= hbase 程式範例 =

 = 範例一 =
{{{
#!java

package hbase020;
// WordCountHBase 
//說明： 
//	此程式碼將輸入路徑的檔案內的字串取出做字數統計
// 	再將結果塞回HTable內
//
//運算方法：
//	將此程式運作在hadoop 0.20 平台上，用(參考2)的方法加入hbase參數後，將此程式碼打包成XX.jar 
//  執行：
//	---------------------------
//	hadoop jar XX.jar WordCountHBase <hdfs_input>
//	---------------------------
//
//結果：
// ---------------------------
//	$ hbase shell
//	> scan 'wordcount'
// 	ROW		COLUMN+CELL 
//	am		column=content:count, timestamp=1264406245488, value=1
//  chen	column=content:count, timestamp=1264406245488, value=1 
// 	hi,		column=content:count, timestamp=1264406245488, value=2
//  ......(略)
// ---------------------------
//注意：
//1.	在hdfs 上來源檔案的路徑為 "/user/$YOUR_NAME/input"
//	請注意必須先放資料到此hdfs上的資料夾內，且此資料夾內只能放檔案，不可再放資料夾
//2.	運算完後，程式將執行結果放在hbase的wordcount資料表內
// 
//參考：
//	1.程式碼改編於： http://blog.ring.idv.tw/comment.ser?i=337
//  2.hbase 運作 mapreduce 程式的方法參考於：http://wiki.apache.org/hadoop/Hbase/MapReduce

import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
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.Put;
import org.apache.hadoop.hbase.mapreduce.TableOutputFormat;
import org.apache.hadoop.hbase.mapreduce.TableReducer;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;

public class WordCountHBase {
	public static class HtMap extends
			Mapper<LongWritable, Text, Text, IntWritable> {
		private IntWritable one = new IntWritable(1);

		public void map(LongWritable key, Text value, Context context)
				throws IOException, InterruptedException {
			// 輸入的字串先轉換成小寫再用空白區隔
			String s[] = value.toString().toLowerCase().trim().split(" ");
			for (String m : s) {
				// 寫入到輸出串流
				context.write(new Text(m), one);
			}
		}
	}
	// TableReducer<KEYIN,VALUEIN,KEYOUT> 
	// 原本為 TableReducer<Text, IntWritable, NullWritable > 
	// 但在此改成 LongWritable 也可以
	// 因此證明在此的Class可以很多,org.apache.hadoop.io.* 內有write()的Writable class應該皆可
	public static class HtReduce extends
			TableReducer<Text, IntWritable,LongWritable > {
		
		public void reduce(Text key, Iterable<IntWritable> values,
				Context context) throws IOException, InterruptedException {
			int sum = 0;
			for (IntWritable i : values) {
				sum += i.get();
			}
			
			// org.apache.hadoop.hbase.client.Put 
			// Used to perform Put operations for a single row.
			// new Put(byte[] row) 
			Put put = new Put(Bytes.toBytes(key.toString()));
			
			
			// add(byte[] family, byte[] qualifier, byte[] value)
			// 在main設定output format class 為 TableOutputFormat  
			// TableReducer 內有定義 output Key class 必須為 Put 或 Delete 
			put.add(Bytes.toBytes("content"), Bytes.toBytes("count"), Bytes
					.toBytes(String.valueOf(sum)));
						
			//NullWritable.get(): Returns the single instance of this class.
			//NullWritable.write(): Serialize the fields of this object to out.
			context.write(new LongWritable(), put);
			// context.write(NullWritable.get(), put)
		}
	}

	public static void createHBaseTable(String tablename) throws IOException {
		// HTableDescriptor contains the name of an HTable, and its column
		// families
		// HTableDescriptor 用來描述table的屬性
		HTableDescriptor htd = new HTableDescriptor(tablename);
		// HColumnDescriptor HColumnDescriptor contains information about a
		// column family such as the number of versions, compression settings,
		// etc.
		// HTableDescriptor 透過 add() 方法來加入Column family
		htd.addFamily(new HColumnDescriptor("content:"));
		// HBaseConfiguration 能接收 hbase-site.xml 的設定值
		HBaseConfiguration config = new HBaseConfiguration();
		// 檔案的操作則使用 HBaseAdmin
		HBaseAdmin admin = new HBaseAdmin(config);
		// 檢查
		if (admin.tableExists(tablename)) {
			// 停止
			admin.disableTable(tablename);
			// 刪除
			admin.deleteTable(tablename);
		}
		System.out.println("create new table: " + tablename);
		// 建立
		admin.createTable(htd);
	}

	public static void main(String args[]) throws Exception {
		// debug
		String[] argv = { "/user/waue/input" };
		args = argv;
		String input = args[0];

		String tablename = "wordcount";

		Configuration conf = new Configuration();
		// OUTPUT_TABLE = "hbase.mapred.outputtable"
		// conf.set 用於設定 如 core-site.xml 的 name 與 value
		// 告訴程式 hbase.mapred.outputtable --> wordcount
		conf.set(TableOutputFormat.OUTPUT_TABLE, tablename);
		// 建立hbase 的table 否則沒先建立會出錯
		createHBaseTable(tablename);

		Job job = new Job(conf, "WordCount table with " + input);

		job.setJarByClass(WordCountHBase.class);
		job.setNumReduceTasks(1);
		job.setMapperClass(HtMap.class);
		job.setReducerClass(HtReduce.class);
		// 此範例的輸出為 <Text,IntWritable> 因此其實可以省略宣告 
		// set{Map|Reduce}Output{Key|Value}Class()
		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(IntWritable.class);
		// InputFormat 只有一個子介面
		// FileInputFormat <-(SequenceFileInputFormat,TextInputFormat)
		// 其中TextInputFormat 最常用 ，預設輸入為 LongWritable,Text
		// 另外HBase 則設計了一個子類別 TableInputFormat
		job.setInputFormatClass(TextInputFormat.class);
		// TAbleOutputFormat
		// 宣告此行則可使 reduce 輸出為 HBase 的table
		job.setOutputFormatClass(TableOutputFormat.class);

		// 原本設定輸入檔案為 Config.setInputPath(Path) 卻改為
		// FileInputFormat.addInputPath(Job, Path()) 的設計，
		// 猜測應該是考慮某些檔案操作並不需要跑mapreduce的Job，因此提到外面
		FileInputFormat.addInputPath(job, new Path(input));

		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}
}
}}}


 = 範例二 = 

{{{
#!java

package hbase020;



// 說明：
// 此程式首先建立table, 然後put一個資料後
// 用get 方法取得資料，最後用scan方法取出整個資料表
// 
// 參考： 程式碼改編自
// http://hadoop.apache.org/hbase/docs/current/api/org/apache/.接.
//  hadoop/hbase/client/package-summary.html#package_description

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HColumnDescriptor;
import org.apache.hadoop.hbase.HTableDescriptor;
import org.apache.hadoop.hbase.client.Get;
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;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.util.Bytes;

// Class that has nothing but a main.
// Does a Put, Get and a Scan against an hbase table.
public class MyLittleHBaseClient {
	
	private static String table_name = "mytable";
	
	private static String the_row = "myLittleRow";
	
	private static String column_family = "family";
	
	private static String column_qualifier = "someQualifier";
	
	private static String cell_value = "somvalue";
	
	
	
	public static void createHBaseTable(String tablename) throws IOException {
		// HTableDescriptor contains the name of an HTable, and its column
		// families
		// HTableDescriptor 用來描述table的屬性
		HTableDescriptor htd = new HTableDescriptor(tablename);
		// HColumnDescriptor HColumnDescriptor contains information about a
		// column family such as the number of versions, compression settings,
		// etc.
		// HTableDescriptor 透過 add() 方法來加入Column family
		htd.addFamily(new HColumnDescriptor(column_family+":"));
		// HBaseConfiguration 能接收 hbase-site.xml 的設定值
		HBaseConfiguration config = new HBaseConfiguration();
		// 檔案的操作則使用 HBaseAdmin
		HBaseAdmin admin = new HBaseAdmin(config);
		// 檢查
		if (admin.tableExists(tablename)) {
			// 停止
			admin.disableTable(tablename);
			// 刪除
			admin.deleteTable(tablename);
		}
		System.out.println("create new table: " + tablename);
		// 建立
		admin.createTable(htd);
	}

	public static void main(String[] args) throws IOException {
		// You need a configuration object to tell the client where to connect.
		// When you create a HBaseConfiguration, it reads in whatever you've set
		// into your hbase-site.xml and in hbase-default.xml, as long as these
		// can be found on the CLASSPATH
		
		HBaseConfiguration config = new HBaseConfiguration();

		// create table automatically
		createHBaseTable(table_name);
		
		// This instantiates an HTable object that connects you to
		// the "myLittleHBaseTable" table.
		HTable table = new HTable(config, table_name);


		// To add to a row, use Put. A Put constructor takes the name of the row
		// you want to insert into as a byte array. In HBase, the Bytes class
		// has
		// utility for converting all kinds of java types to byte arrays. In the
		// below, we are converting the String "myLittleRow" into a byte array
		// to
		// use as a row key for our update. Once you have a Put instance, you
		// can
		// adorn it by setting the names of columns you want to update on the
		// row,
		// the timestamp to use in your update, etc.If no timestamp, the server
		// applies current time to the edits.
		Put p = new Put(Bytes.toBytes(the_row));

		// To set the value you'd like to update in the row 'myRow', specify the
		// column family, column qualifier, and value of the table cell you'd
		// like
		// to update. The column family must already exist in your table schema.
		// The qualifier can be anything. All must be specified as byte arrays
		// as
		// hbase is all about byte arrays. Lets pretend the table
		// 'myLittleHBaseTable' was created with a family 'myLittleFamily'.
		p.add(Bytes.toBytes(column_family), Bytes.toBytes(column_qualifier),
				Bytes.toBytes(cell_value));

		// Once you've adorned your Put instance with all the updates you want
		// to
		// make, to commit it do the following (The HTable#put method takes the
		// Put instance you've been building and pushes the changes you made
		// into
		// hbase)
		table.put(p);

		// Now, to retrieve the data we just wrote. The values that come back
		// are
		// Result instances. Generally, a Result is an object that will package
		// up
		// the hbase return into the form you find most palatable.
		Get g = new Get(Bytes.toBytes(the_row));
		Result r = table.get(g);
		byte[] value = r.getValue(Bytes.toBytes(column_family), Bytes
				.toBytes(column_qualifier));
		// If we convert the value bytes, we should get back 'Some Value', the
		// value we inserted at this location.
		String valueStr = Bytes.toString(value);
		System.out.println("GET: " + valueStr);

		// Sometimes, you won't know the row you're looking for. In this case,
		// you
		// use a Scanner. This will give you cursor-like interface to the
		// contents
		// of the table. To set up a Scanner, do like you did above making a Put
		// and a Get, create a Scan. Adorn it with column names, etc.
		Scan s = new Scan();
		s.addColumn(Bytes.toBytes(column_family), Bytes
				.toBytes(column_qualifier));
		ResultScanner scanner = table.getScanner(s);
		try {
			// Scanners return Result instances.
			// Now, for the actual iteration. One way is to use a while loop
			// like so:
			for (Result rr : scanner) {
				// print out the row we found and the columns we were looking
				// for
				System.out.println("Found row: " + rr);
			}

			// The other approach is to use a foreach loop. Scanners are
			// iterable!
			// for (Result rr : scanner) {
			// System.out.println("Found row: " + rr);
			// }
		} finally {
			// Make sure you close your scanners when you are done!
			// Thats why we have it inside a try/finally clause
			scanner.close();
		}
	}
}

}}}