Hadoop MultipleOutputs输出到多个文件中的实现方法

2019-11-26 11:05:28

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Hadoop MultipleOutputs输出到多个文件中的实现方法

1.输出到多个文件或多个文件夹：

驱动中不需要额外改变，只需要在MapClass或Reduce类中加入如下代码

private MultipleOutputs<Text,IntWritable> mos;public void setup(Context context) throws IOException,InterruptedException {　　mos = new MultipleOutputs(context);}public void cleanup(Context context) throws IOException,InterruptedException {　　mos.close();}

　　然后就可以用mos.write(Key key,Value value,String baseOutputPath)代替context.write(key, value);

　　在MapClass或Reduce中使用，输出时也会有默认的文件part-m-00*或part-r-00*，不过这些文件是无内容的，大小为0. 而且只有part-m-00*会传给Reduce。

注意：multipleOutputs.write(key, value, baseOutputPath)方法的第三个函数表明了该输出所在的目录（相对于用户指定的输出目录）。

如果baseOutputPath不包含文件分隔符“/”，那么输出的文件格式为baseOutputPath-r-nnnnn（name-r-nnnnn)；
如果包含文件分隔符“/”，例如baseOutputPath=“029070-99999/1901/part”，那么输出文件则为029070-99999/1901/part-r-nnnnn

2.案例-需求

需求，下面是有些测试数据，要对这些数据按类目输出到output中：

1512,iphone5s,4英寸,指纹识别,A7处理器,64位,M7协处理器,低功耗1512,iphone5,4英寸,A6处理器,IOS71512,iphone4s,3.5英寸,A5处理器,双核,经典50019780,ipad,9.7英寸,retina屏幕,丰富的应用50019780,yoga,联想,待机18小时,外形独特50019780,nexus 7,华硕&google,7英寸50019780,ipad mini 2,retina显示屏,苹果,7.9英寸1101,macbook air,苹果超薄,OS X mavericks1101,macbook pro,苹果,OS X lion1101,thinkpad yoga,联想,windows 8,超级本

3.Mapper程序：

package cn.edu.bjut.multioutput;import java.io.IOException;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Mapper;public class MultiOutPutMapper extends Mapper<LongWritable, Text, IntWritable, Text> {  @Override  protected void map(LongWritable key, Text value, Context context)      throws IOException, InterruptedException {    String line = value.toString().trim();    if(null != line && 0 != line.length()) {      String[] arr = line.split(",");      context.write(new IntWritable(Integer.parseInt(arr[0])), value);    }  }}

4.Reducer程序：

package cn.edu.bjut.multioutput;import java.io.IOException;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.NullWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs;public class MultiOutPutReducer extends    Reducer<IntWritable, Text, NullWritable, Text> {  private MultipleOutputs<NullWritable, Text> multipleOutputs = null;  @Override  protected void reduce(IntWritable key, Iterable<Text> values, Context context)      throws IOException, InterruptedException {    for(Text text : values) {      multipleOutputs.write("KeySpilt", NullWritable.get(), text, key.toString()+"/");      multipleOutputs.write("AllPart", NullWritable.get(), text);    }  }  @Override  protected void setup(Context context)      throws IOException, InterruptedException {    multipleOutputs = new MultipleOutputs<NullWritable, Text>(context);  }  @Override  protected void cleanup(Context context)      throws IOException, InterruptedException {    if(null != multipleOutputs) {      multipleOutputs.close();      multipleOutputs = null;    }  }}

5.主程序：

package cn.edu.bjut.multioutput;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.IntWritable;import org.apache.hadoop.io.NullWritable;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.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.output.MultipleOutputs;import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;public class MainJob {  public static void main(String[] args) throws Exception {    Configuration conf = new Configuration();    Job job = new Job(conf, "aaa");    job.setJarByClass(MainJob.class);    job.setMapperClass(MultiOutPutMapper.class);    job.setMapOutputKeyClass(IntWritable.class);    job.setMapOutputValueClass(Text.class);    job.setReducerClass(MultiOutPutReducer.class);    job.setOutputKeyClass(NullWritable.class);    job.setOutputValueClass(Text.class);    FileInputFormat.addInputPath(job, new Path(args[0]));    MultipleOutputs.addNamedOutput(job, "KeySpilt", TextOutputFormat.class, NullWritable.class, Text.class);    MultipleOutputs.addNamedOutput(job, "AllPart", TextOutputFormat.class, NullWritable.class, Text.class);    Path outPath = new Path(args[1]);    FileSystem fs = FileSystem.get(conf);    if(fs.exists(outPath)) {      fs.delete(outPath, true);    }    FileOutputFormat.setOutputPath(job, outPath);    job.waitForCompletion(true);  }}

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