A simple grep program made by hadoop, which can extract lines containing certain strings from documents
Copy the code code as follows:
/*
* A simple grep program that can extract lines containing certain strings from documents
*/
public class grep extends Configured implements Tool{
public static class grepMap extends Mapper<LongWritable, Text, Text,NullWritable>{
public void map(LongWritable line,Text value,Context context) throws IOException, InterruptedException{
//Get parameters through Configuration
String str = context.getConfiguration().get("grep");
if(value.toString().contains(str)){
context.write(value, NullWritable.get());
}
}
}
@Override
public int run(String[] args) throws Exception {
if(args.length!=3){
System.out.println("ERROR");
System.exit(1);
}
Configuration configuration = getConf();
//pass parameters
configuration.set("grep", args[2]);
Job job = new Job(configuration,"grep");
job.setJarByClass(grep.class);
job.setMapperClass(grepMap.class);
job.setNumReduceTasks(0);
job.setMapOutputKeyClass(Text.class);
job.setOutputValueClass(NullWritable.class);
Path in = new Path(args[0]);
Path out = new Path(args[1]);
FileSystem fileSystem = out.getFileSystem(configuration);
if(fileSystem.exists(out))
fileSystem.delete(out, true);
FileInputFormat.addInputPath(job, in);
FileOutputFormat.setOutputPath(job, out);
System.exit(job.waitForCompletion(true)?0:1);
return 0;
}