Left join --案例1

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统计xx订单个数和价格总和：

package com.testMr;import java.io.IOException;import java.util.ArrayList;import java.util.Iterator;import java.util.LinkedList;import java.util.List;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;import org.apache.hadoop.io.Text;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.Reducer;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.input.FileSplit;import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;import org.apache.hadoop.mapreduce.lib.partition.HashPartitioner;public class LeftJoinDemo {public static class LeftJoinMap extends Mapper<LongWritable, Text, Text, Text> {@Overrideprotected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, Text>.Context context)throws IOException, InterruptedException {String[] arr = value.toString().split(" ");FileSplit file = (FileSplit) context.getInputSplit();String path = file.getPath().toString();String buyer;if (path.contains("trade.txt")) {buyer = arr[2];context.write(new Text(buyer), new Text(value.toString() + " " + "a"));} else {buyer = arr[1];context.write(new Text(buyer), new Text(value.toString() + " " + "b"));}}}public static class LeftJoinReduce extends Reducer<Text, Text, Text, Text> {@Overrideprotected void reduce(Text arg0, Iterable<Text> arg1, Reducer<Text, Text, Text, Text>.Context arg2)throws IOException, InterruptedException {List<String> a = new ArrayList<String>();List<String> b = new ArrayList<String>();String[] arr;List<String> list = new LinkedList<String>();

                        // 这个变量用来存放确认是北京的订单id，因为在order里没有城市列，所以在划分trade时，把是北京的id，记一下for (Text line : arg1) {arr = line.toString().split(" ");if (arr[arr.length - 1].equals("a") && arr[3].equals("北京")) {a.add(line.toString());list.add(arr[0]);} else {b.add(line.toString());}}int tradesize = a.size(); // 订单个数int priceSum = 0; // 价格总和String price;for (String order : b) {arr = order.split(" ");if (list.contains(arr[0])) {

                        // 查看这个order的id是不是在北京id的list里，是的话累加price = arr[3];priceSum += Integer.parseInt(price);}}arg2.write(arg0, new Text(tradesize + " " + priceSum)); }}public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {System.out.println(args.length);for (String str : args) {System.out.println(str);}String input1 = args[0];String input2 = args[1];String outputPath = args[2];Job job = Job.getInstance();job.setJobName("test");job.setJarByClass(LeftJoinDemo.class);FileInputFormat.addInputPath(job, new Path(input1));FileInputFormat.addInputPath(job, new Path(input2));FileOutputFormat.setOutputPath(job, new Path(outputPath));job.setMapperClass(LeftJoinMap.class);job.setReducerClass(LeftJoinReduce.class);job.setPartitionerClass(HashPartitioner.class);job.setNumReduceTasks(1);job.setOutputValueClass(Text.class);job.setOutputKeyClass(Text.class);System.exit(job.waitForCompletion(true) ? 0 : 1);}}

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