Hadoop序列化机制

1.实现Writable接口

2.如果要进行排序，根据Comparable接口的compareTo方法，但是单独实现Comparable接口会报异常，我们需要实现hadoop提供的WritableComparable接口，不能这么实现:Writable,Comparable

package cn.itheima.bigdata.hadoop.flow;

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

import org.apache.hadoop.io.Writable;
import org.apache.hadoop.io.WritableComparable;

/**
 * 在hadoop中，自定义的bean如果需要进行网络传输，必须实现hadoop的序列化框架，就是实现接口Writable
 * hadoop自带的序列化机制相比Serializable来说，传输的信息更加精简
 * 在hadoop项目的规划中，以后的序列化机制可能采用Avro框架（可以跨语言）
 * @author duanhaitao@itcast.cn
 *
 */

// WritableComparable<T> extends Writable, Comparable<T>
//但是在我们的自定义bean里面不能自己写成implements Writable,Comparable<T>,会报异常
public class FlowBean implements WritableComparable<FlowBean>{
 
 private String phoneNbr;
 private long up_flow;
 private long d_flow;
 private long sum_flow;
 
 
 //因为这个bean在反序列化时需要被反射出实例，就需要一个无参构造函数
 public FlowBean(){}
 
 public FlowBean(long up_flow,long d_flow){
  this.up_flow = up_flow;
  this.d_flow = d_flow;
  this.sum_flow = up_flow + d_flow;
 }
 
 
 public void set(String phoneNbr,long up_flow,long d_flow){
  this.phoneNbr = phoneNbr;
  this.up_flow = up_flow;
  this.d_flow = d_flow;
  this.sum_flow = up_flow + d_flow;
 }
 
 
 
 public long getUp_flow() {
  return up_flow;
 }
 public void setUp_flow(long up_flow) {
  this.up_flow = up_flow;
 }
 public long getD_flow() {
  return d_flow;
 }
 public void setD_flow(long d_flow) {
  this.d_flow = d_flow;
 }
 public long getSum_flow() {
  return sum_flow;
 }
 public void setSum_flow(long sum_flow) {
  this.sum_flow = sum_flow;
 }

 
 public String getPhoneNbr() {
  return phoneNbr;
 }

 public void setPhoneNbr(String phoneNbr) {
  this.phoneNbr = phoneNbr;
 }

 /**
  * 将对象中的信息序列化写入输出流
  */
 @Override
 public void write(DataOutput out) throws IOException {
  
  out.writeUTF(phoneNbr);
  out.writeLong(up_flow);
  out.writeLong(d_flow);
  out.writeLong(sum_flow);
  
 }

 /**
  * 从数据流中反序列化出各个字段，读的顺序要与序列化时写入的顺序一致
  */
 @Override
 public void readFields(DataInput in) throws IOException {

  phoneNbr = in.readUTF();
  up_flow = in.readLong();
  d_flow = in.readLong();
  sum_flow = in.readLong();
  
 }
 
 @Override
 public String toString() {
  
  return up_flow + "\t" + d_flow + "\t" + sum_flow;
 }

 @Override
 public int compareTo(FlowBean o) {
  
  return this.sum_flow > o.getSum_flow()?-1:1;
 }
 
 
}