uk.ac.starlink.util.gui

Class Downloader<T>

java.lang.Object

uk.ac.starlink.util.gui.Downloader<T>

public abstract class Downloader<T>
extends Object

Manages downloading of data that only needs to be got once.

Since:

13 Jun 2014

Author:

Mark Taylor

Constructor Summary

Constructors

Constructor and Description
Downloader(Class<T> clazz, String dataDescription) Constructor.

Method Summary

Modifier and Type	Method and Description
void	addActionListener(ActionListener listener) Adds a listener that will be notified if the data acquisition status changes.
abstract T	attemptReadData() Performs the actual download.
void	clearData() Resets the state of this downloader, as if no download attempt had been made.
JComponent	createMonitorComponent() Returns a little component that monitors status of this downloader.
T	getData() Immediately returns the downloaded data, or null if it has not been downloaded, or if a download has failed.
boolean	isComplete() Indicates whether the data has been downloaded.
void	removeActionListener(ActionListener listener) Removes a previously added listener.
void	setData(T value) Sets the state of this downloader as if it had just downloaded the given data item.
T	waitForData() Downloads the data if necessary, and returns its content.

Methods inherited from class java.lang.Object

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

Constructor Detail

Downloader

public Downloader(Class<T> clazz,
                  String dataDescription)

Constructor.

Parameters:

clazz - type of data downloaded

dataDescription - short description of downloaded data, may be used in logging messages

Method Detail

attemptReadData

public abstract T attemptReadData()
                           throws IOException

Performs the actual download. Implementations are encouraged to log query and details of success if applicable at the INFO level, but an error will be logged by the Downloader.

Returns:

downloaded data

Throws:

IOException

isComplete

public boolean isComplete()

Indicates whether the data has been downloaded. If this method returns true, then getData() will return the result.

Returns:

true iff download has completed, successfully or otherwise

getData

public T getData()

Immediately returns the downloaded data, or null if it has not been downloaded, or if a download has failed.

Returns:

data

clearData

public void clearData()

Resets the state of this downloader, as if no download attempt had been made.

setData

public void setData(T value)

Sets the state of this downloader as if it had just downloaded the given data item. This can be necessary to restore its state, since it affects the monitor component.

Parameters:

value - value that would have been downloaded

waitForData

public T waitForData()

Downloads the data if necessary, and returns its content. If a download attempt has already been completed, this will return immediately, otherwise it will block. If the download failed, null will be returned.

Returns:

data or null on failure

createMonitorComponent

public JComponent createMonitorComponent()

Returns a little component that monitors status of this downloader. Currently, it is blank before the download has happened, then turns to green on success or red on failure.

addActionListener

public void addActionListener(ActionListener listener)

Adds a listener that will be notified if the data acquisition status changes.

Parameters:

listener - listener

removeActionListener

public void removeActionListener(ActionListener listener)

Removes a previously added listener.

Parameters:

listener - listener