二次排序代码实现

//map类，实现map类

public class MyMapper extends Mapper{
		private IntWritable outputValue = new IntWritable();
		Student stu = new Student();
		@Override
		protected void map(Object key, Text value,Context context)
				throws IOException, InterruptedException {
		String[] arr = value.toString().split(" ");
		stu.setNo(arr[0]);
		stu.setScore(Integer.parseInt(arr[1]));
		outputValue.set(Integer.parseInt(arr[1]));
		context.write(stu, outputValue);
		}
	}

//自定义分区类，保证同key的记录，能映射到相同的reduce端去处理

public class MyPartioner extends Partitioner{

		@Override
		public int getPartition(Student key, IntWritable value,
				int numPartitions) {
			return (key.getNo().hashCode() & Integer.MAX_VALUE) % numPartitions;
		}
	}

//shuffle阶段的sort全局排序完成后，如何对数据记录进行分组

public class shuffleSort extends WritableComparator{

		public shuffleSort() {
			super(Student.class,true);
		}
		@Override
		public int compare(WritableComparable a, WritableComparable b) {
			Student stuA = (Student) a;
			Student stuB = (Student) b;
			return stuA.getNo().compareTo(stuB.getNo());
			//对组合key中的key进行排序
		}
	}

//reduce类，实现reduce函数

public class MyReducer extends Reducer{
		private Text no = new Text();

		@Override
		protected void reduce(Student key, Iterable values, Context context)
				throws IOException, InterruptedException {
			for(IntWritable val:values){
				no.set(key.getNo());
				context.write(no,val);
			}
		}
	}

//启动mr的driver方法

public static void main(String[] args) throws Exception {
		Configuration conf = new Configuration();
		GenericOptionsParser optionsParser = new GenericOptionsParser(conf,args);
		String[] remainArgs = optionsParser.getRemainingArgs();
		if(remainArgs.length != 2){
			System.err.println("Usage: yarn jar jar_path main_class_path -D 参数列表  ");
			System.exit(2);
		}
		Job job = Job.getInstance(conf,"二次排序标准版");
		job.setJarByClass(SecondSort.class);
		job.setPartitionerClass(MyPartioner.class);
		job.setMapperClass(MyMapper.class);
		job.setReducerClass(MyReducer.class);
		job.setCombinerClass(MyReducer.class);
		//设置reduce个数
		job.setNumReduceTasks(2);
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);
		job.setMapOutputKeyClass(Student.class);
		job.setMapOutputValueClass(IntWritable.class);
		FileInputFormat.addInputPath(job, new Path(remainArgs[0]));
		FileOutputFormat.setOutputPath(job, new Path(remainArgs[1]));
		System.exit(job.waitForCompletion(true)?0:1);
	}

实体类

public class Student implements WritableComparable{
	private String no;
	private int score;
	
	public Student(){
		
	}
	public Student(String no, int score) {
		super();
		this.no = no;
		this.score = score;
	}
	public String getNo() {
		return no;
	}
	public void setNo(String no) {
		this.no = no;
	}
	public int getScore() {
		return score;
	}
	public void setScore(int score) {
		this.score = score;
	}
	//序列化
	@Override
	public void write(DataOutput out) throws IOException {
		out.writeUTF(no);
		out.writeInt(score);
		//把基本类型写入流中
		//writeUTF和writeBytes都可以传String类型的参数，而write不可以
	}
	//反序列化
	@Override
	public void readFields(DataInput in) throws IOException {
		no = in.readUTF();
		score = in.readInt();
		
	}
	
	@Override
	public int compareTo(Student o) {
		int val = this.no.compareTo(o.no);
		if(val != 0){
			return 0;
		}
		return Integer.valueOf(o.score).compareTo(Integer.valueOf(this.score));
	}
	
}