GroupingComparator分组案例实操
OrderBean
public class OrderBean implements WritableComparable<OrderBean> {
private int order_id; //订单id
private double price; //价格
public OrderBean() {
super();
}
public OrderBean(int order_id, double price) {
super();
this.order_id = order_id;
this.price = price;
}
@Override
public int compareTo(OrderBean bean) {
//先按照id升序排序，如果相同按照价格降序排序
int result;
if (order_id > bean.getOrder_id()) {
result = 1;
} else if (order_id < bean.getOrder_id()) {
result = -1;
} else {
if (price > bean.getPrice()) {
result = -1;
} else if (price < bean.getPrice()) {
result = 1;
} else {
result = 0;
}
}
return result;
}
@Override
public void write(DataOutput out) throws IOException {
out.writeInt(order_id);
out.writeDouble(price);
}
@Override
public void readFields(DataInput in) throws IOException {
order_id = in.readInt();
price = in.readDouble();
}
public int getOrder_id() {
return order_id;
}
public void setOrder_id(int order_id) {
this.order_id = order_id;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
@Override
public String toString() {
return order_id + "\t" + price;
}
}
OrderMapper
public class OrderMapper extends Mapper<LongWritable, Text, OrderBean, NullWritable>{
OrderBean k = new OrderBean();
@Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
// 1 获取一行
String line = value.toString();
// 2 切割
String[] fields = line.split(" ");
// 3 封装对象
k.setOrder_id(Integer.parseInt(fields[0]));
k.setPrice(Double.parseDouble(fields[2]));
// 4 写出
context.write(k, NullWritable.get());
}
}
OrderReducer
public class OrderReducer extends Reducer<OrderBean, NullWritable, OrderBean, NullWritable>{
@Override
protected void reduce(OrderBean key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
context.write(key, NullWritable.get());
}
}
OrderDirver
public class OrderDirver {
public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
//输入输出路径需要根据自己电脑上的实际的输入输出路径设置
args = new String[]{"e:/input/inputorder", "e:/output1"};
// 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(OrderDirver.class);
// 3 加载map/reduce类
job.setMapperClass(OrderMapper.class);
job.setReducerClass(OrderReducer.class);
// 4 设置map输出数据kv类型
job.setMapOutputKeyClass(OrderBean.class);
job.setMapOutputValueClass(NullWritable.class);
// 5 设置最终输出数据的kv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]));
// 8 设置reduce端的分组
job.setGroupingComparatorClass(OrderGroupingComparator.class);
// 7 提交job
boolean result = job.waitForCompletion(true);
System.exit(result ? 0 : 1);
}
}
OrderGroupingComparator
public class OrderGroupingComparator extends WritableComparator {
protected OrderGroupingComparator() {
super(OrderBean.class, true);
}
@Override
public int compare(WritableComparable a, WritableComparable b) {
//要求只要id相同，就认为是相同的key
OrderBean aBean = (OrderBean) a;
OrderBean bBean = (OrderBean) b;
int result;
if (aBean.getOrder_id() > bBean.getOrder_id()) {
result = 1;
} else if (aBean.getOrder_id() < bBean.getOrder_id()) {
result = -1;
} else {
result = 0;
}
return result;
}
}
PS：如果要显示top3可修改Reducer
OrderReducer
public class OrderReducer extends Reducer<OrderBean, NullWritable, OrderBean, NullWritable> {
@Override
protected void reduce(OrderBean key, Iterable<NullWritable> values, Context context) throws IOException, InterruptedException {
//循环的时候设置循环次数为3即可
for (NullWritable nullWritable : values) {
context.write(key, NullWritable.get());
}
}
}
