系統環境
Linux Ubuntu 16.04
jdk-7u75-linux-x64
hadoop-2.6.0-cdh5.4.5
hadoop-2.6.0-eclipse-cdh5.4.5.jar
eclipse-java-juno-SR2-linux-gtk-x86_64
任務內容
在電商網站中,用戶進入頁面瀏覽商品時會產生訪問日誌,記錄用戶對商品的訪問情況,現有goods_visit2表,包含(goods_id,click_num)兩個字段,數據內容如下:
goods_id click_num
1010037 100
1010102 100
1010152 97
1010178 96
1010280 104
1010320 103
1010510 104
1010603 96
1010637 97
編寫MapReduce代碼,功能爲根據商品的點擊次數(click_num)進行降序排序,再根據goods_id升序排序,並輸出所有商品。
輸出結果如下:
點擊次數 商品id
------------------------------------------------
104 1010280
104 1010510
------------------------------------------------
103 1010320
------------------------------------------------
100 1010037
100 1010102
------------------------------------------------
97 1010152
97 1010637
------------------------------------------------
96 1010178
96 1010603
任務步驟
1.切換到/apps/hadoop/sbin目錄下,開啓Hadoop。
cd /apps/hadoop/sbin
./start-all.sh
2.在Linux本地新建/data/mapreduce8目錄。
mkdir -p /data/mapreduce8
3.在Linux中切換到/data/mapreduce8目錄下,用wget命令從http://192.168.1.100:60000/allfiles/mapreduce8/goods_visit2網址上下載文本文件goods_visit2。
cd /data/mapreduce8
wget http://192.168.1.100:60000/allfiles/mapreduce8/goods_visit2
然後在當前目錄下用wget命令從http://192.168.1.100:60000/allfiles/mapreduce8/hadoop2lib.tar.gz網址上下載項目用到的依賴包。
wget http://192.168.1.100:60000/allfiles/mapreduce8/hadoop2lib.tar.gz
將hadoop2lib.tar.gz解壓到當前目錄下。
tar zxvf hadoop2lib.tar.gz
4.首先在HDFS上新建/mymapreduce8/in目錄,然後將Linux本地/data/mapreduce8目錄下的goods_visit2文件導入到HDFS的/mymapreduce8/in目錄中。
hadoop fs -mkdir -p /mymapreduce8/in
hadoop fs -put /data/mapreduce8/goods_visit2 /mymapreduce8/in
5.新建Java Project項目,項目名爲mapreduce8
在mapreduce8項目下新建一個package包,包名爲mapreduce,在mapreduce的package包下新建一個SecondarySort類
6.添加項目所需依賴的jar包,右鍵單擊mapreduce8,新建一個文件夾hadoop2lib,用於存放項目所需的jar包
將/data/mapreduce8目錄下,hadoop2lib目錄中的jar包,拷貝到eclipse中mapreduce8項目的hadopo2lib目錄下,選中hadoop2lib目錄下所有jar包,並添加到Build Path中。
7.編寫Java代碼,並描述其設計思路
二次排序:在mapreduce中,所有的key是需要被比較和排序的,並且是二次,先根據partitioner,再根據大小。而本例中也是要比較兩次。先按照第一字段排序,然後在第一字段相同時按照第二字段排序。根據這一點,我們可以構造一個複合類IntPair,他有兩個字段,先利用分區對第一字段排序,再利用分區內的比較對第二字段排序。Java代碼主要分爲四部分:自定義key,自定義分區函數類,map部分,reduce部分。
自定義key的代碼:
public static class IntPair implements WritableComparable<IntPair>
{
int first; //第一個成員變量
int second; //第二個成員變量
public void set(int left, int right)
{
first = left;
second = right;
}
public int getFirst()
{
return first;
}
public int getSecond()
{
return second;
}
@Override
//反序列化,從流中的二進制轉換成IntPair
public void readFields(DataInput in) throws IOException
{
// TODO Auto-generated method stub
first = in.readInt();
second = in.readInt();
}
@Override
//序列化,將IntPair轉化成使用流傳送的二進制
public void write(DataOutput out) throws IOException
{
// TODO Auto-generated method stub
out.writeInt(first);
out.writeInt(second);
}
@Override
//key的比較
public int compareTo(IntPair o)
{
// TODO Auto-generated method stub
if (first != o.first)
{
return first < o.first ? 1 : -1;
}
else if (second != o.second)
{
return second < o.second ? -1 : 1;
}
else
{
return 0;
}
}
@Override
public int hashCode()
{
return first * 157 + second;
}
@Override
public boolean equals(Object right)
{
if (right == null)
return false;
if (this == right)
return true;
if (right instanceof IntPair)
{
IntPair r = (IntPair) right;
return r.first == first && r.second == second;
}
else
{
return false;
}
}
}
所有自定義的key應該實現接口WritableComparable,因爲是可序列的並且可比較的,並重載方法。該類中包含以下幾種方法:1.反序列化,從流中的二進制轉換成IntPair 方法爲public void readFields(DataInput in) throws IOException 2.序列化,將IntPair轉化成使用流傳送的二進制 方法爲public void write(DataOutput out)3. key的比較 public int compareTo(IntPair o) 另外新定義的類應該重寫的兩個方法 public int hashCode() 和public boolean equals(Object right) 。
分區函數類代碼
public static class FirstPartitioner extends Partitioner<IntPair, IntWritable>
{
@Override
public int getPartition(IntPair key, IntWritable value,int numPartitions)
{
return Math.abs(key.getFirst() * 127) % numPartitions;
}
}
對key進行分區,根據自定義key中first乘以127取絕對值在對numPartions取餘來進行分區。這主要是爲實現第一次排序。
分組函數類代碼
public static class GroupingComparator extends WritableComparator
{
protected GroupingComparator()
{
super(IntPair.class, true);
}
@Override
//Compare two WritableComparables.
public int compare(WritableComparable w1, WritableComparable w2)
{
IntPair ip1 = (IntPair) w1;
IntPair ip2 = (IntPair) w2;
int l = ip1.getFirst();
int r = ip2.getFirst();
return l == r ? 0 : (l < r ? -1 : 1);
}
}
分組函數類。在reduce階段,構造一個key對應的value迭代器的時候,只要first相同就屬於同一個組,放在一個value迭代器。這是一個比較器,需要繼承WritableComparator。
map代碼:
public static class Map extends Mapper<LongWritable, Text, IntPair, IntWritable>
{
//自定義map
private final IntPair intkey = new IntPair();
private final IntWritable intvalue = new IntWritable();
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
{
String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
int left = 0;
int right = 0;
if (tokenizer.hasMoreTokens())
{
left = Integer.parseInt(tokenizer.nextToken());
if (tokenizer.hasMoreTokens())
right = Integer.parseInt(tokenizer.nextToken());
intkey.set(right, left);
intvalue.set(left);
context.write(intkey, intvalue);
}
}
}
在map階段,使用job.setInputFormatClass定義的InputFormat將輸入的數據集分割成小數據塊splites,同時InputFormat提供一個RecordReder的實現。本例子中使用的是TextInputFormat,他提供的RecordReder會將文本的一行的行號作爲key,這一行的文本作爲value。這就是自定義Map的輸入是<LongWritable, Text>的原因。然後調用自定義Map的map方法,將一個個<LongWritable, Text>鍵值對輸入給Map的map方法。注意輸出應該符合自定義Map中定義的輸出<IntPair, IntWritable>。最終是生成一個List<IntPair, IntWritable>。在map階段的最後,會先調用job.setPartitionerClass對這個List進行分區,每個分區映射到一個reducer。每個分區內又調用job.setSortComparatorClass設置的key比較函數類排序。可以看到,這本身就是一個二次排序。如果沒有通過job.setSortComparatorClass設置key比較函數類,則使用key實現compareTo方法。在本例子中,使用了IntPair實現compareTo方法。
Reduce代碼:
public static class Reduce extends Reducer<IntPair, IntWritable, Text, IntWritable>
{
private final Text left = new Text();
private static final Text SEPARATOR = new Text("------------------------------------------------");
public void reduce(IntPair key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException
{
context.write(SEPARATOR, null);
left.set(Integer.toString(key.getFirst()));
System.out.println(left);
for (IntWritable val : values)
{
context.write(left, val);
//System.out.println(val);
}
}
}
在reduce階段,reducer接收到所有映射到這個reducer的map輸出後,也是會調用job.setSortComparatorClass設置的key比較函數類對所有數據對排序。然後開始構造一個key對應的value迭代器。這時就要用到分組,使用job.setGroupingComparatorClass設置的分組函數類。只要這個比較器比較的兩個key相同,他們就屬於同一個組,它們的value放在一個value迭代器,而這個迭代器的key使用屬於同一個組的所有key的第一個key。最後就是進入Reducer的reduce方法,reduce方法的輸入是所有的key和它的value迭代器。同樣注意輸入與輸出的類型必須與自定義的Reducer中聲明的一致。
完整代碼:
package mapreduce;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.io.WritableComparable;
import org.apache.hadoop.io.WritableComparator;
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.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
public class SecondarySort
{
public static class IntPair implements WritableComparable<IntPair>
{
int first;
int second;
public void set(int left, int right)
{
first = left;
second = right;
}
public int getFirst()
{
return first;
}
public int getSecond()
{
return second;
}
@Override
public void readFields(DataInput in) throws IOException
{
// TODO Auto-generated method stub
first = in.readInt();
second = in.readInt();
}
@Override
public void write(DataOutput out) throws IOException
{
// TODO Auto-generated method stub
out.writeInt(first);
out.writeInt(second);
}
@Override
public int compareTo(IntPair o)
{
// TODO Auto-generated method stub
if (first != o.first)
{
return first < o.first ? 1 : -1;
}
else if (second != o.second)
{
return second < o.second ? -1 : 1;
}
else
{
return 0;
}
}
@Override
public int hashCode()
{
return first * 157 + second;
}
@Override
public boolean equals(Object right)
{
if (right == null)
return false;
if (this == right)
return true;
if (right instanceof IntPair)
{
IntPair r = (IntPair) right;
return r.first == first && r.second == second;
}
else
{
return false;
}
}
}
public static class FirstPartitioner extends Partitioner<IntPair, IntWritable>
{
@Override
public int getPartition(IntPair key, IntWritable value,int numPartitions)
{
return Math.abs(key.getFirst() * 127) % numPartitions;
}
}
public static class GroupingComparator extends WritableComparator
{
protected GroupingComparator()
{
super(IntPair.class, true);
}
@Override
//Compare two WritableComparables.
public int compare(WritableComparable w1, WritableComparable w2)
{
IntPair ip1 = (IntPair) w1;
IntPair ip2 = (IntPair) w2;
int l = ip1.getFirst();
int r = ip2.getFirst();
return l == r ? 0 : (l < r ? -1 : 1);
}
}
public static class Map extends Mapper<LongWritable, Text, IntPair, IntWritable>
{
private final IntPair intkey = new IntPair();
private final IntWritable intvalue = new IntWritable();
public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException
{
String line = value.toString();
StringTokenizer tokenizer = new StringTokenizer(line);
int left = 0;
int right = 0;
if (tokenizer.hasMoreTokens())
{
left = Integer.parseInt(tokenizer.nextToken());
if (tokenizer.hasMoreTokens())
right = Integer.parseInt(tokenizer.nextToken());
intkey.set(right, left);
intvalue.set(left);
context.write(intkey, intvalue);
}
}
}
public static class Reduce extends Reducer<IntPair, IntWritable, Text, IntWritable>
{
private final Text left = new Text();
private static final Text SEPARATOR = new Text("------------------------------------------------");
public void reduce(IntPair key, Iterable<IntWritable> values,Context context) throws IOException, InterruptedException
{
context.write(SEPARATOR, null);
left.set(Integer.toString(key.getFirst()));
System.out.println(left);
for (IntWritable val : values)
{
context.write(left, val);
//System.out.println(val);
}
}
}
public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException
{
Configuration conf = new Configuration();
Job job = new Job(conf, "secondarysort");
job.setJarByClass(SecondarySort.class);
job.setMapperClass(Map.class);
job.setReducerClass(Reduce.class);
job.setPartitionerClass(FirstPartitioner.class);
job.setGroupingComparatorClass(GroupingComparator.class);
job.setMapOutputKeyClass(IntPair.class);
job.setMapOutputValueClass(IntWritable.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setInputFormatClass(TextInputFormat.class);
job.setOutputFormatClass(TextOutputFormat.class);
String[] otherArgs=new String[2];
otherArgs[0]="hdfs://localhost:9000/mymapreduce8/in/goods_visit2";
otherArgs[1]="hdfs://localhost:9000/mymapreduce8/out";
FileInputFormat.setInputPaths(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
8.在SecondarySort類文件中,右鍵並點擊=>Run As=>Run on Hadoop選項。
9.待執行完畢後,進入命令模式,在hdfs上從Java代碼指定的輸出路徑中查看實驗結果。
hadoop fs -ls /mymapreduce8/out
hadoop fs -cat /mymapreduce8/out/part-r-00000