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;

     }

 }

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