利用Key的排序进行二次排序

业务描述：商品价格和订单号进行排序，获取最大的商品价格

第一步：job的描述

public class OrderDriver {

public static void main(String[] args) throws Exception {
// 1 获取配置信息
Configuration conf = new Configuration();
Job job = Job.getInstance(conf);

// 2 设置jar包加载路径
job.setJarByClass(OrderDriver.class);

// 3 加载map/reduce类
job.setMapperClass(OrderMapper.class);
job.setReducerClass(OrderReducer.class);

// 4 设置map输出数据key和value类型
job.setMapOutputKeyClass(OrderBean.class);
job.setMapOutputValueClass(NullWritable.class);

// 5 设置最终输出数据的key和value类型
job.setOutputKeyClass(OrderBean.class);
job.setOutputValueClass(NullWritable.class);

// 6 设置输入数据和输出数据路径
FileInputFormat.setInputPaths(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));

// // 10 设置reduce端的分组
// job.setGroupingComparatorClass(OrderSortGroupingComparator.class);
//
// 10 关联groupingComparator
job.setGroupingComparatorClass(OrderGroupingCompartor.class);
// 7 设置分区
job.setPartitionerClass(OrderPatitioner.class);

// 8 设置reduce个数
job.setNumReduceTasks(3);

// 9 提交
boolean result = job.waitForCompletion(true);
System.exit(result ? 0 : 1);

}
}

第二步：Comparable比较器的实现，这个Bean就是key

public class OrderBean implements WritableComparable<OrderBean> {

private String orderId; // 订单id
private Double price; // 商品价格

public OrderBean() {
super();
}

public OrderBean(String orderId, Double price) {
super();
this.orderId = orderId;
this.price = price;
}

public String getOrderId() {
return orderId;
}

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

public Double getPrice() {
return price;
}

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

@Override
public void write(DataOutput out) throws IOException {
out.writeUTF(orderId);
out.writeDouble(price);
}
@Override
public void readFields(DataInput in) throws IOException {
this.orderId = in.readUTF();
this.price = in.readDouble();

}

@Override
public int compareTo(OrderBean o) {
// 两次排序
// 1 按照id号排序
int comResult = this.orderId.compareTo(o.getOrderId());
if (comResult == 0) {
// 2 按照价格倒序排序
comResult = this.price > o.getPrice()?-1:1;
}
return comResult;
}

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

第三步：分组对比器的实现

public class OrderGroupingCompartor extends WritableComparator {

// 写一个空参构造
public OrderGroupingCompartor(){
super(OrderBean.class, true);
}
// 重写比较的方法
@Override
public int compare(WritableComparable a, WritableComparable b) {
OrderBean aBean = (OrderBean) a;
OrderBean bBean = (OrderBean) b;

// 根据订单id号比较，判断是否是一组
return aBean.getOrderId().compareTo(bBean.getOrderId());
}
}

第四部：分区的实现，目的是含有相同客户ID的orderDean能排在一个区中，（自定义分区）

public class OrderPatitioner extends Partitioner<OrderBean, NullWritable>{

@Override
public int getPartition(OrderBean key, NullWritable value, int numPartitions) {
// 按照key的orderid的hashCode值分区
return (key.getOrderId().hashCode() & Integer.MAX_VALUE) % numPartitions;
}
}

第五步：mapper的实现

public class OrderMapper extends Mapper<LongWritable, Text, OrderBean, NullWritable>{
OrderBean bean = new OrderBean();
@Override
protected void map(LongWritable key, Text value,
Context context) throws IOException, InterruptedException {
// 1 读取数据
String line = value.toString();
// 2 切割数据
String[] fields = line.split("\t");
// Order_0000002 Pdt_03 522.8
// 3 封装bean对象
bean.setOrderId(fields[0]);
bean.setPrice(Double.parseDouble(fields[2]));
// 4 写出
context.write(bean, NullWritable.get());
}

}

第五部：对已排好序的数据取最大或者最小值

public class OrderReducer extends Reducer<OrderBean, NullWritable, OrderBean, NullWritable>{

@Override
protected void reduce(OrderBean bean, Iterable<NullWritable> values,
Context context) throws IOException, InterruptedException {

for(NullWritable v : values){
//System.out.println(key.id+ " : " + key);
}

// 写出
context.write(bean, NullWritable.get());
}
}