自定义MapReduce的类型

package org.apache.hadoop.mapreduce.io;

import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;

import org.apache.hadoop.io.WritableComparable;

/***
 * customize writable eg.order
 *
 * @author nele
 *
 */
public class OrderWritable implements WritableComparable<OrderWritable> {

    private String orderId;

    private float price;

    public OrderWritable() {
    }

    public OrderWritable(String orderId, float price) {
        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.orderId.compareTo(o.orderId);
        if (comp == 0) {
                return Float.valueOf(this.price).compareTo(Float.valueOf(o.price));
        }
        return comp;
    }

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

    @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;
    }

}

这样就可以，在mapreduce中使用。

需要根据具体的情境具体的设计。