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,IOS7 1512,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 mavericks 1101,macbook pro,苹果,OS X lion 1101,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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