MapReduce操作HBase

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

1. 建表，通过HBaseAdmin类中的create静态方法来创建表。
2. 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。

3. 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 stubConfiguration hbaseConf = HBaseConfiguration.create();HBaseAdmin admin = new HBaseAdmin(hbaseConf);HTableDescriptor htableDescriptor = new HTableDescriptor("table".getBytes());  //set the name of tablehtableDescriptor.addFamily(new HColumnDescriptor("fam1")); //set the name of column clustersadmin.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 rowsPut putRow = new Put(("row" + i).getBytes()); //the ith rowputRow.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 resultString column = new String(entry.getKey());String value = new String(entry.getValue());System.out.println(column+","+value);}}admin.disableTable("table".getBytes()); //disable the tableadmin.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{@Overridepublic static void run(String[] arg0) throws Exception {// TODO Auto-generated method stubConfiguration 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 implementsTableMap<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{@Overridepublic static void run(String[] arg0) throws Exception {// TODO Auto-generated method stubConfiguration 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); } 
}

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 作者：BIGBIGBOAT/Liqizhou