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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 {

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 {

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;

}

}

感谢各位的阅读，以上就是"Hadoop怎么自定制数据类型"的内容了，经过本文的学习后，相信大家对Hadoop怎么自定制数据类型这一问题有了更深刻的体会，具体使用情况还需要大家实践验证。这里是，小编将为大家推送更多相关知识点的文章，欢迎关注!

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