Question

我正在尝试从txt文件中读取并写入HBase。

Job Class
   Job job = new Job(conf, "HWriterJob");
        job.setJarByClass(HWriterJob.class);
        FileInputFormat.setInputPaths(job, new Path(otherArgs[0]));

        job.setMapperClass(TokenizerMapper.class);
        job.setOutputKeyClass(ImmutableBytesWritable.class);
        job.setOutputValueClass(Put.class);

        TableMapReduceUtil.initTableReducerJob(table,null,job);

Mapper Class
@Override
    public void map(Text key, Text value, Context context)
            throws IOException, InterruptedException {

        String line = value.toString();

        StringTokenizer st = new StringTokenizer(line, "|");
        String result[] = new String[st.countTokens()];
        int i = 0;
        while (st.hasMoreTokens()) {
            result[i] = st.nextToken();
            i++;
        }

        Map<ImmutableBytesWritable,Put> resultSet = writeToHBase(result);

        for (Map.Entry<ImmutableBytesWritable,Put> entry : resultSet.entrySet()) {
            context.write(new Text(entry.getValue().getRow()), entry.getValue());
        }
    }

Reducer Class

public void reduce(Text key, Iterable<Put> values, Context context)
            throws IOException, InterruptedException {

        for (Put val : values) {
            context.write(key, val);
        }
    }

但我没有做到这一点。

我收到以下错误java.lang.ClassCastException：org.apache.hadoop.io.LongWritable无法强制转换为org.apache.hadoop.io.Text

Answer 1

显然，MR默认为LongWritable作为MapOutputKeyClass，在你的情况下应该是Text，因此应该是错误。

尝试设置 job.setMapOutputKeyClass（Text.class）和还适当地设置了job.setMapOutputValueClass。

Answer 2

            @Job Class
            Job job = new Job(conf, "HWriterJob");
    job.setJarByClass(HWriterJob.class);
    FileInputFormat.setInputPaths(job, new Path(otherArgs[0]));

    job.setMapperClass(TokenizerMapper.class);
    TextInputFormat.setInputPaths(job, new Path(args[0]));
    job.setInputFormatClass(TextInputFormat.class);
    job.setOutputKeyClass(ImmutableBytesWritable.class);
        job.setOutputValueClass(Put.class);
    job.setOutputFormatClass(TableOutputFormat.class);

    job.setNumReduceTasks(0);
    System.exit(job.waitForCompletion(true) ? 0 : 1);
            @Mapper 
            Map<ImmutableBytesWritable,Put> resultSet = writeToHBase(result);

    for (Map.Entry<ImmutableBytesWritable,Put> entry : resultSet.entrySet()) {
        context.write(entry.getKey(), entry.getValue());
    }

从txt文件读取并写入HBase

2 个答案: