TFile.Reader (Hadoop 0.20.1+169.88 API)
Date: 2010-05-20

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## org.apache.hadoop.io.file.tfile
Class TFile.Reader

    java.lang.Object
      org.apache.hadoop.io.file.tfile.TFile.Reader

All Implemented Interfaces:
  Closeable

Enclosing class:
  TFile

    public static class TFile.Reader

extends Object
implements Closeable

TFile Reader. Users may only read TFiles by creating TFile.Reader.Scanner. objects. A scanner may scan the whole TFile (`createScanner()` ) , a portion of TFile based on byte offsets ( `createScanner(long, long)`), or a portion of TFile with keys fall in a certain key range (for sorted TFile only, `createScanner(byte[], byte[])` or `createScanner(RawComparable, RawComparable)`).

Nested Class Summary
`static class` | `TFile.Reader.Scanner` The TFile Scanner.

Constructor Summary
`TFile.Reader(FSDataInputStream fsdis, long fileLength, Configuration conf)` Constructor

Method Summary
`void` | `close()` Close the reader.
`TFile.Reader.Scanner` | `createScanner()` Get a scanner than can scan the whole TFile.
`TFile.Reader.Scanner` | `createScanner(byte[] beginKey, byte[] endKey)` Get a scanner that covers a portion of TFile based on keys.
`TFile.Reader.Scanner` | `createScanner(long offset, long length)` Get a scanner that covers a portion of TFile based on byte offsets.
`TFile.Reader.Scanner` | `createScanner(RawComparable beginKey, RawComparable endKey)` Get a scanner that covers a specific key range.
`Comparator<RawComparable>` | `getComparator()` Get an instance of the RawComparator that is constructed based on the string comparator representation.
`String` | `getComparatorName()` Get the string representation of the comparator.
`Comparator<TFile.Reader.Scanner.Entry>` | `getEntryComparator()` Get a Comparator object to compare Entries.
`long` | `getEntryCount()` Get the number of key-value pair entries in TFile.
`RawComparable` | `getFirstKey()` Get the first key in the TFile.
`RawComparable` | `getKeyNear(long offset)` Get a sample key that is within a block whose starting offset is greater than or equal to the specified offset.
`RawComparable` | `getLastKey()` Get the last key in the TFile.
`DataInputStream` | `getMetaBlock(String name)` Stream access to a meta block.``
`boolean` | `isSorted()` Is the TFile sorted?

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### TFile.Reader

    public TFile.Reader(FSDataInputStream fsdis,
                        long fileLength,
                        Configuration conf)
                 throws IOException

  Constructor

  Parameters:
    `fsdis` - FS input stream of the TFile.
    `fileLength` - The length of TFile. This is required because we have no easy way of knowing the actual size of the input file through the File input stream.
    `conf` -
  Throws:
    `IOException`

Method Detail

### close

    public void close()
               throws IOException

  Close the reader. The state of the Reader object is undefined after close. Calling close() for multiple times has no effect.

  Specified by:
    `close` in interface `Closeable`
  Throws:
    `IOException`

### getComparatorName

    public String getComparatorName()

  Get the string representation of the comparator.

  Returns:
    If the TFile is not sorted by keys, an empty string will be returned. Otherwise, the actual comparator string that is provided during the TFile creation time will be returned.

### isSorted

    public boolean isSorted()

  Is the TFile sorted?

  Returns:
    true if TFile is sorted.

### getEntryCount

    public long getEntryCount()

  Get the number of key-value pair entries in TFile.

  Returns:
    the number of key-value pairs in TFile

### getFirstKey

    public RawComparable getFirstKey()
                              throws IOException

  Get the first key in the TFile.

  Returns:
    The first key in the TFile.
  Throws:
    `IOException`

### getLastKey

    public RawComparable getLastKey()
                             throws IOException

  Get the last key in the TFile.

  Returns:
    The last key in the TFile.
  Throws:
    `IOException`

### getEntryComparator

    public Comparator<TFile.Reader.Scanner.Entry> getEntryComparator()

  Get a Comparator object to compare Entries. It is useful when you want stores the entries in a collection (such as PriorityQueue) and perform sorting or comparison among entries based on the keys without copying out the key.

  Returns:
    An Entry Comparator..

### getComparator

    public Comparator<RawComparable> getComparator()

  Get an instance of the RawComparator that is constructed based on the string comparator representation.

  Returns:
    a Comparator that can compare RawComparable's.

### getMetaBlock

    public DataInputStream getMetaBlock(String name)
                                 throws IOException,
                                        MetaBlockDoesNotExist

  Stream access to a meta block.``

  Parameters:
    `name` - The name of the meta block.
  Returns:
    The input stream.
  Throws:
    `IOException` - on I/O error.
    `MetaBlockDoesNotExist` - If the meta block with the name does not exist.

### getKeyNear

    public RawComparable getKeyNear(long offset)
                             throws IOException

  Get a sample key that is within a block whose starting offset is greater than or equal to the specified offset.

  Parameters:
    `offset` - The file offset.
  Returns:
    the key that fits the requirement; or null if no such key exists (which could happen if the offset is close to the end of the TFile).
  Throws:
    `IOException`

### createScanner

    public TFile.Reader.Scanner createScanner()
                                       throws IOException

  Get a scanner than can scan the whole TFile.

  Returns:
    The scanner object. A valid Scanner is always returned even if the TFile is empty.
  Throws:
    `IOException`

### createScanner

    public TFile.Reader.Scanner createScanner(long offset,
                                              long length)
                                       throws IOException

  Get a scanner that covers a portion of TFile based on byte offsets.

  Parameters:
    `offset` - The beginning byte offset in the TFile.
    `length` - The length of the region.
  Returns:
    The actual coverage of the returned scanner tries to match the specified byte-region but always round up to the compression block boundaries. It is possible that the returned scanner contains zero key-value pairs even if length is positive.
  Throws:
    `IOException`

### createScanner

    public TFile.Reader.Scanner createScanner(byte[] beginKey,
                                              byte[] endKey)
                                       throws IOException

  Get a scanner that covers a portion of TFile based on keys.

  Parameters:
    `beginKey` - Begin key of the scan (inclusive). If null, scan from the first key-value entry of the TFile.
    `endKey` - End key of the scan (exclusive). If null, scan up to the last key-value entry of the TFile.
  Returns:
    The actual coverage of the returned scanner will cover all keys greater than or equal to the beginKey and less than the endKey.
  Throws:
    `IOException`

### createScanner

    public TFile.Reader.Scanner createScanner(RawComparable beginKey,
                                              RawComparable endKey)
                                       throws IOException

  Get a scanner that covers a specific key range.

  Parameters:
    `beginKey` - Begin key of the scan (inclusive). If null, scan from the first key-value entry of the TFile.
    `endKey` - End key of the scan (exclusive). If null, scan up to the last key-value entry of the TFile.
  Returns:
    The actual coverage of the returned scanner will cover all keys greater than or equal to the beginKey and less than the endKey.
  Throws:
    `IOException`

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