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courses:mapreduce-tutorial:step-29 [2012/01/29 17:26] straka |
courses:mapreduce-tutorial:step-29 [2012/01/30 00:52] straka |
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Every custom format reading keys of type '' | Every custom format reading keys of type '' | ||
- | ===== WholeFileInputFormat | + | ===== FileAsPathInputFormat |
- | We start by creating '' | + | We start by creating '' |
+ | |||
+ | When implementing new input format, we must | ||
+ | * decide whether the input files are splittable. Usually uncompressed files are splittable and compressed files are not splittable, with the exception of '' | ||
+ | * implement [[http:// | ||
+ | |||
+ | Our '' | ||
+ | <code java> | ||
+ | public class FileAsPathInputFormat extends FileInputFormat< | ||
+ | // Helper class, which does the actual work -- produce the (path, offset-length) input pair. | ||
+ | public static class FileAsPathRecordReader extends RecordReader< | ||
+ | private Path file; | ||
+ | long start, length; | ||
+ | private Text key, value; | ||
+ | |||
+ | public void initialize(InputSplit genericSplit, | ||
+ | FileSplit split = (FileSplit) genericSplit; | ||
+ | file = split.getPath(); | ||
+ | start = split.getStart(); | ||
+ | length = split.getLength(); | ||
+ | key = null; | ||
+ | value = null; | ||
+ | } | ||
+ | public boolean nextKeyValue() throws IOException { | ||
+ | if (key != null) return false; | ||
+ | |||
+ | key = new Text(file.toString()); | ||
+ | value = new Text(String.format(" | ||
+ | |||
+ | return true; | ||
+ | } | ||
+ | |||
+ | public Text getCurrentKey() { return key; } | ||
+ | public Text getCurrentValue() { return value; } | ||
+ | public float getProgress() { return (key == null) ? 0 : 1; } | ||
+ | public synchronized void close() throws IOException {} | ||
+ | } | ||
+ | |||
+ | // Use the helper class as a RecordReader in out file format. | ||
+ | public RecordReader< | ||
+ | return new FileAsPathRecordReader(); | ||
+ | } | ||
+ | |||
+ | // Allow splitting uncompressed files. | ||
+ | protected boolean isSplittable(JobContext context, Path filename) { | ||
+ | CompressionCodec codec = new CompressionCodecFactory(context.getConfiguration()).getCodec(filename); | ||
+ | return codec == null; | ||
+ | } | ||
+ | } | ||
+ | </ | ||
+ | |||
+ | ===== WholeFileInputFormat ===== | ||
- | The main functionality lays in '' | + | Next we create |
<code java> | <code java> | ||
Line 15: | Line 66: | ||
private Path file; | private Path file; | ||
int length; | int length; | ||
- | private boolean value_read; | ||
private Text key; | private Text key; | ||
private BytesWritable value; | private BytesWritable value; | ||
Line 26: | Line 76: | ||
key = null; | key = null; | ||
value = null; | value = null; | ||
- | value_read = false; | ||
FileSystem fs = file.getFileSystem(context.getConfiguration()); | FileSystem fs = file.getFileSystem(context.getConfiguration()); | ||
Line 38: | Line 87: | ||
public boolean nextKeyValue() throws IOException { | public boolean nextKeyValue() throws IOException { | ||
- | if (value_read) return false; | + | if (key != null) return false; |
byte[] data = new byte[length]; | byte[] data = new byte[length]; | ||
Line 45: | Line 94: | ||
key = new Text(file.toString()); | key = new Text(file.toString()); | ||
value = new BytesWritable(data); | value = new BytesWritable(data); | ||
- | value_read = true; | ||
return true; | return true; | ||
Line 52: | Line 100: | ||
public Text getCurrentKey() { return key; } | public Text getCurrentKey() { return key; } | ||
public BytesWritable getCurrentValue() { return value; } | public BytesWritable getCurrentValue() { return value; } | ||
- | public float getProgress() { return | + | public float getProgress() { return |
public synchronized void close() throws IOException { if (in != null) { in.close(); in = null; } } | public synchronized void close() throws IOException { if (in != null) { in.close(); in = null; } } | ||
} | } | ||
Line 66: | Line 114: | ||
} | } | ||
} | } | ||
- | |||
</ | </ | ||
+ | ===== Exercise: ParagraphTextInputFormat ===== | ||
+ | |||
+ | Implement '' | ||
+ | |||
+ | The '' | ||
+ | * if the offset of the split is 0, start reading at the beginning of the split. If the offset of the split is larger than 0, start reading at the offset and ignore first paragraph found. | ||
+ | * read all paragraphs that start before the end of the split boundary, even if they end after the split boundary. //If a paragraph starts just after the current split (i.e., on the split boundary), read it too.// |