Hadoop-Mapreduce实战（倒排索引案例（多job串联））

倒排索引案例（多job串联）

• 需求：有大量的文本（文档、网页），需要建立搜索索引
  • 第一次预期输出结果

it--a.txt	3
it--b.txt	2
it--c.txt	2
pingping--a.txt	 1
pingping--b.txt	3
pingping--c.txt	 1
ss--a.txt	2
ss--b.txt	1
ss--c.txt	1

第二次预期输出结果

it	c.txt-->2	b.txt-->2	a.txt-->3	
pingping	c.txt-->1	b.txt-->3	a.txt-->1	
ss	c.txt-->1	b.txt-->1	a.txt-->2	

第一次处理

• 第一次处理，编写OneIndexMapper

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.lib.input.FileSplit;

public class OneIndexMapper extends Mapper<LongWritable, Text, Text , IntWritable>{
   
	
	String name;
	Text k = new Text();
	IntWritable v = new IntWritable();
	
	@Override
	protected void setup(Context context)
			throws IOException, InterruptedException {
   
		// 获取文件名称
		FileSplit split = (FileSplit) context.getInputSplit();
		
		name = split.getPath().getName();
	}
	
	@Override
	protected void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
   
		// 1 获取1行
		String line = value.toString();
		
		// 2 切割
		String[] fields = line.split(" ");
		
		for (String word : fields) {
   
			// 3 拼接
			k.set(word+"--"+name);
			v.set(1);
			
			// 4 写出
			context.write(k, v);
		}
	}
}

第一次处理，编写OneIndexReducer

import java.io.IOException;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;

public class OneIndexReducer extends Reducer<Text, IntWritable, Text, IntWritable>{
   
	
	@Override
	protected void reduce(Text key, Iterable<IntWritable> values,
			Context context) throws IOException, InterruptedException {
   
		
		int count = 0;
		// 1 累加求和
		for(IntWritable value: values){
   
			count +=value.get();
		}
		
		// 2 写出
		context.write(key, new IntWritable(count));
	}
}

第一次处理，编写OneIndexDriver

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class OneIndexDriver {
   

	public static void main(String[] args) throws Exception {
   

		args = new String[] {
    "e:/input/inputoneindex", "e:/output5" };

		Configuration conf = new Configuration();

		Job job = Job.getInstance(conf);
		job.setJarByClass(OneIndexDriver.class);

		job.setMapperClass(OneIndexMapper.class);
		job.setReducerClass(OneIndexReducer.class);

		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(IntWritable.class);
		
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(IntWritable.class);

		FileInputFormat.setInputPaths(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));

		job.waitForCompletion(true);
	}
}

查看第一次输出结果

it--a.txt	3
it--b.txt	2
it--c.txt	2
pingping--a.txt	1
pingping--b.txt	3
pingping--c.txt	1
ss--a.txt	2
ss--b.txt	1
ss--c.txt	1

第二次处理

• 第二次处理，编写TwoIndexMapper

import java.io.IOException;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class TwoIndexMapper extends Mapper<LongWritable, Text, Text, Text>{
   
	Text k = new Text();
	Text v = new Text();
	
	@Override
	protected void map(LongWritable key, Text value, Context context)
			throws IOException, InterruptedException {
   
		
		// 1 获取1行数据
		String line = value.toString();
		
		// 2用“--”切割
		String[] fields = line.split("--");
		
		k.set(fields[0]);
		v.set(fields[1]);
		
		// 3 输出数据
		context.write(k, v);
	}
}

第二次处理，编写TwoIndexReducer

import java.io.IOException;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Reducer;
public class TwoIndexReducer extends Reducer<Text, Text, Text, Text> {
   

	@Override
	protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
   
		// itstar a.txt 3
		// itstar b.txt 2
		// itstar c.txt 2

		// itstar c.txt-->2 b.txt-->2 a.txt-->3

		StringBuilder sb = new StringBuilder();
        // 1 拼接
		for (Text value : values) {
   
			sb.append(value.toString().replace("\t", "-->") + "\t");
		}
		// 2 写出
		context.write(key, new Text(sb.toString()));
	}
}

第二次处理，编写TwoIndexDriver

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class TwoIndexDriver {
   

	public static void main(String[] args) throws Exception {
   

args = new String[] {
    "e:/input/inputtwoindex", "e:/output6" };

		Configuration config = new Configuration();
		Job job = Job.getInstance(config);

job.setJarByClass(TwoIndexDriver.class);
		job.setMapperClass(TwoIndexMapper.class);
		job.setReducerClass(TwoIndexReducer.class);

		job.setMapOutputKeyClass(Text.class);
		job.setMapOutputValueClass(Text.class);
		
		job.setOutputKeyClass(Text.class);
		job.setOutputValueClass(Text.class);

		FileInputFormat.setInputPaths(job, new Path(args[0]));
		FileOutputFormat.setOutputPath(job, new Path(args[1]));

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

第二次查看最终结果

it  c.txt-->2	b.txt-->2	a.txt-->3	
pingping	c.txt-->1	b.txt-->3	a.txt-->1	
ss	c.txt-->1	b.txt-->1	a.txt-->2