1.需求

将学生成绩，按照各个成绩降序排序，各个科目成绩单独输出。

# 自定义partition 将下面数据分区处理：

人名 科目 成绩

张三 语文 10

李四 数学 30

王五 语文 20

赵6 英语 40

张三 数据 50

李四 语文 10

张三 英语 70

李四 英语 80

王五 英语 45

王五 数学 10

赵6 数学 10

赵6 语文 100

2.思路分析

# 自定义分区

1. 编写自定义分区类，继承Partitioner覆盖getPartition方法 注意：分区号从0开始算。

2. 给job注册分区类 【覆盖默认分区】 job.setPartitionerClass(自定义Partitioner.class); 3. 设置ReduceTask个数(开启分区) job.setNumReduceTasks(数字);//reduceTask数量要和分区数量一样。

3.Idea代码

DefinePartitionJob

package demo7;

import demo5.DescIntWritable;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
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.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

import java.io.IOException;

public class DefinePartitionJob {
    public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {

        Configuration conf = new Configuration();
        conf.set("fs.defaultFS","hdfs://hadoop10:8020");

        Job job = Job.getInstance(conf);
        job.setJarByClass(DefinePartitionJob.class);

        job.setInputFormatClass(TextInputFormat.class);
        job.setOutputFormatClass(TextOutputFormat.class);

        TextInputFormat.addInputPath(job,new Path("/mapreduce/demo10"));
        TextOutputFormat.setOutputPath(job,new Path("/mapreduce/demo10/out"));

        job.setMapperClass(DefinePartitonMapper.class);
        job.setReducerClass(DefinePartitonReducer.class);
        //map输出的键与值类型
        job.setMapOutputKeyClass(DescIntWritable.class);
        job.setMapOutputValueClass(Subject.class);
        //reducer输出的键与值类型
        job.setOutputKeyClass(Subject.class);
        job.setOutputValueClass(DescIntWritable.class);

        //设置reduceTask的个数
        job.setNumReduceTasks(4);
        //设置自定义分区
        job.setPartitionerClass(MyPartition.class);

        boolean b = job.waitForCompletion(true);
        System.out.println(b);

    }


    static class DefinePartitonMapper extends Mapper<LongWritable, Text, DescIntWritable,Subject> {
        @Override
        protected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {
            String[] arr = value.toString().split("\t");
            context.write(new DescIntWritable(Integer.parseInt(arr[2])),new Subject(arr[0],arr[1]));
        }
    }
    static class DefinePartitonReducer extends Reducer<DescIntWritable,Subject,Subject,DescIntWritable> {
        @Override
        protected void reduce(DescIntWritable key, Iterable<Subject> values, Context context) throws IOException, InterruptedException {
            for (Subject subject : values) {
                context.write(subject, key);
            }
        }
    }}

MyPartition

package demo7;

import demo5.DescIntWritable;
import org.apache.hadoop.mapreduce.Partitioner;

public class MyPartition extends Partitioner<DescIntWritable,Subject> {
    @Override
    public int getPartition(DescIntWritable key, Subject value, int numPartitions) {
        if ("语文".equals(value.getKemu())){
            return 0;
        }else if ("数学".equals(value.getKemu())) {
            return 1;
        }else if ("英语".equals(value.getKemu())) {
            return 2;
        }
            return 3;


        }
}

 Subject

package demo7;

import org.apache.hadoop.io.Writable;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

public class Subject implements Writable{
    private String name;
    private String kemu;

    public Subject() {
    }

    public Subject(String name, String kemu) {
        this.name = name;
        this.kemu = kemu;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getKemu() {
        return kemu;
    }

    public void setKemu(String kemu) {
        this.kemu = kemu;
    }

    @Override
    public void write(DataOutput out) throws IOException {
        out.writeUTF(name);
        out.writeUTF(kemu);
    }

    @Override
    public void readFields(DataInput in) throws IOException {
        this.name = in.readUTF();
        this.kemu = in.readUTF();

    }

    @Override
    public String toString() {
        return name + " " +kemu;
    }
}

 4.在hdfs查看结果

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