OutputFormat接口實(shí)現(xiàn)類

OutputFormat是MapReduce輸出的基類，所有實(shí)現(xiàn)MapReduce輸出都實(shí)現(xiàn)了OutputFormat接口梅垄。

3.1 OutputFormat接口實(shí)現(xiàn)類.png

默認(rèn)輸出格式TextOutputFormat

自定義OutputFormat

1）應(yīng)用場景

輸出數(shù)據(jù)到MySQL/HBase/ES等存儲(chǔ)框架中。

2）自定義OutputFormat步驟

• 自定義一個(gè)類繼承FileOutputFormat刮刑。

• 重寫RecordWriter毅戈，具體重寫輸出數(shù)據(jù)的方法write()夯秃。

實(shí)戰(zhàn)

LogRecordWriter.java

public class LogRecordWriter extends RecordWriter<Text, NullWritable> {

    private FSDataOutputStream oneOut;
    private FSDataOutputStream otherOut;

    public LogRecordWriter(TaskAttemptContext job) {
        // 創(chuàng)建流
        try {
            FileSystem fileSystem = FileSystem.get(job.getConfiguration());
            oneOut = fileSystem.create(
                new Path(System.getProperty("user.dir")+"/output/outputfromat/one.txt"));
            otherOut = fileSystem.create(
                new Path(System.getProperty("user.dir")+"/output/outputfromat/other.txt"));

        } catch (IOException e) {
            e.printStackTrace();
        }

    }

    @Override
    public void write(Text key, NullWritable value) throws IOException, InterruptedException {
        // 具體寫
        String line = key.toString();
        if(line.contains("https")){
            oneOut.writeBytes(line+"\n");
        }else{
            otherOut.writeBytes(line+"\n");
        }
    }

    @Override
    public void close(TaskAttemptContext context) throws IOException, InterruptedException {
        IOUtils.closeStream(oneOut);
        IOUtils.closeStream(otherOut);
    }
}

LogOutputFormat.java

public class LogOutputFormat extends FileOutputFormat<Text, NullWritable> {

    @Override
    public RecordWriter<Text, NullWritable> getRecordWriter(TaskAttemptContext job)
        throws IOException, InterruptedException {
        LogRecordWriter logRecordWriter = new LogRecordWriter(job);
        return logRecordWriter;
    }
}

LogMapper.java

public class LogMapper extends Mapper<LongWritable, Text, Text, NullWritable> {

    @Override
    protected void map(LongWritable key, Text value,
        Mapper<LongWritable, Text, Text, NullWritable>.Context context)
        throws IOException, InterruptedException {
        context.write(value, NullWritable.get());
    }
}

LogReducer.java

public class LogReducer  extends Reducer<Text, NullWritable, Text, NullWritable> {

    @Override
    protected void reduce(Text key, Iterable<NullWritable> values,
        Reducer<Text, NullWritable, Text, NullWritable>.Context context)
        throws IOException, InterruptedException {
        for (NullWritable value : values) {
            context.write(key,NullWritable.get());
        }
    }
}

LogDriver.java

public class LogDriver {

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);

        job.setJarByClass(LogDriver.class);
        job.setMapperClass(LogMapper.class);
        job.setReducerClass(LogReducer.class);

        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(NullWritable.class);

        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(NullWritable.class);

        // 設(shè)置自定義的OutputFormat
        job.setOutputFormatClass(LogOutputFormat.class);

        FileInputFormat.setInputPaths(job, new Path(System.getProperty("user.dir")+"/input/outputfromat"));
        // 雖然我們定義類OutputFormat，但是因?yàn)槲覀兊腛utputFormat繼承自FileOutputFormat
        // 而FileOutputFormat要輸出一個(gè)_SUCCESS文件徽惋，所以還得指定一個(gè)輸出目錄
        FileOutputFormat.setOutputPath(job, new Path(System.getProperty("user.dir")+"/output/outputfromat"));

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

}

代碼gitee地址

小結(jié)

本節(jié)我們了解到了OutputFormat數(shù)據(jù)輸出疆拘，認(rèn)識(shí)到自定義輸出流。在實(shí)際應(yīng)用中寂曹，F(xiàn)ileOutputFormat并不能完全滿足需求，可以通過繼承OutputFormat來自定義輸出回右。