删除表： 首先disable tableName, 然后 drop tableName

if (admin.tableExists(tableName)) {
admin.disableTable(tableName);
admin.deleteTable(tableName);
}

HColumnDescriptor

列簇的信息， 包含列簇的详细信息,如：version, compression 等。

It is used as input when creating a table or adding a column

通常作为一个输入， 用来创建表或添加一个column.

HTableDescriptor

表的描述信息

通过HTableDescriptor的对象调用addFammiy(HColumnDeescriptor)来加载一个列簇

HColumnDescriptor hcd = new HColumnDescriptor("f1".getBytes());
HTableDescriptor htd = new HTableDescriptor(tableName);
htd.addFamily(hcd);

通过Admin.createTable(HTableDescriptor)来创建一个表

admin.createTable(htd);

关闭Connection

//关闭连接
conn.close();

完整代码：

package com.chb.hbase;

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.Admin;
import org.apache.hadoop.hbase.client.Connection;
import org.apache.hadoop.hbase.client.ConnectionFactory;

public class TestHbase {
public static Connection conn = null;
public static TableName tableName = TableName.valueOf("tb_phone");

public static void create() throws IOException {
Configuration conf = HBaseConfiguration.create();
conn = ConnectionFactory.createConnection(conf);
Admin admin = conn.getAdmin();
if (admin.tableExists(tableName)) {
admin.disableTable(tableName);
admin.deleteTable(tableName);
}
HColumnDescriptor hcd = new HColumnDescriptor("f1".getBytes());
HTableDescriptor htd = new HTableDescriptor(tableName);
htd.addFamily(hcd);
admin.createTable(htd);
//关闭连接
conn.close();
}
public static void main(String[] args) throws IOException {
System.setProperty("HADOOP_USER_NAEM", "chb");
create();
}

}