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            <div id=PageTitle>How to Use File Choosers</div>
            <blockquote>

File choosers provide a GUI for navigating the file system,
and then either choosing a file or directory from a list
or entering the name of a file or directory.
To display a file chooser, 
you usually use the <code>JFileChooser</code> API
to show a modal
<a href="dialog.html">dialog</a>
containing the file chooser.
Another way to present a file chooser is to add an instance of
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JFileChooser.html"><code>JFileChooser</code></a> to a container.

<p>

<blockquote><hr><strong>Note:</strong>&nbsp; If you intend to distribute your program as an unsigned
Java<font size="-2"><sup>TM</sup></font> Web Start application,
then instead of using the <code>JFileChooser</code> API
you should use the file services provided
by the JNLP API.
These services &#151;
<code>FileOpenService</code> and <code>FileSaveService</code> &#151;
not only provide support for choosing files in a restricted environment,
but also take care of actually opening and saving them.
An example of using these services is in
<a href="examples/index.html#JWSFileChooserDemo">JWSFileChooserDemo</a>.
Documentation for using the JNLP API is in the
<a class="TutorialLink" target="_top" href="../../deployment/webstart/index.html">Java Web Start</a> lesson.
<hr></blockquote>

<p>

The rest of this section discusses how to use 
the <code>JFileChooser</code> API.
A <code>JFileChooser</code> object
only presents the GUI for choosing files.
Your program is responsible for doing something
with the chosen file,
such as opening or saving it.
Refer to
<a class="TutorialLink" target="_top" href="../../essential/io/index.html">Basic I/O</a> for information on how to read and write files.

<p>
The <code>JFileChooser</code> API 
makes it easy to bring up open and save dialogs.
The look and feel determines what
these standard dialogs look like and how they differ.
In the Java look and feel,
the save dialog looks the same
as the open dialog,
except for the title on the dialog's window
and the text on the button that approves the operation.
Here is a picture of the Java look and feel's standard open dialog:

<p><center><IMG SRC="../../figures/uiswing/components/FileChooserOpenMetal.png" WIDTH="508" HEIGHT="360" ALIGN="BOTTOM" ALT="A standard open dialog shown in the Java look and feel"></center></p>
<p>
Here's a snapshot of an application 
that brings up an open dialog and a save dialog.

<p>

<p><center><IMG SRC="../../figures/uiswing/components/FileChooserDemo2Metal.png" WIDTH="272" HEIGHT="163" ALIGN="BOTTOM" ALT="A program that brings up an open or save dialog"></center></p><p>


<blockquote><hr><strong>Try this:</strong>&nbsp;
<ol>
<li> Compile and run 
     FileChooserDemo.
See the <a href="examples/index.html#FileChooserDemo" target="_top">examples index</a> for links to all the files required by this example.<li> Click the <strong>Open a File...</strong> button.
     Navigate around the file chooser, choose a file,
     and click the dialog's <strong>Open</strong> button.
<li> Use the <strong>Save a File...</strong> button
     to bring up a save dialog.
     Try to use all of the controls on the file chooser.
<li> In the source file 
<a class="SourceLink" target="_blank" href="examples/FileChooserDemo.java"><code>FileChooserDemo.java</code></a>,    change the file selection mode to directories-only mode.
     (Search for <code>DIRECTORIES_ONLY</code> and
     uncomment the line that contains it.)
     Then compile and run the example again.
     You'll only be able to see and select directories,
     not ordinary files.
</ol>
<hr></blockquote>

Bringing up a standard open dialog
requires only two lines of code:
<blockquote><pre>
//Create a file chooser
final JFileChooser fc = new JFileChooser();
...
<em>//In response to a button click:</em>
int returnVal = fc.showOpenDialog(<em>aComponent</em>);
</pre></blockquote>

The argument to the <code>showOpenDialog</code> method
specifies the parent component for the dialog.
The parent component affects the position of the dialog
and the frame that the dialog depends on.
For example, the Java look and feel places the dialog 
directly over the parent component.
If the parent component is in a frame,
then the dialog is dependent on that frame,
disappearing when the frame is iconified
and reappearing when the frame is deiconified.

<p>

By default,
a file chooser that hasn't been shown before
displays all files in the user's home directory.
You can specify the file chooser's initial directory
using one of <code>JFileChooser</code>'s other constructors,
or you can set the directory
with the <code>setCurrentDirectory</code> method.
<p>
The call to <code>showOpenDialog</code> appears in the
<code>actionPerformed</code> method of the <strong>Open a File...</strong>
button's action listener:
<blockquote><pre>
public void actionPerformed(ActionEvent e) {
    //Handle open button action.
    if (e.getSource() == openButton) {
        int returnVal = fc.showOpenDialog(FileChooserDemo.this);

        if (returnVal == JFileChooser.APPROVE_OPTION) {
            File file = fc.getSelectedFile();
            //This is where a real application would open the file.
            log.append("Opening: " + file.getName() + "." + newline);
        } else {
            log.append("Open command cancelled by user." + newline);
        }
   } ...
}
</pre></blockquote>

The <code>show<em>Xxx</em>Dialog</code>
methods return an integer
that indicates whether the user selected a file.
Depending on how you use a file chooser, 
it's often sufficient to check whether the return value is
<code>APPROVE_OPTION</code> 
and to do nothing for any other value.
To get the chosen file
(or directory, if you set up the file chooser
to allow directory selections),
call <code>getSelectedFile</code>
on the file chooser.
This method returns an instance of
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/io/File.html"><code>File</code></a>.
<p>
The example gets the name of the file and
uses it in the log message.
You can call other methods on the <code>File</code> object,
such as <code>getPath</code>,
<code>isDirectory</code>, or <code>exists</code>
to get information about the file.
You can also call other methods such as
<code>delete</code> and <code>rename</code>
to change the file in some way.
Of course, you might also want to open or save the
file using one of the reader or writer classes
provided by the Java platform.
See
<a class="TutorialLink" target="_top" href="../../essential/io/index.html">Basic I/O</a> for information about using readers and writers to
read and write data to the file system.

<p>
The example program uses the same
instance of <code>JFileChooser</code>
to display a standard save dialog.
This time the program calls <code>showSaveDialog</code>:
<blockquote><pre>
int returnVal = fc.showSaveDialog(FileChooserDemo.this);
</pre></blockquote>
By using the same file chooser instance to display
its open and save dialogs, the program reaps these benefits:
<ul>
<li> The chooser remembers the current directory between
     uses so the open and save versions automatically share the
     same current directory.
<li> You have to customize only one file chooser,
     and the customizations apply to both the open
     and save versions of it.
</ul>

Finally, the example program has commented-out lines of code
that let you change the file selection mode.
For example, the following line of code makes the file chooser
able to select only directories, and not files:

<blockquote><pre>
fc.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
</pre></blockquote>

Another possible selection mode is <code>FILES_AND_DIRECTORIES</code>.
The default is <code>FILES_ONLY</code>.
The following picture shows an open dialog 
with the file selection mode set to <code>DIRECTORIES_ONLY</code>.
Note that, in the Java look and feel at least, 
only directories are visible &#151; not files.

<p><center><IMG SRC="../../figures/uiswing/components/FileChooserDirectoriesMetal.png" WIDTH="508" HEIGHT="360" ALIGN="BOTTOM" ALT="A file chooser in DIRECTORIES_ONLY mode"></center></p>

<p>

If you want to create a file chooser
for a task other than opening or saving,
or if you want to customize the file chooser,
keep reading.
We'll discuss the following topics:

<ul>
<li> <a href="#advancedexample">Another Example: FileChooserDemo2</a>
<li> <a href="#customtask">Using a File Chooser for a Custom Task</a>
<li> <a href="#filters">Filtering the List of Files</a>
<li> <a href="#fileview">Customizing the File View</a>
<li> <a href="#accessory">Providing an Accessory Component</a>
<li> <a href="#api">The File Chooser API</a>
<li> <a href="#eg">Examples that Use File Choosers</a>
</ul>


<a name="advancedexample">
</blockquote>
<h3>Another Example: FileChooserDemo2</h3>
</a>
<blockquote>

Let's look at
<a href="examples/index.html#FileChooserDemo2">
<code>FileChooserDemo2</code></a>,
a modified version of the previous demo program that
uses more of the <code>JFileChooser</code> API.
This example uses a file chooser that has been
customized in several ways.
Like the original example, the user invokes
a file chooser with the push of a button.
Here's a picture of the file chooser:
 
<p><center><IMG SRC="../../figures/uiswing/components/FileChooserDemo3Metal.png" WIDTH="536" HEIGHT="360" ALIGN="BOTTOM" ALT="A file chooser with various customizations"></center></p><p>

<p>
As the figure shows, this file chooser
has been customized for a special task (Attach),
provides a user-choosable file filter (Just Images),
uses a special file view for image files,
and has an accessory component
that displays a thumbnail sketch of the currently selected
image file.

<p>
The remainder of this section shows you the code
that creates and customizes this file chooser.
See the <a href="examples/index.html#FileChooserDemo2" target="_top">examples index</a> for links to all the files required by this example.


</blockquote>
<a name="customtask">
<h3>Using a File Chooser for a Custom Task</h3>
</a>
<blockquote>
As you've seen, <code>JFileChooser</code>
provides <code>showOpenDialog</code> for displaying an open dialog
and <code>showSaveDialog</code> for displaying a save dialog.
<p>
The class has another method, <code>showDialog</code>,
for displaying a file chooser for a custom task in a dialog.
In the Java look and feel, the only difference between this dialog
and the other file chooser dialogs is the title on the dialog window
and the label on the approve button.
Here's the code from <code>FileChooserDemo2</code>
that brings up the file chooser dialog for the
<strong>Attach</strong> task:

<blockquote><pre>
JFileChooser fc = new JFileChooser();
int returnVal = fc.showDialog(FileChooserDemo2.this, "Attach");
</pre></blockquote>

The first argument to the <code>showDialog</code> method
is the parent component for the dialog.
The second argument is a <code>String</code> that
provides both the title for the dialog window
and the label for the approve button.
<p>
Once again, the file chooser doesn't do anything with
the selected file.
The program is responsible for implementing the custom task
for which the file chooser was created.
</blockquote>

<a name="filters">
<h3>Filtering the List of Files</h3>
</a>
<blockquote>
By default, a file chooser displays all of the files
and directories that it detects, except hidden files.
A program can apply one or more <em>file filters</em>
to a file chooser so that the chooser shows only some files.
The file chooser calls the filter's <code>accept</code> method
for each file to determine whether it should be displayed.
A file filter accepts or rejects a file based
on some criteria such as file type, size, ownership, and so on.
Filters affect the list of files displayed by the file chooser.
The user can enter the name of any file even if it's not displayed.