1，代碼

package mr;

import java.io.IOException;

import org.apache.commons.lang.StringUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.ArrayWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.Writable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

 
/**
 * 使用ArrayWritable
 */
public class TrafficApp4 {

    public static void main(String[] args) throws Exception{
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf , TrafficApp4.class.getSimpleName());
        job.setJarByClass(TrafficApp4.class);
        
        FileInputFormat.setInputPaths(job, args[
 
0]);
        job.setMapperClass(TrafficMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongArrayWritable.class);
        
        job.setReducerClass(TrafficReducer.class);
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(LongArrayWritable.
 
class);
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        
        job.waitForCompletion(true);
    }
    
    
    public static class TrafficMapper extends Mapper<LongWritable, Text, Text, LongArrayWritable>{
        @Override
        protected void map(LongWritable key, Text value,
                Mapper<LongWritable, Text, Text, LongArrayWritable>.Context context)
                        throws IOException, InterruptedException {
            String line = value.toString();
            String[] splited = line.split("\t");
            String phonenumber = splited[1];
            
            String upPackNum = splited[6];
            String downPackNum = splited[7];
            String upPayLoad = splited[8];
            String downPayLoad = splited[9];
            
            Text k2 = new Text(phonenumber);
            LongArrayWritable v2 = new LongArrayWritable(upPackNum, downPackNum, upPayLoad, downPayLoad);
            context.write(k2, v2);
        }
    }
    
    public static class TrafficReducer extends Reducer<Text, LongArrayWritable, Text, LongArrayWritable>{
        @Override
        protected void reduce(Text k2, Iterable<LongArrayWritable> v2s,
                Reducer<Text, LongArrayWritable, Text, LongArrayWritable>.Context context)
                        throws IOException, InterruptedException {
            
            long upPackNum = 0L;
            long downPackNum = 0L;
            long upPayLoad = 0L;
            long downPayLoad = 0L;
            for (LongArrayWritable v2 : v2s) {
                Writable[] values = v2.get();
                upPackNum += ((LongWritable)values[0]).get();
                downPackNum += ((LongWritable)values[1]).get();
                upPayLoad += ((LongWritable)values[2]).get();
                downPayLoad += ((LongWritable)values[3]).get();
            }
            
            LongArrayWritable v3 = new LongArrayWritable(upPackNum, downPackNum, upPayLoad, downPayLoad);
            context.write(k2, v3);
        }
    }
    
    public static class LongArrayWritable extends ArrayWritable{
        /**
         * 在調用的時候，首先調用該方法，然後調用set(Writable[])
         */
        public LongArrayWritable() {
            super(LongWritable.class);
        }
        /**
         * 直接調用該方法即可
         * @param values
         */
        public LongArrayWritable(LongWritable[] values) {
            super(LongWritable.class, values);
        }
        /**
         * 直接調用該方法即可
         * @param upPackNum
         * @param downPackNum
         * @param upPayLoad
         * @param downPayLoad
         */
        public LongArrayWritable(Long upPackNum, Long downPackNum, Long upPayLoad, Long downPayLoad) {
            super(LongWritable.class);
            LongWritable[] values = new LongWritable[4];
            values[0] = new LongWritable(upPackNum);
            values[1] = new LongWritable(downPackNum);
            values[2] = new LongWritable(upPayLoad);
            values[3] = new LongWritable(downPayLoad);
            super.set(values);
        }
        /**
         * 直接調用該方法即可
         * @param upPackNum
         * @param downPackNum
         * @param upPayLoad
         * @param downPayLoad
         */
        public LongArrayWritable(String upPackNum, String downPackNum, String upPayLoad, String downPayLoad) {
            super(LongWritable.class);
            LongWritable[] values = new LongWritable[4];
            values[0] = new LongWritable(Long.parseLong(upPackNum));
            values[1] = new LongWritable(Long.parseLong(downPackNum));
            values[2] = new LongWritable(Long.parseLong(upPayLoad));
            values[3] = new LongWritable(Long.parseLong(downPayLoad));
            super.set(values);
        }
        
        @Override
        public String toString() {
            String[] array =  super.toStrings();
            return StringUtils.join(array, "\t");
        }
    }
    
}

2，ArrayWritable的API

org.apache.hadoop.io
Class ArrayWritable

java.lang.Object
  

org.apache.hadoop.io.ArrayWritable

已實現的接口：

Writable

public class ArrayWritableextends Objectimplements Writable

A Writable for arrays containing instances of a class. The elements of this writable must all be instances of the same class. If this writable will be the input for a Reducer, you will need to create a subclass that sets the value to be of the proper type. For example: public class IntArrayWritable extends ArrayWritable { public IntArrayWritable() { super(IntWritable.class); } }

ArrayWritable

public ArrayWritable(Class<? extends Writable> valueClass)

ArrayWritable

public ArrayWritable(Class<? extends Writable> valueClass,
                     Writable[] values)

ArrayWritable

public ArrayWritable(String[] strings)

getValueClass

public Class getValueClass()

toStrings

public String[] toStrings()

toArray

public Object toArray()

set

public void set(Writable[] values)

get

public Writable[] get()

readFields

public void readFields(DataInput in)
                throws IOException

Description copied from interface: Writable

Deserialize the fields of this object from in.

For efficiency, implementations should attempt to re-use storage in the existing object where possible.

Specified by:

readFields in interface Writable

Parameters:

in - DataInput to deseriablize this object from.

Throws:

IOException

write

public void write(DataOutput out)
           throws IOException

Description copied from interface: Writable

Serialize the fields of this object to out.

Specified by:

write in interface Writable

Parameters:

out - DataOuput to serialize this object into.

Throws:

IOException

基於MapReduce的手機流量統計分析