MapReduce---计数器的使用

• 需求及数据
• 代码实现
• • 自定义Student类
  • 编写Map类
  • 编写DriTest
  • 结果

需求及数据

• 数据

A,40,70,78
B,27,30,84
C,73,88,78
D,75,29,44
E,93,85,15
F,21,4,77
G,50,11,62
H,3,64,18
I,75,31,3
J,38,88,23
K,75,79,26
L,87,69,69
M,45,15,43
N,49,63,82
O,57,44,12
P,59,8,38
Q,40,68,3
R,78,18,75
S,79,47,21
T,19,45,79
U,84,5,30
V,67,80,64
W,87,22,11
X,11,51,68
Y,88,25,33
Z,31,60,22

字段分别对应姓名，语文成绩，数学成绩，英语成绩

• 需求
  统计各科及格与不及格的人数，按总成绩降序排序

代码实现

自定义Student类

自定义对象来存储数据

import org.apache.hadoop.io.WritableComparable;

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

public class Student implements WritableComparable<Student> {
    private String name;
    private int chinese;
    private int math;
    private int english;
    private int sum;

    public int compareTo(Student o) {
        if (o.sum - this.sum == 0) {
            return o.chinese - this.chinese;
        }
        return o.sum - this.sum;
    }

    public void write(DataOutput dataOutput) throws IOException {
        dataOutput.writeUTF(name);
        dataOutput.writeInt(chinese);
        dataOutput.writeInt(math);
        dataOutput.writeInt(english);
        dataOutput.writeInt(sum);
    }

    public void readFields(DataInput dataInput) throws IOException {
        name = dataInput.readUTF();
        chinese = dataInput.readInt();
        math = dataInput.readInt();
        english = dataInput.readInt();
        sum = dataInput.readInt();
    }

    public void set(String name, int chinese, int math, int english) {
        this.name = name;
        this.chinese = chinese;
        this.math = math;
        this.english = english;
        this.sum = chinese+math+english;
    }

    @Override
    public String toString() {
        return name+"\t"+chinese+"\t"+math+"\t"+english+"\t"+sum;
    }

    public String getName() {
        return name;
    }

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

    public int getChinese() {
        return chinese;
    }

    public void setChinese(int chinese) {
        this.chinese = chinese;
    }

    public int getMath() {
        return math;
    }

    public void setMath(int math) {
        this.math = math;
    }

    public int getEnglish() {
        return english;
    }

    public void setEnglish(int english) {
        this.english = english;
    }

    public int getSum() {
        return sum;
    }

    public void setSum(int sum) {
        this.sum = sum;
    }
}

编写Map类

import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import java.io.IOException;

public class MapTest extends Mapper<LongWritable, Text,Student, NullWritable> {
    Student k = new Student();
    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        String datas [] = value.toString().split(",");
        if (Integer.parseInt(datas[1])>=60){
            context.getCounter("等第","语文及格").increment(1);
        }else {
            context.getCounter("等第","语文不及格").increment(1);
        }
        if (Integer.parseInt(datas[2])>=60){
            context.getCounter("等第","数学及格").increment(1);
        }else {
            context.getCounter("等第","数学不及格").increment(1);
        }
        if (Integer.parseInt(datas[3])>=60){
            context.getCounter("等第","英语及格").increment(1);
        }else {
            context.getCounter("等第","英语不及格").increment(1);
        }
        k.set(datas[0],Integer.parseInt(datas[1]),Integer.parseInt(datas[2]),Integer.parseInt(datas[3]));
        context.write(k,NullWritable.get());
    }
}

编写DriTest

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.File;

public class DriTest {
    public static void main(String[] args) throws Exception {
        File file = new File("D:\\MP\\counter\\output");
        if (file.exists()) {
            delFile(file);
            driver();
        } else {
            driver();
        }
    }

    public static void delFile(File file) {
        File[] files = file.listFiles();
        if (files != null && files.length != 0) {
            for (int i = 0; i < files.length; i++) {
                delFile(files[i]);
            }
        }
        file.delete();
    }

    public static void driver() throws Exception {
        Configuration conf = new Configuration();
        Job job = Job.getInstance(conf);

        job.setMapperClass(MapTest.class);
        job.setJarByClass(DriTest.class);
        //job.setReducerClass(RedTest.class);

        job.setMapOutputKeyClass(Student.class);
        job.setMapOutputValueClass(NullWritable.class);
        // job.setOutputKeyClass(Student.class);
        // job.setOutputValueClass(NullWritable.class);

        FileInputFormat.setInputPaths(job, "D:\\MP\\counter\\input");
        FileOutputFormat.setOutputPath(job, new Path("D:\\MP\\counter\\output"));
        boolean b = job.waitForCompletion(true);
        System.exit(b ? 0 : 1);
    }

结果