Swing Hacks

Code Models That Don’t Block #93

Chapter 12, Miscellany

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469

HACK

In this case, all the loading is done in a

run( )

method, so the constructor

simply creates a

Thread

called

readThread

to wrap the

run( )

, starts the thread,

and then returns, freeing up the event-dispatch thread almost immediately.

So, now it’s up to

readThread to read the stream and load its contents into

the

Document. As in the blocking version (Example 12-9), it reads bytes into a

buffer, but instead of building a big

StringBuffer with which to do a mass-

insert, it uses

Document’s insertString( ) method to put each bufferful into

the document. Since

insertString( ) will cause the model to fire off events,

this will provide for a constant updating of the view; that’s why this version

calls

insertString( ) each time through the loop instead of once at the bot-

tom, as the blocking version did. However,

insertString( ) is a Swing

method, meaning it’s thread-unsafe, so you can’t call it directly from the

readThread. Instead, you set up a worker and use SwingUtilities.

invokeLater( )

to put the insertString( ) call, and only that call, back onto

the event-dispatch thread.

Running the Code

If you have a fast Internet connection, it is possible that you’ll load the data

so fast that you don’t mind the blocking or you can’t see the incremental

updating of the non-blocking version. To make this more dramatic, increase

the time that each model

sleep( )s, and reduce the size of the buffer used to

read bytes from the

InputStream. To show the incremental, non-blocking

update in Figure 12-8, I set the

sleep( ) time to 500 milliseconds and the

buffer size to a mere 80 bytes.

Now you have a URL-loading document and a model for

JTextComponents

that will handle its own threaded loading and can thus be dropped into any

JTextComponent without needing to add any other code to manage its

threaded operation.

public boolean isAlive( ) {

return (readThread != null) && (readThread.isAlive( ));

}

public float getProgress( ) {

return (float) totalBytesRead/length;

}

}

Example 12-10. Document that will not block on URL loading (continued)