数据类型(都实现了Writable接口)
BooleanWritable布尔类型
ByteWritable单字节数值
DoubleWritable双字节数值
FloatWritable浮点数
IntWritable整型数
LongWritable长整型
TextUTF-8格式存储的文本
NullWritable空类型
因为shuffle中排序依据是key,若定义的数据类型为Key,必须实现writable和comparable接口，即WritableComparable接口
Writable
write()把每个对象序列化到输出流
readFilds()把输入流字节反序列化到输入流
自定义数据类型实例
1.定义私有变量
2.setter，getter方法
3.无参有参构造器
4.set()方法，帮助构造器初始化数据（Hadoop偏爱）
5.hashCode()方法和equals()方法
6.toString()方法
7.implement Writable并实现write()方法readFilds()方法
8.implement WritableComparable并实现compareTo()方法
package com.cenzhongman.io;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;public class UserWritable implements WritableComparable<UserWritable> {
private int ip;
private String name;public UserWritable() {
}public UserWritable(int ip, String name) {
this.set(ip, name);
}@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + ip;
result = prime * result + ((name == null) ? 0 : name.hashCode());
return result;
}@Override
public String toString() {
return ip + "\t" + name;
}@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
UserWritable other = (UserWritable) obj;
if (ip != other.ip)
return false;
if (name == null) {
if (other.name != null)
return false;
} else if (!name.equals(other.name))
return false;
return true;
}public void set(int ip, String name) {
this.setIp(ip);
this.setName(name);
}public int getIp() {
return ip;
}public void setIp(int ip) {
this.ip = ip;
}public String getName() {
return name;
}public void setName(String name) {
this.name = name;
}// read和write方法元素的顺序必须一致
@Override
public void readFields(DataInput arg0) throws IOException {
this.ip = arg0.readInt();
this.name = arg0.readUTF();
}@Override
public void write(DataOutput arg0) throws IOException {
arg0.writeInt(ip);
arg0.writeUTF(name);
}@Override
public int compareTo(UserWritable o) {
int comp = Integer.valueOf(this.getIp()).compareTo(o.getIp());if (comp != 0) {
return comp;
}
return this.getName().compareTo(o.getName());
}
}
