Hadoop怎么自定制数据类型

蜗牛互联网技术资讯2021-12-093210

这篇文章主要讲解了“Hadoop怎么自定制数据类型”，文中的讲解内容简单清晰，易于学习与理解，下面请大家跟着小编的思路慢慢深入，一起来研究和学习“Hadoop怎么自定制数据类型”吧！

一般有两个办法，一种较为简单的是针对值，另外一种更为完整的是对于键和值都适应的方法：
1、实现Writable接口：

/* DataInput and DataOutput 类是java.io的类 */
public interface Writable {
void readFields(DataInput in);
void write(DataOutput out);
}

下面是一个小例子：
public class Point3D implement Writable {
public float x, y, z;
public Point3D(float fx, float fy, float fz) {
  this.x = fx;
  this.y = fy;
  this.z = fz;
}
public Point3D() {
  this(0.0f, 0.0f, 0.0f);
}
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 String toString() {
  return Float.toString(x) + ", "
   + Float.toString(y) + ", "
   + Float.toString(z);
}
}

2、对于键来说，需要指定排序规则，对此，Java版Hadoop的办法是实现WritableComparable这个泛型接口，WritableComparable，顾名思义了，一半是Writable，一半是Comparable

public interface WritableComparable<T> {
public void readFields(DataInput in);
public void write(DataOutput out);
public int compareTo(T other);
}

这里的compareTo方法是默认的key排序

先给出下面的简单例子，再做说明和扩展。
public class Point3D inplements WritableComparable {
public float x, y, z;
public Point3D(float fx, float fy, float fz) {
  this.x = fx;
  this.y = fy;
  this.z = fz;
}
public Point3D() {
  this(0.0f, 0.0f, 0.0f);
}
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 String toString() {
  return Float.toString(x) + ", "
   + Float.toString(y) + ", "
   + Float.toString(z);
}
public float distanceFromOrigin() {
  return (float) Math.sqrt( x*x + y*y +z*z);
}
public int compareTo(Point3D other) {
  return Float.compareTo(
   distanceFromOrigin(),
   other.distanceFromOrigin());
}
public boolean equals(Object o) {
  if( !(o instanceof Point3D)) {
   return false;
  }
  Point3D other = (Point3D) o;
  return this.x == o.x
   && this.y == o.y
   && this.z == o.z;
}
/* 实现 hashCode() 方法很重要
* Hadoop的Partitioners会用到这个方法，后面再说
*/
public int hashCode() {
  return Float.floatToIntBits(x)
   ^ Float.floatToIntBits(y)
   ^ Float.floatToIntBits(z);
}
}
如果要将对象写入数据库则还要继承DBWritable接口

public interface WritableComparable<T> {
public void write(PreparedStatement statement) throwsSQLException;
public void readFields(ResultSet resultSet) throws SQLException;}

下面写个例子

public class LocationBean implements Writable, DBWritable {
    private String mobilenetworkcode;

    private String mobilecountrycode;

    private Integer cellid;

    private Integer locationareacode;

    private Integer baiduareaid;

    private Double lat;

    private Double lng;

    private Integer areaid;
    @Override
    public void write(PreparedStatement statement) throws SQLException {
        int index = 1;
        statement.setString(index++, this.getMobilenetworkcode());
        statement.setString(index++, this.getMobilecountrycode());
        statement.setInt(index++, this.getCellid());
        statement.setInt(index++, this.getLocationareacode());
        statement.setInt(index++, this.getBaiduareaid());
        statement.setDouble(index++, this.getLat());
        statement.setDouble(index++, this.getLng());
        statement.setInt(index, this.getAreaid());
    }

    @Override
    public void readFields(ResultSet resultSet) throws SQLException {
         this.mobilenetworkcode = resultSet.getString(1);
         this.mobilecountrycode = resultSet.getString(2);
         this.cellid = resultSet.getInt(3);
         this.locationareacode = resultSet.getInt(4);
         this.baiduareaid = resultSet.getInt(5);
         this.lat = resultSet.getDouble(6);
         this.lng = resultSet.getDouble(7);
         this.areaid = resultSet.getInt(8);
    }

    @Override
    public void write(DataOutput out) throws IOException {
        // TODO Auto-generated method stub

    }

    @Override
    public void readFields(DataInput in) throws IOException {


    }

    public String getMobilenetworkcode() {
        return mobilenetworkcode;
    }

    public void setMobilenetworkcode(String mobilenetworkcode) {
        this.mobilenetworkcode = mobilenetworkcode;
    }

    public String getMobilecountrycode() {
        return mobilecountrycode;
    }

    public void setMobilecountrycode(String mobilecountrycode) {
        this.mobilecountrycode = mobilecountrycode;
    }

    public Integer getCellid() {
        return cellid;
    }

    public void setCellid(Integer cellid) {
        this.cellid = cellid;
    }

    public Integer getLocationareacode() {
        return locationareacode;
    }

    public void setLocationareacode(Integer locationareacode) {
        this.locationareacode = locationareacode;
    }

    public Integer getBaiduareaid() {
        return baiduareaid;
    }

    public void setBaiduareaid(Integer baiduareaid) {
        this.baiduareaid = baiduareaid;
    }

    public Double getLat() {
        return lat;
    }

    public void setLat(Double lat) {
        this.lat = lat;
    }

    public Double getLng() {
        return lng;
    }

    public void setLng(Double lng) {
        this.lng = lng;
    }

    public Integer getAreaid() {
        return areaid;
    }

    public void setAreaid(Integer areaid) {
        this.areaid = areaid;
    }

}