Hadoop中的一些自定義

1. 自定義計數器

   計數器用來監控，hadoop中job的運行進度和狀態。

   如源文件內容爲：

   a    b

   c    d    e    f

   g    h    i

   如今須要找出字段數大於3和小於3的記錄條數，能夠使用計數器來實現，代碼以下：

     public void map(LongWritable key, Text value,

     OutputCollector<Text, Text> output, Reporter reporter)

     throws IOException {

     String[] split = value.toString().split("\t");

     if(split.length>3){

     org.apache.hadoop.mapred.Counters.Counter counter = reporter.getCounter("MyCounter", "isLong");

     counter.increment(1);

     }else if(split.length<3){

     org.apache.hadoop.mapred.Counters.Counter counter = reporter.getCounter("MyCounter","isShort");

     counter.increment(1);

     }

2.  hadoop中的自定義數據類型

    hadoop中默認的數據類型有：

• BooleanWritable:標準布爾型數值

• ByteWritable:單字節數值

• DoubleWritable:雙字節數值

• FloatWritable:浮點數

• IntWritable:整型數

• LongWritable:長整型數

• Text:使用UTF8格式存儲的文本

• NullWritable:當<key, value>中的key或value爲空時使用

    自定義數據類型的實現：

    1.實現Writable接口，並重寫內部write()和readFields()方法，從而完成序列化以後的網絡傳輸和文件輸入或輸出。

    2.若是該數據類型被做爲mapreduce中的key，則該key須要爲可比較的，須要實現WriableComparable接口，並重寫內部write()和readFields()、compare()方法。

    

    代碼以下：

    代碼一：

    

public class Person implements Writable{

long id;

String name;

long age;

@Override

public void readFields(DataInput in) throws IOException {

this.id = in.readLong();

this.name = in.readUTF();

this.age = in.readLong();

}

@Override

public void write(DataOutput out) throws IOException {

out.writeLong(id);

out.writeUTF(name);

out.writeLong(age);

}

        

        @Override

public String toString() {

return "id:"+id+" name:"+name+" age:"+age;

}

public long getId() {

return id;

}

public String getName() {

return name;

}

public long getAge() {

return age;

}

}

    代碼二：基於key的比較

    

package cn.com.bonc.hadoop;

import java.io.DataInput;

import java.io.DataOutput;

import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;

public class PersonSortByAge implements WritableComparable<PersonSortByAge>{

long id;

String name;

long age;

@Override

public void readFields(DataInput in) throws IOException {

in.readLong();

in.readUTF();

in.readLong();

}

@Override

public void write(DataOutput out) throws IOException {

out.writeLong(id);

out.writeUTF(name);

out.writeLong(age);

}

@Override

public int compareTo(PersonSortByAge o) {

return (int) (this.id - o.id);

}

@Override

public String toString() {

return "id:"+id+" name:"+name+" age:"+age;

}

}