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;
     }

 }