com.onewebsql.util.io.output
Class ThresholdingOutputStream

java.lang.Object
  extended by java.io.OutputStream
      extended by com.onewebsql.util.io.output.ThresholdingOutputStream
All Implemented Interfaces:
Closeable, Flushable
Direct Known Subclasses:
DeferredFileOutputStream

public abstract class ThresholdingOutputStream
extends OutputStream

An output stream which triggers an event when a specified number of bytes of data have been written to it. The event can be used, for example, to throw an exception if a maximum has been reached, or to switch the underlying stream type when the threshold is exceeded.

This class overrides all OutputStream methods. However, these overrides ultimately call the corresponding methods in the underlying output stream implementation.

NOTE: This implementation may trigger the event before the threshold is actually reached, since it triggers when a pending write operation would cause the threshold to be exceeded.


Constructor Summary
ThresholdingOutputStream(int threshold)
          Constructs an instance of this class which will trigger an event at the specified threshold.
 
Method Summary
protected  void checkThreshold(int count)
          Checks to see if writing the specified number of bytes would cause the configured threshold to be exceeded.
 void close()
          Closes this output stream and releases any system resources associated with this stream.
 void flush()
          Flushes this output stream and forces any buffered output bytes to be written out.
 long getByteCount()
          Returns the number of bytes that have been written to this output stream.
protected abstract  OutputStream getStream()
          Returns the underlying output stream, to which the corresponding OutputStream methods in this class will ultimately delegate.
 int getThreshold()
          Returns the threshold, in bytes, at which an event will be triggered.
 boolean isThresholdExceeded()
          Determines whether or not the configured threshold has been exceeded for this output stream.
protected  void resetByteCount()
          Resets the byteCount to zero.
protected abstract  void thresholdReached()
          Indicates that the configured threshold has been reached, and that a subclass should take whatever action necessary on this event.
 void write(byte[] b)
          Writes b.length bytes from the specified byte array to this output stream.
 void write(byte[] b, int off, int len)
          Writes len bytes from the specified byte array starting at offset off to this output stream.
 void write(int b)
          Writes the specified byte to this output stream.
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

ThresholdingOutputStream

public ThresholdingOutputStream(int threshold)
Constructs an instance of this class which will trigger an event at the specified threshold.

Parameters:
threshold - The number of bytes at which to trigger an event.
Method Detail

write

public void write(int b)
           throws IOException
Writes the specified byte to this output stream.

Specified by:
write in class OutputStream
Parameters:
b - The byte to be written.
Throws:
IOException - if an error occurs.

write

public void write(byte[] b)
           throws IOException
Writes b.length bytes from the specified byte array to this output stream.

Overrides:
write in class OutputStream
Parameters:
b - The array of bytes to be written.
Throws:
IOException - if an error occurs.

write

public void write(byte[] b,
                  int off,
                  int len)
           throws IOException
Writes len bytes from the specified byte array starting at offset off to this output stream.

Overrides:
write in class OutputStream
Parameters:
b - The byte array from which the data will be written.
off - The start offset in the byte array.
len - The number of bytes to write.
Throws:
IOException - if an error occurs.

flush

public void flush()
           throws IOException
Flushes this output stream and forces any buffered output bytes to be written out.

Specified by:
flush in interface Flushable
Overrides:
flush in class OutputStream
Throws:
IOException - if an error occurs.

close

public void close()
           throws IOException
Closes this output stream and releases any system resources associated with this stream.

Specified by:
close in interface Closeable
Overrides:
close in class OutputStream
Throws:
IOException - if an error occurs.

getThreshold

public int getThreshold()
Returns the threshold, in bytes, at which an event will be triggered.

Returns:
The threshold point, in bytes.

getByteCount

public long getByteCount()
Returns the number of bytes that have been written to this output stream.

Returns:
The number of bytes written.

isThresholdExceeded

public boolean isThresholdExceeded()
Determines whether or not the configured threshold has been exceeded for this output stream.

Returns:
true if the threshold has been reached; false otherwise.

checkThreshold

protected void checkThreshold(int count)
                       throws IOException
Checks to see if writing the specified number of bytes would cause the configured threshold to be exceeded. If so, triggers an event to allow a concrete implementation to take action on this.

Parameters:
count - The number of bytes about to be written to the underlying output stream.
Throws:
IOException - if an error occurs.

resetByteCount

protected void resetByteCount()
Resets the byteCount to zero. You can call this from thresholdReached() if you want the event to be triggered again.


getStream

protected abstract OutputStream getStream()
                                   throws IOException
Returns the underlying output stream, to which the corresponding OutputStream methods in this class will ultimately delegate.

Returns:
The underlying output stream.
Throws:
IOException - if an error occurs.

thresholdReached

protected abstract void thresholdReached()
                                  throws IOException
Indicates that the configured threshold has been reached, and that a subclass should take whatever action necessary on this event. This may include changing the underlying output stream.

Throws:
IOException - if an error occurs.


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