uk.ac.starlink.table
Class OnceRowPipe

java.lang.Object
  extended by uk.ac.starlink.table.OnceRowPipe
All Implemented Interfaces:
RowPipe, RowSequence, TableSink

public class OnceRowPipe
extends java.lang.Object
implements RowPipe, RowSequence

Streaming RowPipe implementation which provides a one-shot table. The returned table is unusual in that it can only return a RowSequence once. This violates the normal rules of the StarTable interface. Any calls beyond the first to waitForStarTable().getRowSequence() will throw a UnrepeatableSequenceException.

Since:
10 Feb 2005

Constructor Summary
OnceRowPipe()
          Constructs a new streaming row store with a default buffer size.
OnceRowPipe(int queueSize)
          Constructs a new streaming row store with a given buffer size.
 
Method Summary
 void acceptMetadata(StarTable meta)
          Takes delivery of a row-less StarTable object which defines the metadata of the table to be transmitted.
 void acceptRow(java.lang.Object[] row)
          Takes delivery of one row of data.
 void close()
          Indicates that this sequence will not be required any more.
 void endRows()
          Signals that there are no more rows to be transmitted.
 java.lang.Object getCell(int icol)
          Returns the contents of a cell in the current row.
 java.lang.Object[] getRow()
          Returns the contents of the current table row, as an array with the same number of elements as there are columns in this table.
 boolean next()
          Attempts to advances the current row to the next one.
 void setError(java.io.IOException error)
          May be called by the writing stream to set an I/O error on the pipe.
 StarTable waitForStarTable()
          Returns a non-random table whose first call to getRowSequence will return a sequence that steps through the same rows which are being written to this sink.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

OnceRowPipe

public OnceRowPipe()
Constructs a new streaming row store with a default buffer size.


OnceRowPipe

public OnceRowPipe(int queueSize)
Constructs a new streaming row store with a given buffer size.

Parameters:
queueSize - the maximum number of rows buffered between write and read before acceptRow will block
Method Detail

setError

public void setError(java.io.IOException error)
Description copied from interface: RowPipe
May be called by the writing stream to set an I/O error on the pipe. This error should be passed on to the reading end by throwing an error with e as its cause from one of the read methods. If an error has already been set by a previous call of this method, this has no effect (only the first error is set).

Specified by:
setError in interface RowPipe
Parameters:
error - exception to pass to readers

acceptMetadata

public void acceptMetadata(StarTable meta)
Description copied from interface: TableSink
Takes delivery of a row-less StarTable object which defines the metadata of the table to be transmitted. If the number of rows that will be transmitted via subsequent calls to acceptRow is known, this value should be made available as the row count of meta (StarTable.getRowCount()); if it is not known, the row count should be -1. However, this object should not attempt to read any of meta's cell data.

The data to be transmitted in subsequent calls of acceptRow must match the metadata transmitted in this call in the same way that rows of a StarTable must match its own metadata (number and content clases of columns etc). If this sink cannot dispose of a table corresponding to meta then it may throw a TableFormatException - this may be the case if for instance meta has columns with types that this sink can't deal with.

Specified by:
acceptMetadata in interface TableSink
Parameters:
meta - table metadata object

acceptRow

public void acceptRow(java.lang.Object[] row)
               throws java.io.IOException
Description copied from interface: TableSink
Takes delivery of one row of data. row is an array of objects comprising the contents of one row of the table being transmitted. The number and classes of the elements of row are described by the metadata object previously accepted.

Specified by:
acceptRow in interface TableSink
Parameters:
row - table data row
Throws:
java.io.IOException

endRows

public void endRows()
Description copied from interface: TableSink
Signals that there are no more rows to be transmitted.

Specified by:
endRows in interface TableSink

waitForStarTable

public StarTable waitForStarTable()
                           throws java.io.IOException
Returns a non-random table whose first call to getRowSequence will return a sequence that steps through the same rows which are being written to this sink. The getRowSequence method can only be called once; any subsequent attempts to call it will result in a UnrepeatableSequenceException. This method will block until acceptMetadata(uk.ac.starlink.table.StarTable) has been called.

Specified by:
waitForStarTable in interface RowPipe
Returns:
one-shot streaming sequential table
Throws:
java.io.IOException - if one has previously been set using setError(java.io.IOException)

next

public boolean next()
             throws java.io.IOException
Description copied from interface: RowSequence
Attempts to advances the current row to the next one. If true is returned the attempt has been successful, and if false is returned there are no more rows in this sequence. Since the initial position of a RowSequence is before the first row, this method must be called before current row data can be accessed using the RowSequence.getCell(int) or RowSequence.getRow() methods.

Specified by:
next in interface RowSequence
Returns:
true iff this sequence has been advanced to the next row
Throws:
java.io.IOException - if there is some error

getRow

public java.lang.Object[] getRow()
Description copied from interface: RowSequence
Returns the contents of the current table row, as an array with the same number of elements as there are columns in this table. An unchecked exception will be thrown if there is no current row (next has not yet been called).

Specified by:
getRow in interface RowSequence
Returns:
an array of the objects in each cell in row irow

getCell

public java.lang.Object getCell(int icol)
Description copied from interface: RowSequence
Returns the contents of a cell in the current row. The class of the returned object should be the same as, or a subclass of, the class returned by getColumnInfo(icol).getContentClass(). An unchecked exception will be thrown if there is no current row (next has not yet been called).

Specified by:
getCell in interface RowSequence
Returns:
the contents of cell icol in the current row

close

public void close()
Description copied from interface: RowSequence
Indicates that this sequence will not be required any more. This should release resources associated with this object. The effect of calling any of the other methods following a close is undefined.

Specified by:
close in interface RowSequence

Copyright © 2004 CLRC: Central Laboratory of the Research Councils. All rights reserved.