hadoop 序列化自定数据数据对象

自定义数据对象 calss Point implements Writable {     int x;     int y;     @Override     public void readFields(DataInput in) throws IOException {         // TODO Auto-generated method stub        x=in.readInt();        y=in.readInt();     }     @Override     public void write(DataOutput out) throws IOException {         // TODO Auto-generated method stub         out.writeInt(x);         out.writeFloat(y);     } } 再自定义一个嵌套前一个对象，数据对象 class PointSet implements Writable {     ArrayList points=new ArrayList();     Point point;     @Override     public void readFields(DataInput in) throws IOException {         // TODO Auto-generated method stub      ??如何序列化？？     }     @Override     public void write(DataOutput out) throws IOException {         // TODO Auto-generated method stub    ？？如何学列化？？？     } } 请大神，指点下，PointSet对象如何进行序列化？？？急，在线等。