文章标题 Hadoop:编写一个求和排序的MR

    搞Hadoop开发，尤其是编写MR程序：总是难免遇到许多奇奇怪怪的问题，第一次编写一个排序求和的MR程序时就是如此。一；遇到的第一个问题：16/01/10 15:40:19 WARN mapred.LocalJobRunner: job_local2074055527_0001

java.lang.Exception: java.lang.RuntimeException: java.lang.NoSuchMethodException: Hadoop.Hu.Maprduce.sort.SumStepSumMapper.()atorg.apache.hadoop.mapred.LocalJobRunnerJob.run(LocalJobRunner.java:403)
Caused by: java.lang.RuntimeException: java.lang.NoSuchMethodException: Hadoop.Hu.Maprduce.sort.SumStep$SumMapper.()
at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:131)
at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:721)
at org.apache.hadoop.mapred.MapTask.run(MapTask.java:339)
出现这种情况的原因是：1自己的编写的序列化类中，如果有有参构造函数，必须写无参构造函数，但事实上我是用的void set()方法。并不需要写无参构造函数
2，后现是自己太大意了，在Mapper和Reduceer方法中没有加static，修改后继续运行
二，又出来错误，显示数组越界，奇异值以为是自己参数弄错了，导致数组越界，后来就远程debug，检查来检查去都感觉不是代码错误，后来在群里求救，然后冷静下来是自己的数据有错，所以要随时注意光标的位置！最后把自己的怠代码拿出来！
Java.io.IOException;

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.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class SumStep {

public  class SumMapper extends Mapper<LongWritable, Text, Text, InfoBean>{    private InfoBean v = new InfoBean();    private Text k = new Text();    @Override    protected void map(LongWritable key, Text value, Context context)            throws IOException, InterruptedException {        String line = value.toString();        String[] fileds = line.split("\t");        String account = fileds[0];        double in = Double.parseDouble(fileds[1]);        double out = Double.parseDouble(fileds[2]);        k.set(account);        v.set(account, in, out);        context.write(k, v);            }}public  class SumReducer extends Reducer<Text, InfoBean, Text, InfoBean>{    private InfoBean v = new InfoBean();    @Override    protected void reduce(Text key, Iterable<InfoBean> v2s, Context context)            throws IOException, InterruptedException {        double in_sum = 0;        double out_sum = 0;        for( InfoBean bean : v2s){            in_sum += bean.getIncome();            out_sum += bean.getExpenses();        }        v.set("",in_sum,out_sum);        context.write(key, v);    }}public static void main(String[] args) throws Exception {    Configuration conf = new Configuration();    Job job = Job.getInstance(conf);    job.setJarByClass(SumStep.class);    job.setMapperClass(SumMapper.class);    job.setMapOutputKeyClass(Text.class);    job.setMapOutputValueClass(InfoBean.class);    FileInputFormat.setInputPaths(job, new Path(args[0]));    job.setReducerClass(SumReducer.class);    job.setOutputKeyClass(Text.class);    job.setOutputValueClass(InfoBean.class);    FileOutputFormat.setOutputPath(job,new Path(args[1]));    job.waitForCompletion(true);    }

}
写代码片`
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;

public class InfoBean implements WritableComparable {
private String account;
private double income;
private double expenses;
private double surplus;

public void set(String account,double income,double expenses ){     this.account = account;    this.income = income;    this.expenses = expenses;    this.surplus = income - expenses;}@Overridepublic String toString() {    return this.income+ "\t" +this.expenses+ "\t" +this.surplus;}@Overridepublic void write(DataOutput out) throws IOException {    out.writeUTF(account);    out.writeDouble(income);    out.writeDouble(expenses);    out.writeDouble(surplus);   }@Overridepublic void readFields(DataInput in) throws IOException {                this.account =in.readUTF();                this.income = in.readDouble();                this.expenses = in.readDouble();                this.surplus = in.readDouble();                                     }@Overridepublic int compareTo(InfoBean o) {    if(this.income == o.getIncome()){        return this.expenses > o.getExpenses() ? 1 : -1;    }    else{        return this.income > o.getIncome() ? -1 : 1;    }   }public String getAccount() {    return account;}public void setAccount(String account) {    this.account = account;}public double getIncome() {    return income;}public void setIncome(double income) {    this.income = income;}public double getExpenses() {    return expenses;}public void setExpenses(double expenses) {    this.expenses = expenses;}public double getSurplus() {    return surplus;}public void setSurplus(double surplus) {    this.surplus = surplus;}

}