大数据技术之倒排索引（多job串联)

7.8 倒排索引（多job串联）

0）需求：有大量的文本（文档、网页），需要建立搜索索引

xyg pingping
xyg ss
xyg ss

a.txt

xyg pingping
xyg pingping
pingping ss

b.txt

xyg ss
xyg pingping

c.txt

（1）第一次预期输出结果

xyg--a.txt 3
xyg--b.txt 2
xyg--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

（2）第二次预期输出结果

xyg 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

1）第一次处理

（1）第一次处理，编写OneIndexMapper

package com.xyg.mapreduce.index;
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> {

    Text k = new Text();

    @Override
    protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
        // 1 获取切片名称
        FileSplit inputSplit = (FileSplit) context.getInputSplit();
        String name = inputSplit.getPath().getName();

        // 2 获取1行
        String line = value.toString();

        // 3 截取
        String[] words = line.split(" ");

        // 4 把每个单词和切片名称关联起来
        for (String word : words) {
            k.set(word + "--" + name);
            
            context.write(k, new IntWritable(1));
        }
    }
}

（2）第一次处理，编写OneIndexReducer

package com.xyg.mapreduce.index;
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;
        // 累加和
        for(IntWritable value: values){
            count +=value.get();
        }
        
        // 写出
        context.write(key, new IntWritable(count));
    }
}

（3）第一次处理，编写OneIndexDriver

package com.xyg.mapreduce.index;
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:/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);
    }
}

（4）查看第一次输出结果

xyg--a.txt    3
xyg--b.txt    2
xyg--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

2）第二次处理

（1）第二次处理，编写TwoIndexMapper

package com.xyg.mapreduce.index;
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);
    }
}

（2）第二次处理，编写TwoIndexReducer

package com.xyg.mapreduce.index;
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 {
        // atguigu a.txt 3
        // atguigu b.txt 2
        // atguigu c.txt 2

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

        StringBuilder sb = new StringBuilder();

        for (Text value : values) {
            sb.append(value.toString().replace("\t", "-->") + "\t");
        }
        
        context.write(key, new Text(sb.toString()));
    }
}

（3）第二次处理，编写TwoIndexDriver

package com.xyg.mapreduce.index;
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:/inputtwoindex", "e:/output6" };

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

        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]));

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

（4）第二次查看最终结果

xyg     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