Question

我有一个haddop作业，它的输出应写入HBase。我真的不需要reducer，我想插入的那种行在Mapper中确定。

如何使用TableOutputFormat实现此目的？从我看到的所有示例中，我们假设reducer是创建Put的那个，而TableMapper只是用于从HBase表中读取。

在我的情况下，输入是HDFS，输出是Put到特定的表，我在TableMapReduceUtil中找不到任何可以帮助我的东西。

有没有可以帮助我的例子？

BTW，我正在使用新的Hadoop API

Answer 1

这是从文件读取并将所有行放入Hbase的示例。这个例子来自＆＃34; Hbase：权威指南＆＃34;你可以在存储库中找到它。只需在您的计算机上克隆回购：

git clone git://github.com/larsgeorge/hbase-book.git

在本书中，您还可以找到有关代码的所有说明。但如果你有些不可理解的事情，请随意提问。

`    public class ImportFromFile {
     public static final String NAME = "ImportFromFile"; 
     public enum Counters { LINES }

     static class ImportMapper
     extends Mapper<LongWritable, Text, ImmutableBytesWritable, Writable> { 
       private byte[] family = null;
       private byte[] qualifier = null;

       @Override
       protected void setup(Context context)
         throws IOException, InterruptedException {
         String column = context.getConfiguration().get("conf.column");
         byte[][] colkey = KeyValue.parseColumn(Bytes.toBytes(column));
         family = colkey[0];
         if (colkey.length > 1) {
           qualifier = colkey[1];
         }
       }

       @Override
       public void map(LongWritable offset, Text line, Context context) 
       throws IOException {
          try {
           String lineString = line.toString();
           byte[] rowkey = DigestUtils.md5(lineString); 
           Put put = new Put(rowkey);
           put.add(family, qualifier, Bytes.toBytes(lineString)); 
           context.write(new ImmutableBytesWritable(rowkey), put);
           context.getCounter(Counters.LINES).increment(1);
         } catch (Exception e) {
           e.printStackTrace();
         }
       }
     }

     private static CommandLine parseArgs(String[] args) throws ParseException { 
       Options options = new Options();
       Option o = new Option("t", "table", true,
         "table to import into (must exist)");
       o.setArgName("table-name");
       o.setRequired(true);
       options.addOption(o);
       o = new Option("c", "column", true,
         "column to store row data into (must exist)");
       o.setArgName("family:qualifier");
       o.setRequired(true);
       options.addOption(o);
       o = new Option("i", "input", true,
         "the directory or file to read from");
       o.setArgName("path-in-HDFS");
       o.setRequired(true);
       options.addOption(o);
       options.addOption("d", "debug", false, "switch on DEBUG log level");
       CommandLineParser parser = new PosixParser();
       CommandLine cmd = null;
       try {
         cmd = parser.parse(options, args);
       } catch (Exception e) {
         System.err.println("ERROR: " + e.getMessage() + "\n");
         HelpFormatter formatter = new HelpFormatter();
         formatter.printHelp(NAME + " ", options, true);
         System.exit(-1);
       }
       return cmd;
     }

     public static void main(String[] args) throws Exception {
       Configuration conf = HBaseConfiguration.create();
       String[] otherArgs =
         new GenericOptionsParser(conf, args).getRemainingArgs(); 
       CommandLine cmd = parseArgs(otherArgs);
       String table = cmd.getOptionValue("t");
       String input = cmd.getOptionValue("i");
       String column = cmd.getOptionValue("c");
       conf.set("conf.column", column);
       Job job = new Job(conf, "Import from file " + input + " into table " + table); 

            job.setJarByClass(ImportFromFile.class);
       job.setMapperClass(ImportMapper.class);
       job.setOutputFormatClass(TableOutputFormat.class);
       job.getConfiguration().set(TableOutputFormat.OUTPUT_TABLE, table);
       job.setOutputKeyClass(ImmutableBytesWritable.class);
       job.setOutputValueClass(Writable.class);
       job.setNumReduceTasks(0); 
       FileInputFormat.addInputPath(job, new Path(input));
       System.exit(job.waitForCompletion(true) ? 0 : 1);
     }
    }`

Answer 2

您只需要让映射器输出该对。 OutputFormat仅指定如何保留输出键值。它并不一定意味着关键值来自reducer。您需要在映射器中执行以下操作：

... extends TableMapper<ImmutableBytesWritable, Put>() {
    ...
    ...
    context.write(<some key>, <some Put or Delete object>);
}

Hadoop - 直接从Mapper写入HBase

2 个答案: