Hadoop MapReduce自定义数据类型

一 自定义数据类型的实现

1.继承接口Writable,实现其方法write()和readFields(), 以便该数据能被序列化后完成网络传输或文件输入/输出；

2.如果该数据需要作为主键key使用，或需要比较数值大小时，则需要实现WritalbeComparable接口,实现其方法write(),readFields(),CompareTo() 。

3.重写toString()、hashCode()、equals()方法。 

二 自定义数据类型示例

OrderWritable — 作为key

UserWritable  — 作为value

package com.ibeifeng.mapreduce.io;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.WritableComparable;

public class OrderWritable implements WritableComparable<OrderWritable> {

    private String orderId;
    private float price;

    public OrderWritable() {

    }

    public OrderWritable(String orderId, float price) {
        this.set(orderId, price);
    }

    public void set(String orderId, float price) {
        this.orderId = orderId;
        this.price = price;
    }

    public String getOrderId() {
        return orderId;
    }

    public void setOrderId(String orderId) {
        this.orderId = orderId;
    }

    public float getPrice() {
        return price;
    }

    public void setPrice(float price) {
        this.price = price;
    }

    public void write(DataOutput out) throws IOException {
        out.writeUTF(orderId);
        out.writeFloat(price);

    }

    public void readFields(DataInput in) throws IOException {

        this.orderId = in.readUTF();
        this.price = in.readFloat();
    }

    public int compareTo(OrderWritable o) {

        int comp = this.getOrderId().compareTo(o.getOrderId());

        if (0 == comp) {
            return Float.valueOf(this.getPrice()).compareTo(
                    Float.valueOf(o.getPrice()));
        }

        return comp;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((orderId == null) ? 0 : orderId.hashCode());
        result = prime * result + Float.floatToIntBits(price);
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        OrderWritable other = (OrderWritable) obj;
        if (orderId == null) {
            if (other.orderId != null)
                return false;
        } else if (!orderId.equals(other.orderId))
            return false;
        if (Float.floatToIntBits(price) != Float.floatToIntBits(other.price))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return orderId + "\t" + price;
    }

}

package com.ibeifeng.mapreduce.io;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import org.apache.hadoop.io.Writable;

public class UserWritable implements Writable {

    private int id;
    private String name;

    public UserWritable() {

    }

    public UserWritable(int id, String name) {
        this.set(id, name);
    }

    public void set(int id, String name) {

        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void write(DataOutput out) throws IOException {
        out.writeInt(id);
        out.writeUTF(name);

    }

    public void readFields(DataInput in) throws IOException {
        this.id = in.readInt();
        this.name = in.readUTF();
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + id;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @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 (id != other.id)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return id + "\t" + name;
    }

}