运行HBase时常会遇到个错误，我就有这样的经历。
ERROR: org.apache.hadoop.hbase.MasterNotRunningException: Retried 7 times
检查日志：org.apache.hadoop.ipc.RPC$VersionMismatch: Protocol org.apache.hadoop.hdfs.protocol.ClientProtocol version mismatch. (client = 42, server = 41)
如果是这个错误，说明RPC协议不一致所造成的，解决方法：将hbase/lib目录下的hadoop-core的jar文件删除，将hadoop目录下的hadoop-0.20.2-core.jar拷贝到hbase/lib下面，然后重新启动hbase即可。第二种错误是：没有启动hadoop，先启用hadoop，再启用hbase。
在Eclipse开发中，需要加入hadoop所有的jar包以及HBase二个jar包（hbase，zooKooper）。
HBase基础可见帖子：http://www.cnblogs.com/liqizhou/archive/2012/05/14/2499112.html
- 建表，通过HBaseAdmin类中的create静态方法来创建表。
- HTable类是操作表，例如，静态方法put可以插入数据，该类初始化时可以传递一个行键，静态方法getScanner()可以获得某一列上的所有数据，返回Result类,Result类中有个静态方法getFamilyMap（）可以获得以列名为key，值为value，这刚好与hadoop中map结果是一样的。
package test; import java.io.IOException; import java.util.Map; 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.client.HBaseAdmin; import org.apache.hadoop.hbase.client.HTable; import org.apache.hadoop.hbase.client.Put; import org.apache.hadoop.hbase.client.Result; public class Htable { /** * @param args */ public static void main(String[] args) throws IOException { // TODO Auto-generated method stub Configuration hbaseConf = HBaseConfiguration.create(); HBaseAdmin admin = new HBaseAdmin(hbaseConf); HTableDescriptor htableDescriptor = new HTableDescriptor("table" .getBytes()); //set the name of table htableDescriptor.addFamily(new HColumnDescriptor("fam1")); //set the name of column clusters admin.createTable(htableDescriptor); //create a table HTable table = new HTable(hbaseConf, "table"); //get instance of table. for (int i = 0; i < 3; i++) { //for is number of rows Put putRow = new Put(("row" + i).getBytes()); //the ith row putRow.add("fam1".getBytes(), "col1".getBytes(), "vaule1" .getBytes()); //set the name of column and value. putRow.add("fam1".getBytes(), "col2".getBytes(), "vaule2" .getBytes()); putRow.add("fam1".getBytes(), "col3".getBytes(), "vaule3" .getBytes()); table.put(putRow); } for(Result result: table.getScanner("fam1".getBytes())){//get data of column clusters for(Map.Entry<byte[], byte[]> entry : result.getFamilyMap("fam1".getBytes()).entrySet()){//get collection of result String column = new String(entry.getKey()); String value = new String(entry.getValue()); System.out.println(column+","+value); } } admin.disableTable("table".getBytes()); //disable the table admin.deleteTable("table".getBytes()); //drop the tbale } }
以上代码不难看懂。
下面介绍一下，用mapreduce怎样操作HBase，主要对HBase中的数据进行读取。
现在有一些大的文件，需要存入HBase中，其思想是先把文件传到HDFS上，利用map阶段读取<key,value>对，可在reduce把这些键值对上传到HBase中。
package test; import java.io.IOException; import org.apache.hadoop.io.LongWritable; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Mapper; public class MapperClass extends Mapper<LongWritable,Text,Text,Text>{ public void map(LongWritable key,Text value,Context context)thorws IOException{ String[] items = value.toString().split(" "); String k = items[0]; String v = items[1]; context.write(new Text(k), new Text(v)); } }
Reduce类,主要是将键值传到HBase表中
package test; import java.io.IOException; import org.apache.hadoop.hbase.client.Put; import org.apache.hadoop.hbase.io.ImmutableBytesWritable; import org.apache.hadoop.hbase.mapreduce.TableReducer; import org.apache.hadoop.io.Text; public class ReducerClass extends TableReducer<Text,Text,ImmutableBytesWritable>{ public void reduce(Text key,Iterable<Text> values,Context context){ String k = key.toString(); StringBuffer str=null; for(Text value: values){ str.append(value.toString()); } String v = new String(str); Put putrow = new Put(k.getBytes()); putrow.add("fam1".getBytes(), "name".getBytes(), v.getBytes()); } }
由上面可知ReducerClass继承TableReduce，在hadoop里面ReducerClass继承Reducer类。它的原型为：TableReducer<KeyIn,Values,KeyOut>可以看出，HBase里面是读出的Key类型是ImmutableBytesWritable。
Map，Reduce，以及Job的配置分离，比较清晰,mahout也是采用这种构架。
package test; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.conf.Configured; import org.apache.hadoop.fs.Path; import org.apache.hadoop.hbase.HBaseConfiguration; import org.apache.hadoop.hbase.mapreduce.TableMapReduceUtil; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.input.TextInputFormat; import org.apache.hadoop.util.Tool; public class Driver extends Configured implements Tool{ @Override public static void run(String[] arg0) throws Exception { // TODO Auto-generated method stub Configuration conf = HBaseConfiguration.create(); conf.set("hbase.zookeeper.quorum.", "localhost"); Job job = new Job(conf,"Hbase"); job.setJarByClass(TxtHbase.class); Path in = new Path(arg0[0]); job.setInputFormatClass(TextInputFormat.class); FileInputFormat.addInputPath(job, in); job.setMapperClass(MapperClass.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(Text.class); TableMapReduceUtil.initTableReducerJob("table", ReducerClass.class, job); job.waitForCompletion(true); } }
Driver中job配置的时候没有设置 job.setReduceClass(); 而是用 TableMapReduceUtil.initTableReducerJob(“tab1”, THReducer.class, job); 来执行reduce类。
主函数
package test; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.util.ToolRunner; public class TxtHbase { public static void main(String [] args) throws Exception{
Driver.run(new Configuration(),new THDriver(),args);
}
}
读取数据时比较简单，编写Mapper函数，读取<key,value>值就行了。
package test; import java.io.IOException; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.hbase.client.Result; import org.apache.hadoop.hbase.io.ImmutableBytesWritable; import org.apache.hadoop.hbase.mapred.TableMap; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapred.MapReduceBase; import org.apache.hadoop.mapred.OutputCollector; import org.apache.hadoop.mapred.Reporter; public class MapperClass extends MapReduceBase implements TableMap<Text, Text> { static final String NAME = "GetDataFromHbaseTest"; private Configuration conf; public void map(ImmutableBytesWritable row, Result values, OutputCollector<Text, Text> output, Reporter reporter) throws IOException { StringBuilder sb = new StringBuilder(); for (Entry<byte[], byte[]> value : values.getFamilyMap( "fam1".getBytes()).entrySet()) { String cell = value.getValue().toString(); if (cell != null) { sb.append(new String(value.getKey())).append(new String(cell)); } } output.collect(new Text(row.get()), new Text(sb.toString())); }
要实现这个方法 initTableMapJob(String table, String columns, Class<? extends TableMap> mapper, Class<? extends org.apache.hadoop.io.WritableComparable> outputKeyClass, Class<? extends org.apache.hadoop.io.Writable> outputValueClass, org.apache.hadoop.mapred.JobConf job, boolean addDependencyJars)。
package test; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.conf.Configured; import org.apache.hadoop.fs.Path; import org.apache.hadoop.hbase.HBaseConfiguration; import org.apache.hadoop.hbase.mapreduce.TableMapReduceUtil; import org.apache.hadoop.io.Text; import org.apache.hadoop.mapreduce.Job; import org.apache.hadoop.mapreduce.lib.input.FileInputFormat; import org.apache.hadoop.mapreduce.lib.input.TextInputFormat; import org.apache.hadoop.util.Tool; public class Driver extends Configured implements Tool{ @Override public static void run(String[] arg0) throws Exception { // TODO Auto-generated method stub Configuration conf = HBaseConfiguration.create(); conf.set("hbase.zookeeper.quorum.", "localhost"); Job job = new Job(conf,"Hbase"); job.setJarByClass(TxtHbase.class); job.setInputFormatClass(TextInputFormat.class); job.setMapOutputKeyClass(Text.class); job.setMapOutputValueClass(Text.class);
TableMapReduceUtilinitTableMapperJob("table", args0[0],MapperClass.class, job);
job.waitForCompletion(true); }
}
主函数
package test; import org.apache.hadoop.conf.Configuration; import org.apache.hadoop.util.ToolRunner; public class TxtHbase { public static void main(String [] args) throws Exception{ Driver.run(new Configuration(),new THDriver(),args); } }
作者：BIGBIGBOAT/Liqizhou
