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<K, V> extends RecordWriter<K, V>{
- 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 <K extends WritableComparable<?>, V extends Writable>
- extends FileOutputFormat<K, V> {
- //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<K, V> 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<K, V> {
- /**RecordWriter的缓存*/
- private HashMap<String, RecordWriter<K, V>> 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<String, RecordWriter<K, V>>();
- }
- //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<RecordWriter<K, V>> 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<K, V> 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<K, V> 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<K, V> recordWriter = null;
- if (isCompressed) {
- Class<? extends CompressionCodec> 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<K, V>(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<K, V>(fileOut, keyValueSeparator);
- //这里我使用的我自己的OutputFormat
- recordWriter = new My_LineRead<K, V>(fileOut);
- }
- return recordWriter;
- }
- }
- }
最后就是测试类，WordCount_MulFileOut.java
- public class WordCount_MulFileOut {
- public static class wordcountMapper extends
- Mapper<LongWritable, Text, Text, IntWritable>{
- 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<Text, IntWritable, Text, IntWritable>{
- public void reduce(Text key, Iterable<IntWritable>values, 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);
- }
- }