Swing Hacks

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Chapter 4, File Choosers

#32 Preview ZIP and JAR Files

HACK

Before you read any further, I want to warn you that this is

one of the longest and most complicated hacks in the book. I

don’t want to scare you away, but the code is pretty dense.

Of course, you wouldn’t expect any less from a hacks book,

right? What you will learn from this hack, however, will let

you build custom filesystem views for any type of data-

source, including FTP, WebDAV, or even SQL databases. I

think the complexity is worth it. Plus, you’ll learn more about

how the

File object really works and how to hack it to pieces.

Build File Proxies

The JFileChooser uses a FileSystemView to access the real filesystem. This

view, unfortunately, assumes the existence of actual

java.io.File objects.

There is no way to represent a filesystem without

Files, which wouldn’t be a

problem except that

File is a real class with many methods, not a simple

interface. Fortunately,

File is not declared final. You can override each

method with your own version to redirect the calls to another object, and

that’s exactly how this hack works. By creating proxies around the real ZIP

file objects, you can fool the

FileSystemView into working with items that

aren’t real files.

ZIP files are represented in the

java.util.zip package by a ZipFile object

that contains one

ZipEntry for each compressed file it contains. To show the

compressed files in the chooser, each ...