1、单词计数

在一定程度上反映了MapReduce设计的初衷--对日志文件进行分析。

public class WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable>{//该方法循环调用，从文件的split中读取每行调用一次，把该行所在的下标为key，该行的内容为valueprotected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {String[] words = StringUtils.split(value.toString(), ' ');for(String w :words){context.write(new Text(w), new IntWritable(1));}}
}

public class WordCountReducer extends Reducer<Text, IntWritable, Text, IntWritable>{//每组调用一次，这一组数据特点：key相同，value可能有多个。protected void reduce(Text key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException {int sum =0;for(IntWritable i: values){sum=sum+i.get();}context.write(key, new IntWritable(sum));}
}

public class RunJob {public static void main(String[] args) {Configuration config =new Configuration();
//	config.set("fs.defaultFS", "hdfs://node1:8020");
//	config.set("yarn.resourcemanager.hostname", "node1");
//      config.set("mapred.jar", "C:\\Users\\Administrator\\Desktop\\wc.jar");try {FileSystem fs =FileSystem.get(config);Job job =Job.getInstance(config);job.setJarByClass(RunJob.class);job.setJobName("wc");job.setMapperClass(WordCountMapper.class);job.setReducerClass(WordCountReducer.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(IntWritable.class);FileInputFormat.addInputPath(job, new Path("/usr/input/"));Path outpath =new Path("/usr/output/wc");if(fs.exists(outpath)){fs.delete(outpath, true);}FileOutputFormat.setOutputPath(job, outpath);boolean f= job.waitForCompletion(true);if(f){System.out.println("job completed!");}} catch (Exception e) {e.printStackTrace();}}
}

2、数据去重

最终目标是让原始数据中出现次数超过一次的数据在输出文件中只出现一次。

自然会想到将同一个数据的所有记录都交给一台Reduce机器，无论这个数据出现多少次，只要在最终结果中输出一次就可以了。

将单次计数程序稍加改动即可。

public class DedupMapper extends Mapper<LongWritable, Text, Text, NullWritable>{protected void map(LongWritable key, Text value,Context context) throws IOException, InterruptedException {context.write(key, NullWritable.get());}
}

public class DedupReducer extends Reducer<Text, NullWritable, Text, NullWritable>{protected void reduce(Text key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException {context.write(key, NullWritable.get());}
}

public class RunJob {public static void main(String[] args) {Configuration config =new Configuration();
//	config.set("fs.defaultFS", "hdfs://node1:8020");
//	config.set("yarn.resourcemanager.hostname", "node1");config.set("mapred.jar", "C:\\Users\\Administrator\\Desktop\\wc.jar");try {FileSystem fs =FileSystem.get(config);Job job =Job.getInstance(config);job.setJarByClass(RunJob.class);job.setJobName("dedup");job.setMapperClass(DedupMapper.class);job.setReducerClass(DedupReducer.class);job.setMapOutputKeyClass(Text.class);job.setMapOutputValueClass(NullWritable.class);FileInputFormat.addInputPath(job, new Path("/usr/input/"));Path outpath =new Path("/usr/output/dedup");if(fs.exists(outpath)){fs.delete(outpath, true);}FileOutputFormat.setOutputPath(job, outpath);boolean f= job.waitForCompletion(true);if(f){System.out.println("job completed!");}} catch (Exception e) {e.printStackTrace();}}
}

3、排序

对输入文件中的内容进行排序。

输入文件中的每行内容均为一个数字，即一个数据。

要求在输出中每行有两个间隔的数字，第二个数字代表原始数据，第一个数字代表原始数据的位次。

样例输入：

file1:

654

765

65223

file2:

5956

650

file3:

样例输出：

1 2

2 6

3 15

4 22

5 26

6 32

7 32

8 54

9 92

10 650

11 654

12 756

13 5956

14 65223

设计思路：

可以利用MapReduce过程中默认的排序，而不需要自己再实现排序。

重点：

1、待排序数据作为Map任务的key；

2、需要重写partition类，保证整体有序，具体做法是用输入数据的最大值除以系统partition数量的商作为分割数据的边界，即分割数据的边界为此商的1倍、2倍至numPartitions-1倍，这样就能保证执行完partition后是整体有序的。

3、Reduce获得<key, value-list>，根据value-list中元素的个数将输入的key作为value的输出次数。

package hadoop;import java.io.IOException;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Partitioner;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;public class Sort
{public static class SortMapper extends Mapper<Object, Text, IntWritable, NullWritable>{private NullWritable nw = NullWritable.get();@Overrideprotected void map(Object key, Text value, Mapper<Object, Text, IntWritable, NullWritable>.Context context)throws IOException, InterruptedException{context.write(new IntWritable(Integer.parseInt(value.toString().trim())), nw);}}public static class SortReducer extends Reducer<IntWritable, NullWritable, IntWritable, IntWritable>{private IntWritable counter = new IntWritable(1);@Overrideprotected void reduce(IntWritable key, Iterable<NullWritable> values,Reducer<IntWritable, NullWritable, IntWritable, IntWritable>.Context context)throws IOException, InterruptedException{for(NullWritable nw : values){context.write(counter, key);counter = new IntWritable(counter.get() + 1);}}}public static class SortPartitioner extends Partitioner<IntWritable, NullWritable>{//numPartitions equals with the number of reduce tasks@Overridepublic int getPartition(IntWritable key, NullWritable value, int numPartitions){int maxNumber = 65223;int bound = maxNumber/numPartitions;int keyNumber = key.get();for (int i = 0; i < numPartitions; ++i){if (keyNumber <= (i+1)*bound)return i;}return 0;}}public static void main(String[] args) throws Exception{Configuration conf = new Configuration();Job job = Job.getInstance(conf);job.setJarByClass(Sort.class);job.setJobName("sort");job.setMapperClass(SortMapper.class);job.setReducerClass(SortReducer.class);job.setOutputKeyClass(IntWritable.class);job.setOutputValueClass(IntWritable.class);job.setMapOutputKeyClass(IntWritable.class);job.setMapOutputValueClass(NullWritable.class);job.setNumReduceTasks(5);job.setPartitionerClass(SortPartitioner.class);String inputFile = "/home/jinzhao/dataset/input";String outputFile = "/home/jinzhao/dataset/output";FileInputFormat.setInputPaths(job, new Path(inputFile));Path output = new Path(outputFile);FileSystem fs = FileSystem.get(conf);if (fs.exists(output))fs.delete(output, true);FileOutputFormat.setOutputPath(job, output);job.waitForCompletion(true);}
}

4、单表关联

样例输入：

file:

child parent

Tom Lucy

Tom Jack

Jone Lucy

Jone Jack

Lucy Mary

Lucy Ben

Jack Alice

Jack Jesse

Terry Alice

Terry Jesse

Philip Terry

Philip Alma

Mark Terry

Mark Alma

样例输出：

file:

grandchild grandparent

Tom Alice

Tom Jesse

Jone Alice

Jone Jesse

Tom Mary

Tom Ben

Jone Mary

Jone Ben

Philip Alice

philip Jesse

Mark Alice

Mark Jesse

package hadoop;import java.io.IOException;
import java.util.ArrayList;
import java.util.List;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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.output.FileOutputFormat;public class stlink
{private static boolean flag = true;public static class stlinkMapper extends Mapper<Object, Text, Text, Text>{@Overrideprotected void map(Object key, Text value, Mapper<Object, Text, Text, Text>.Context context)throws IOException, InterruptedException{String[] names = value.toString().trim().split("\t");if (names[0].compareTo("child") != 0){				context.write(new Text(names[0]), new Text("parent:"+names[1]));context.write(new Text(names[1]), new Text("child:"+names[0]));}}}public static class stlinkReducer extends Reducer<Text, Text, Text, Text>{@Overrideprotected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, Text>.Context context)throws IOException, InterruptedException{if (flag){context.write(new Text("grandchild"), new Text("grandparent"));flag = false;}List<String> children = new ArrayList<String>();List<String> parents = new ArrayList<String>();for(Text t : values){String[] kv = t.toString().split(":");if (kv[0].compareTo("child") == 0)children.add(kv[1]);elseparents.add(kv[1]);}for(String c : children)for(String p : parents)context.write(new Text(c), new Text(p));}}public static void main(String[] args) throws Exception{Configuration conf = new Configuration();Job stlinkJob = Job.getInstance(conf);stlinkJob.setJarByClass(stlink.class);stlinkJob.setJobName("single table link");stlinkJob.setMapperClass(stlinkMapper.class);stlinkJob.setReducerClass(stlinkReducer.class);stlinkJob.setOutputKeyClass(Text.class);stlinkJob.setOutputValueClass(Text.class);stlinkJob.setMapOutputKeyClass(Text.class);stlinkJob.setMapOutputValueClass(Text.class);Path input = new Path("/home/jinzhao/dataset/input");Path output = new Path("/home/jinzhao/dataset/output");FileInputFormat.setInputPaths(stlinkJob, input);FileSystem fs = FileSystem.get(conf);if (fs.exists(output))fs.delete(output, true);FileOutputFormat.setOutputPath(stlinkJob, output);stlinkJob.waitForCompletion(true);}
}

5、多表关联

样例输入：

factory:

factoryname addressed

Beijing Red Star 1

Shenzhen Thunder 3

Guangzhou Honda 2

Beijing Rising 1

Guangzhou Development Bank 2

Tencent 3

Bank of Beijing 1

address:

1 Beijing

2 Guangzhou

3 Shenzhen

4 Xian

package hadoop;import java.io.IOException;
import java.util.ArrayList;
import java.util.List;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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.output.FileOutputFormat;public class mtlink
{private static boolean flag = true;public static class mtlinkMapper extends Mapper<Object, Text, Text, Text>{@Overrideprotected void map(Object key, Text value, Mapper<Object, Text, Text, Text>.Context context)throws IOException, InterruptedException{String str = value.toString();if (str.contains("factoryname") || str.contains("addressname"))return;String[] infos = str.trim().split(" ");if (infos[0].charAt(0) >= '0' && infos[0].charAt(0) <= '9')context.write(new Text(infos[0]), new Text("right:" + strCombine(infos, "right")));elsecontext.write(new Text(infos[infos.length - 1]), new Text("left:" + strCombine(infos, "left")));}private String strCombine(String[] strs, String direction){StringBuilder sb = new StringBuilder();if (direction.compareTo("right") == 0)for(int i = 1; i < strs.length; ++i)sb.append(strs[i] + " ");elsefor (int i = 0; i < strs.length - 1; ++i)sb.append(strs[i] + " ");return sb.toString().trim();}}public static class mtlinkReducer extends Reducer<Text, Text, Text, Text>{@Overrideprotected void reduce(Text key, Iterable<Text> values, Reducer<Text, Text, Text, Text>.Context context)throws IOException, InterruptedException{if (flag){context.write(new Text("factoryname"), new Text("adressname"));flag = false;}List<String> companies = new ArrayList<String>();String place = "huoxing";for (Text t : values){String[] kv = t.toString().trim().split(":");if (kv[0].compareTo("right") == 0)place = kv[1];elsecompanies.add(kv[1]);}for (String s : companies)context.write(new Text(s), new Text(place));}}public static void main(String[] args) throws Exception{Configuration conf = new Configuration();Job mtlinkJob = Job.getInstance(conf);mtlinkJob.setJarByClass(mtlink.class);mtlinkJob.setJobName("multiple tables link");mtlinkJob.setMapperClass(mtlinkMapper.class);mtlinkJob.setReducerClass(mtlinkReducer.class);mtlinkJob.setOutputKeyClass(Text.class);mtlinkJob.setOutputValueClass(Text.class);Path input = new Path("/home/jinzhao/dataset/input");Path output = new Path("/home/jinzhao/dataset/output");FileInputFormat.setInputPaths(mtlinkJob, input);FileSystem fs = FileSystem.get(conf);if (fs.exists(output))fs.delete(output, true);FileOutputFormat.setOutputPath(mtlinkJob, output);mtlinkJob.waitForCompletion(true);}
}