uk.org.ogsadai.activity.transform
Class GZIPCompressionActivity

java.lang.Object
  |
  +--uk.org.ogsadai.activity.Activity
        |
        +--uk.org.ogsadai.activity.transform.GZIPCompressionActivity

public class GZIPCompressionActivity

extends Activity

An Activity to perform GZIP compression. The activity has one input and two outputs. The input is the data to be compressed, the first output is the compressed data, and the second is the compression meta-data. For information on this activity see the OGSA-DAI user doc: OGSA-DAI/doc/interaction/activities/transform/gzipCompression.html

Author:

The OGSA-DAI Project Team

Field Summary

private static java.lang.String	COPYRIGHT_NOTICE Copyright statement
private byte[]	mBuffer A buffer for temporary storage of blocks.
private java.util.zip.Checksum	mChecksum The checksum type used for the compression.
private IncrementalProcessorInputStream	mCompressedInput Used to perform the compression.
private BlockWriter	mCompressedOutput Activity output - compressed data
private BlockReader	mInput Activity input - data to be compressed
private BlockWriter	mMetadataOutput Activity output - compression meta data

Fields inherited from class uk.org.ogsadai.activity.Activity

mContext, mExternalInputs, mExternalOutputs, mInternalInputs, mInternalOutputs

Constructor Summary

GZIPCompressionActivity(org.w3c.dom.Element element)

Method Summary

private java.lang.String	getMetadata() Constructs the activity meta-data XML string.
void	initialise() This method should be overridden by subclasses to perform any initialisation they require before the process method invocations begin.
void	processBlock() Performs an iteration of the processing of an activity.
void	processFirst() This method is called during the first iteration of processing an activity.

Methods inherited from class uk.org.ogsadai.activity.Activity

cleanUp, connectsTo, createOutputPipe, getActivityConfiguration, getActivityName, getCause, getName, getObservableStatus, getProperties, getSession, getStatus, hasActivityConfiguration, hasProperties, process, setActivityName, setCompleted, setError

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

COPYRIGHT_NOTICE

private static final java.lang.String COPYRIGHT_NOTICE

Copyright statement

See Also:

Constant Field Values

mInput

private BlockReader mInput

Activity input - data to be compressed

mCompressedOutput

private BlockWriter mCompressedOutput

Activity output - compressed data

mMetadataOutput

private BlockWriter mMetadataOutput

Activity output - compression meta data

mChecksum

private java.util.zip.Checksum mChecksum

The checksum type used for the compression.

mCompressedInput

private IncrementalProcessorInputStream mCompressedInput

Used to perform the compression.

mBuffer

private byte[] mBuffer

A buffer for temporary storage of blocks.

Constructor Detail

GZIPCompressionActivity

public GZIPCompressionActivity(org.w3c.dom.Element element)
                        throws ActivitySpecificationException,
                               ActivityCreationException

Method Detail

initialise

public void initialise()
                throws ActivitySpecificationException,
                       ActivityExecutionException

Description copied from class: Activity

This method should be overridden by subclasses to perform any initialisation they require before the process method invocations begin. This might be used for setting up convenient fields to reference objects contained in the context. It shouldn't be used for opening resources. That should be done in processFirst.

Overrides:

initialise in class Activity

Throws:

ActivityExecutionException - If some system problem prevents the activity from initialising.

ActivitySpecificationException - If a problem with settings provided by a client prevents the activity from initialising.

processFirst

public void processFirst()

Description copied from class: Activity

This method is called during the first iteration of processing an activity. It can be overridden by subclasses to define some processing that should be done only once during the first iteration of the activity processing, for example evaluating a database query.

Overrides:

processFirst in class Activity

processBlock

public void processBlock()

Description copied from class: Activity

Performs an iteration of the processing of an activity. This may involve reading a block of input data and writing a block of output data, or may involve some other kind of processing. When an activity is processed by the OGSA-DAI engine, this method will be invoked repeatedly until the activity either completes or stops due to an error or termination call. An implementation of this method should invoke the setCompleted method to indicate that processing is complete, or the setError method if an error occurs that will prevent the processing from completing.

Specified by:

processBlock in class Activity

getMetadata

private final java.lang.String getMetadata()

Constructs the activity meta-data XML string.

Returns:

meta data string.