这两天在网上看了个MapReduce的多文件输出的帖子： http://blog.csdn.net/inkfish。写的不错。
我试着完成了一下。也是分为三个文件：我这三个文件，跟原作者的稍有不同。其中有些类是我原来写的，我直接拷贝过来的，所以有点不同。
My_LineRead.java
public class My_LineRead extends RecordWriter{ private static final String utf8 = "UTF-8"; private static final String colon = "----"; //划分符号 private static final byte[] newline; static { try { newline = "/n".getBytes(utf8); } catch (UnsupportedEncodingException uee) { throw new IllegalArgumentException("can't find " + utf8 + " encoding"); } } protected DataOutputStream out; private final byte[] keyValueSeparator; public My_LineRead(DataOutputStream out) { this(out, colon); //调用下面的构造函数 } public My_LineRead(DataOutputStream out, String keyValueSeparator) { // TODO Auto-generated constructor stub this.out = out; try { this.keyValueSeparator = keyValueSeparator.getBytes(utf8); } catch (UnsupportedEncodingException e) { // TODO Auto-generated catch block throw new IllegalArgumentException("can't find " + utf8 + " encoding"); } } @Override public void close(TaskAttemptContext arg0) throws IOException, InterruptedException { // TODO Auto-generated method stub out.close(); } @Override public void write(K key, V value) throws IOException, InterruptedException { if (!(key == null && key instanceof NullWritable)){ //如果key不为空者输出key if ((Object)key instanceof Text){ Text to = (Text) key; out.write(to.getBytes(), 0, to.getLength()); } else { out.write(key.toString().getBytes(utf8)); } out.write(keyValueSeparator); } if (!(value == null && value instanceof NullWritable)){ //如果value不为空则输出value if ((Object)value instanceof Text){ Text to = (Text) value; out.write(to.getBytes(), 0, to.getLength()); } else { out.write(value.toString().getBytes(utf8)); } out.write(newline); } } }
MyMultipleOutputFormat.java //这个类，我添加了些注释便于理解
public abstract class MyMultipleOutputFormat , V extends Writable> extends FileOutputFormat { //接口类，需要在主程序中实现generateFileNameForKeyValue来获取文件名 private MultiRecordWriter writer = null; @Override public RecordWriter getRecordWriter(TaskAttemptContext job) throws IOException, InterruptedException { // TODO Auto-generated method stub //如果第一次调用那么writer=null if (writer == null) { //getTaskOutputPath获取output路径 writer = new MultiRecordWriter(job, getTaskOutputPath(job)); } return writer; } private Path getTaskOutputPath(TaskAttemptContext conf) throws IOException { Path workPath = null; OutputCommitter committer = super.getOutputCommitter(conf); if (committer instanceof FileOutputCommitter) { workPath = ((FileOutputCommitter) committer).getWorkPath(); } else { Path outputPath = super.getOutputPath(conf); if (outputPath == null) { throw new IOException("Undefined job output-path"); } workPath = outputPath; } return workPath; } /**通过key, value, conf来确定输出文件名（含扩展名）*/ //返回值就是文件名。可以根据key,value来判断 protected abstract String generateFileNameForKeyValue(K key, V value, Configuration conf); //MultiRecordWriter类 public class MultiRecordWriter extends RecordWriter { /**RecordWriter的缓存*/ private HashMap> recordWriters = null; private TaskAttemptContext job = null; /**输出目录*/ private Path workPath = null; //构造函数 public MultiRecordWriter(TaskAttemptContext job, Path workPath) { super(); this.job = job; this.workPath = workPath; recordWriters = new HashMap>(); } //关闭，应该可能是多个文件进行关闭，所有采用循环 //recordWriters.values() 就是指的getBaseRecordWriter返回的值。 @Override public void close(TaskAttemptContext context) throws IOException, InterruptedException { Iterator> values = this.recordWriters.values().iterator(); while (values.hasNext()) { values.next().close(context); } this.recordWriters.clear(); } @Override public void write(K key, V value) throws IOException, InterruptedException { //得到输出文件名 String baseName = generateFileNameForKeyValue(key, value, job.getConfiguration()); //如果recordWriters里没有文件名，那么就建立。否则就直接写值。 RecordWriter rw = this.recordWriters.get(baseName); if (rw == null) { rw = getBaseRecordWriter(job, baseName); //放入HashMap this.recordWriters.put(baseName, rw); } rw.write(key, value); } // ${mapred.out.dir}/_temporary/_${taskid}/${nameWithExtension} private RecordWriter getBaseRecordWriter(TaskAttemptContext job, String baseName) throws IOException, InterruptedException { //获取配置文件 Configuration conf = job.getConfiguration(); //查看是否使用解码器 boolean isCompressed = getCompressOutput(job); String keyValueSeparator = ","; RecordWriter recordWriter = null; if (isCompressed) { Class codecClass = getOutputCompressorClass(job, GzipCodec.class); CompressionCodec codec = ReflectionUtils.newInstance(codecClass, conf); Path file = new Path(workPath, baseName + codec.getDefaultExtension()); FSDataOutputStream fileOut = file.getFileSystem(conf).create(file, false); recordWriter = new My_LineRead(new DataOutputStream(codec .createOutputStream(fileOut)), keyValueSeparator); } //如果不使用解码器 else { Path file = new Path(workPath, baseName); FSDataOutputStream fileOut = file.getFileSystem(conf).create(file, false); //recordWriter = new My_LineRead(fileOut, keyValueSeparator); //这里我使用的我自己的OutputFormat recordWriter = new My_LineRead(fileOut); } return recordWriter; } } }
最后就是测试类，WordCount_MulFileOut.java
public class WordCount_MulFileOut { public static class wordcountMapper extends Mapper{ private final static IntWritable one = new IntWritable(1); private Text word = new Text(); public void map(LongWritable key, Text value, Context context)throws IOException, InterruptedException{ String line = value.toString(); StringTokenizer itr = new StringTokenizer(line); while(itr.hasMoreElements()){ word.set(itr.nextToken()); context.write(word, one); } } } public static class wordcountReduce extends Reducer{ public void reduce(Text key, Iterablevalues, Context context)throws IOException, InterruptedException{ int sum = 0; for (IntWritable str : values){ sum += str.get(); } context.write(key, new IntWritable(sum)); } } public static class MyMultiple extends MyMultipleOutputFormat{ @Override protected String generateFileNameForKeyValue(WritableComparable key, Writable value, Configuration conf) { // TODO Auto-generated method stub return "other.txt"; } } public static void main(String args[])throws Exception{ Configuration conf = new Configuration(); Job job = new Job(conf, "wordcount"); job.setJarByClass(WordCount_MulFileOut.class); job.setInputFormatClass(TextInputFormat.class); job.setOutputFormatClass(MyMultiple.class); job.setOutputKeyClass(Text.class); job.setOutputValueClass(IntWritable.class); job.setMapperClass(wordcountMapper.class); job.setReducerClass(wordcountReduce.class); job.setCombinerClass(wordcountReduce.class); FileInputFormat.setInputPaths(job, new Path(args[1])); FileOutputFormat.setOutputPath(job, new Path(args[2])); job.waitForCompletion(true); } }
