Java: Create a File Object from URL (without downloading)

http://java.sun.com/javase/6/docs/api/java/net/URL.html#getFile()

that returns a string - not a File Object

http://java.sun.com/j2se/1.4.2/docs/api/java/net/URL.html

File is a reference of the resource in the local file system and URL is a reference of a resource in remote or local system. So you will be able to create URL from File but the reverse is not possible unless you write the URL resource locally and then create File reference of it!

Thanks for the clarification ksivanath.

So, if i have an *applet* running on www.whatever.com, trying to create a File object from www.whatever.com/images/thisImage.jpg - this isn't possible?

>>that returns a string - not a File Object

Well only a String is meaningful. The file(File) resides elsewhere.

What is your objective?

nope, u need to write that locally and then refer it as File!

locally  --> local disk!

>>trying to create a File object from ...

Why do you *want* to create a File object?

Also

>>So, if i have an *applet* running on www.whatever.com

the applet won't be running there (probably). The applet runs on the machine of whomever's looking at it

CEHJ:

Objective: Metaphile (http://sourceforge.net/projects/metaphile) is a Java package that basically reads metadata from image files.  It requires a File object.  I want to use it in a web-based environment, in an applet.  All images are "local" - local to the server where the applet was launched.  like i wrote earlier, if the applet is running on www.whatever.com, all images are in www.whatever.com/images.  I need to pass it a File object from within an applet . . .

CEHJ:

(sorry, you're right, the applet isn't "running on" www.whatever.com - it was launched from there (or whatever the appropriate vocabulary is).  anyway, the project involves reading metadata, using metaphile, in an applet environment.)

Reading metadata from a remote URL is a piece of cake if that's what you want to do...

... and you can do that without using a file e.g.

InputStream metaDataIn = getClass().getResourceAsStream("metadata.xml");

                                              

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>>getClass().getResourceAsStream("metadata.xml");

CEHJ, I think, the asker is using a openesourced java called metafile which reads metadata from image file if you pass the image as File instasnce to them... in such case, this is not appropriate. your code will be useful if he has a file in the jar and want to read!

the metadata is embedded in the image . . . does that make a difference?  i've attached a file if you'd like to try.  the XMP metadata is as follows:

- CopyrightNotice: 2006
- Keywords: book, Senior Library 2006, bird, orange
- Document Title: To Kill a Mockingbird
- Author: Richard Smith
- Description: To Kill a Mockingbird book cover

Just get the stream as i mentioned and you'll be able to get the contents, including this sort of stuff:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>com.apple.print.PageFormat.PMHorizontalRes</key>
................................................

                                              

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if you dl the image and open it in photoshop you get something like the attached image.  getting at this data is no simple task, hence rather robust libraries like metaphile.  all images in www.whatever.com/images contain embedded metadata, which i need to access through an applet . . . and metaphile only takes File objects . . .

>>and metaphile only takes File objects

Unfortunate and bad design. Do you have a link to this API?

Sourceforge project: http://sourceforge.net/projects/metaphile

code examples: http://www.miniturismo.co.uk/metaphile/example01.php
     - also see (on the same site) example02.php, example03.php, example04.php, example05.php

Since they haven't seen fit to give you an InputStream ctor, you'll have to create a temporary file. Web Start would be less strict than an applet.

If you can get hold of the source (can't see it there) you can fix it easily enough. Or get them to do it ;-)

whats the problem for you to write the file locally from applet?

from http://java.sun.com/sfaq/#read

unless i'm missing something:

What are applets prevented from doing?
In general, applets loaded over the net are prevented from reading and writing files on the client file system, and from making network connections except to the originating host.

How do I let an applet write a file?
Applets loaded into a Java-enabled browser can't write files.

I suppose all this prevents me from getting access to a File object . . .

all you have to sign the applet jar files and the client user has to accept the certificate while running the applet!

here is how you sign the applet,

http://www.doc.ic.ac.uk/csg/java/signed-applets/

here is a complete glossary of signed applet...

http://mindprod.com/jgloss/signedapplets.html

CEHJ:

i've managed to track down the source in a CVS repository off sourceforge.  here's the constructor i'd need to change - any ideas?

public JpegFile(File f) throws IOException, JpegException {
        try {
            this.file = f;

            fileLog.log(Level.INFO, "Creating JpegFile based on file " + f.getAbsolutePath());

            fileStream = new BufferedInputStream(new FileInputStream(file));
            this.loadHeader();
        } finally {
            if (fileStream != null) {
                fileStream.close();
            }
        }
    }

and call,

new JpegFile( url.openStream() ) ;

Yes, but put an appropriate loggin line in there too