hadoop文本转换为序列文件

在以前使用hadoop的时候因为mahout里面很多都要求输入文件时序列文件，所以涉及到把文本文件转换为序列文件或者序列文件转为文本文件（因为当时要分析mahout的源码，所以就要看到它的输入文件是什么，文本比较好看其内容）。一般这个有两种做法，其一：按照《hadoop权威指南》上面的方面直接读出序列文件然后写入一个文本；其二，编写一个job任务，直接设置输出文件的格式，这样也可以把序列文件读成文本（个人一般采用这样方法）。时隔好久，今天又重新试了下，居然不行了？，比如，我要编写一个把文本转为序列文件的java程序如下：

package mahout.fansy.canopy.transformdata;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.Text;import org.apache.hadoop.io.Writable;import org.apache.hadoop.mapreduce.Job;import org.apache.hadoop.mapreduce.Mapper;import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;import org.apache.hadoop.mapreduce.lib.output.SequenceFileOutputFormat;import org.apache.mahout.common.AbstractJob;import org.apache.mahout.math.RandomAccessSparseVector;import org.apache.mahout.math.Vector;import org.apache.mahout.math.VectorWritable;public class Text2VectorWritable extends AbstractJob{ @Overridepublic int run(String[] arg0) throws Exception {addInputOption();    addOutputOption();    if (parseArguments(arg0) == null) {      return -1;}    Path input=getInputPath();    Path output=getOutputPath();    Configuration conf=getConf();    Job job=new Job(conf,"text2vectorWritable with input:"+input.getName()); //   job.setInputFormatClass(SequenceFileInputFormat.class);    job.setOutputFormatClass(SequenceFileOutputFormat.class);    job.setMapperClass(Text2VectorWritableMapper.class);    job.setMapOutputKeyClass(Writable.class);    job.setMapOutputValueClass(VectorWritable.class);    job.setNumReduceTasks(0);    job.setJarByClass(Text2VectorWritable.class);         FileInputFormat.addInputPath(job, input);    SequenceFileOutputFormat.setOutputPath(job, output);    if (!job.waitForCompletion(true)) {        throw new InterruptedException("Canopy Job failed processing " + input);      }return 0;}public static class Text2VectorWritableMapper extends Mapper<Writable,Text,Writable,VectorWritable>{public void map(Writable key,Text value,Context context)throws IOException,InterruptedException{String[] str=value.toString().split(",");Vector vector=new RandomAccessSparseVector(str.length);for(int i=0;i<str.length;i++){vector.set(i, Double.parseDouble(str[i]));}VectorWritable va=new VectorWritable(vector);context.write(key, va);}}}

这样在运行的时候老是提示说 我的Map的value的类型不是Text，不管我设置为什么类型都会是这样的情况。后来我就想会不会是map的输出时Text的格式？，然后我就把上面的程序加入了Reducer，如下：

package mahout.fansy.canopy.transformdata;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.Path;import org.apache.hadoop.io.LongWritable;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.SequenceFileOutputFormat;import org.apache.mahout.common.AbstractJob;import org.apache.mahout.math.RandomAccessSparseVector;import org.apache.mahout.math.Vector;import org.apache.mahout.math.VectorWritable;public class Text2VectorWritableCopy extends AbstractJob{ @Overridepublic int run(String[] arg0) throws Exception {addInputOption();    addOutputOption();    if (parseArguments(arg0) == null) {      return -1;}    Path input=getInputPath();    Path output=getOutputPath();    Configuration conf=getConf();    Job job=new Job(conf,"text2vectorWritableCopy with input:"+input.getName()); //   job.setInputFormatClass(SequenceFileInputFormat.class);    job.setOutputFormatClass(SequenceFileOutputFormat.class);    job.setMapperClass(Text2VectorWritableMapper.class);    job.setMapOutputKeyClass(LongWritable.class);    job.setMapOutputValueClass(VectorWritable.class);    job.setReducerClass(Text2VectorWritableReducer.class);    job.setOutputKeyClass(LongWritable.class);    job.setOutputValueClass(VectorWritable.class);    job.setJarByClass(Text2VectorWritableCopy.class);         FileInputFormat.addInputPath(job, input);    SequenceFileOutputFormat.setOutputPath(job, output);    if (!job.waitForCompletion(true)) {        throw new InterruptedException("Canopy Job failed processing " + input);      }return 0;}public static class Text2VectorWritableMapper extends Mapper<LongWritable,Text,LongWritable,VectorWritable>{public void map(LongWritable key,Text value,Context context)throws IOException,InterruptedException{String[] str=value.toString().split(",");Vector vector=new RandomAccessSparseVector(str.length);for(int i=0;i<str.length;i++){vector.set(i, Double.parseDouble(str[i]));}VectorWritable va=new VectorWritable(vector);context.write(key, va);}}public static class Text2VectorWritableReducer extends Reducer<LongWritable,VectorWritable,LongWritable,VectorWritable>{public void reduce(LongWritable key,Iterable<VectorWritable> values,Context context)throws IOException,InterruptedException{for(VectorWritable v:values){context.write(key, v);}}}}

然后在运行，就可以了。

不过关于map的输出是否一定是text格式的，还有待论证。