一. Hadoop內置的數據類型
- BooleanWritable:標准布爾型數值
- 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為空時使用
二. 用戶自定義數據類型的實現
1.繼承接口Writable,實現其方法write()和readFields(), 以便該數據能被序列化后完成網絡傳輸或文件輸入/輸出；
2.如果該數據需要作為主鍵key使用，或需要比較數值大小時，則需要實現WritalbeComparable接口,實現其方法write(),readFields(),CompareTo() 。
public class Point3D implements Writable<Point3D>
{
private float x,y,z;
public float getX(){return x;}
public float getY(){return y;}
public float getZ(){return z;}
public void readFields(DataInput in) throws IOException
{
x = in.readFloat();
y = in.readFloat();
z = in.readFloat();
}
public void write(DataOutput out) throws IOException
{
out.writeFloat(x);
out.writeFloat(y);
out.writeFloat(z);
}
}
public class Point3D implements WritableComparable<Point3D>
{
private float x,y,z;
public float getX(){return x;}
public float getY(){return y;}
public float getZ(){return z;}
public void readFields(DataInput in) throws IOException
{
x = in.readFloat();
y = in.readFloat();
z = in.readFloat();
}
public void write(DataOutput out) throws IOException
{
out.writeFloat(x);
out.writeFloat(y);
out.writeFloat(z);
}
public int CompareTo(Point3D p)
{
//具體實現比較當前的空間坐標點this(x,y,z)與指定的點p(x,y,z)的大小
// 並輸出： -1(小於), 0(等於), 1(大於)
}
}