hadoop中的输入输出数据类型：
BooleanWritable:标准布尔型数值
ByteWritable:单字节数值
DoubleWritable:双字节数值
FloatWritable:浮点数
常用的：
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
hadoop中的数据类型都实现了writable接口，以便这些类型的数据可以在网络传输和文件存储
自定义数据类型：
①实现WritableComparable接口，实现write和readFields方法，完成可序列化和反序列化
②如果该数据类型需要有比较顺序时，实现CompareTo（）方法
③必须声明一个无参构造方法，为了方便反射，创建对象
package com.neworigin.temperature;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;
public class Weather implements WritableComparable <Weather> {
private int year;
private int month;
private int day;
private int wd;
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public int getMonth() {
return month;
}
public void setMonth(int month) {
this.month = month;
}
public int getDay() {
return day;
}
public void setDay(int day) {
this.day = day;
}
public int getWd() {
return wd;
}
public void setWd(int wd) {
this.wd = wd;
}
public void write(DataOutput out) throws IOException {
out.writeInt(year);
out.writeInt(month);
out.writeInt(day);
out.writeInt(wd);
}
public void readFields(DataInput in) throws IOException {
year=in.readInt();
month=in.readInt();
day=in.readInt();
wd=in.readInt();
}
//将年月日按升序排序
public int compareTo(Weather w) {
int c1 = Integer.compare(this.year,w.getYear());
if (c1==0)
{
int c2 = Integer.compare(this.month,w.getMonth());
if (c2==0)
{
return Integer.compare(this.wd,w.getWd());
}
return c2;
}
return c1;
}
}