Hadoop中的一些自定义

1. 自定义计数器

   计数器用来监控，hadoop中job的运行进度和状态。

   如源文件内容为：

   a    b

   c    d    e    f

   g    h    i

   如今须要找出字段数大于3和小于3的记录条数，能够使用计数器来实现，代码以下：

     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中的自定义数据类型

    hadoop中默认的数据类型有：

• BooleanWritable:标准布尔型数值

• ByteWritable:单字节数值

• DoubleWritable:双字节数值

• FloatWritable:浮点数

• IntWritable:整型数

• LongWritable:长整型数

• Text:使用UTF8格式存储的文本

• NullWritable:当<key, value>中的key或value为空时使用

    自定义数据类型的实现：

    1.实现Writable接口，并重写内部write()和readFields()方法，从而完成序列化以后的网络传输和文件输入或输出。

    2.若是该数据类型被做为mapreduce中的key，则该key须要为可比较的，须要实现WriableComparable接口，并重写内部write()和readFields()、compare()方法。

    

    代码以下：

    代码一：

    

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;

}

}

    代码二：基于key的比较

    

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;

}

}