applet.html

jsf、swing的官方指南

<li> You set the layout manager on a Swing applet's content pane,
     not directly on the applet.
<li> The default layout manager for a Swing applet's content pane is
     <code>BorderLayout</code>.
     This differs from the default layout manager for
     <code>Applet</code>, which is <code>FlowLayout</code>.
<li> You should not put painting code directly in a <code>JApplet</code>
     object.
     See 
<a class="TutorialLink" target="_top" href="../painting/index.html">Performing Custom Painting</a>     for examples of how to perform custom painting in applets.
</ul>


</blockquote>
<h3>
<a name="thread">Threads in Applets</a>
</h3>
<blockquote>
Swing components should be created, queried, and manipulated
on the event-dispatching thread,
but browsers don't invoke applet "milestone" methods
from that thread.
For this reason,
the milestone methods &#151;
<code>init</code>,
<code>start</code>,
<code>stop</code>,
and <code>destroy</code> &#151;
should use the <code>SwingUtilities</code> method
<code>invokeAndWait</code>
(or, if appropriate, <code>invokeLater</code>)
so that code that refers to the Swing components
is executed on the event-dispatching thread.
More information about these methods and the event-dispatching thread
is in 
<a class="TutorialLink" target="_top" href="../concurrency/index.html">Concurrency in Swing</a>.


<p>
Here is an example of an <code>init</code> method:

<blockquote><pre>
public void init() {
    //Execute a job on the event-dispatching thread:
    //creating this applet's GUI.
    try {
        javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                createGUI();
            }
        });
    } catch (Exception e) {
        System.err.println("createGUI didn't successfully complete");
    }
}

private void createGUI() {
    JLabel label = new JLabel(
                       "You are successfully running a Swing applet!");
    label.setHorizontalAlignment(JLabel.CENTER);
    label.setBorder(BorderFactory.createMatteBorder(1,1,1,1,Color.black));
    getContentPane().add(label, BorderLayout.CENTER);
}
</pre></blockquote>


<p>
The <code>invokeLater</code> method 
is not appropriate for this implementation
because it allows <code>init</code>
to return before initialization is complete,
which can cause applet problems
that are difficult to debug.

<p>
The <code>init</code> method in <code>TumbleItem</code>
is more complex, 
as the
following code shows.
Like the first example, 
this <code>init</code> method implementation
uses <code>SwingUtilities.invokeAndWait</code>
to execute the GUI creation code 
on the event-dispatching thread.
This <code>init</code> method
sets up a
<a class="TutorialLink" target="_top" href="../misc/timer.html">Swing timer</a>to fire action events the update the animation.
Also, <code>init</code> uses
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/SwingWorker.html"><code>javax.swing.SwingWorker</code></a> to create a background task
that loads the animation image files,
letting the applet present a GUI
right away, without waiting for all resources to be loaded.

<blockquote><pre>
private void createGUI() {
    ...
    animator = new Animator();
    animator.setOpaque(true);
    animator.setBackground(Color.white);
    setContentPane(animator);
    ...
}

public void init() {
    loadAppletParameters();

    //Execute a job on the event-dispatching thread:
    //creating this applet's GUI.
    try {
        <b>javax.swing.SwingUtilities.invokeAndWait(new Runnable() {
            public void run() {
                createGUI();
            }
        });</b>
    } catch (Exception e) { 
        System.err.println("createGUI didn't successfully complete");
    }

    //Set up the timer that will perform the animation.
    timer = new javax.swing.Timer(speed, this);
    timer.setInitialDelay(pause);
    timer.setCoalesce(false);
    timer.start(); //Start the animation.

    //Background task for loading images.
    SwingWorker worker = (new SwingWorker<ImageIcon[], Object>() {
            public ImageIcon[] doInBackground() {
                final ImageIcon[] innerImgs = new ImageIcon[nimgs];
            <em>...//Load all the images...</em>
            return imgs;
        }
        public void done() {
            //Remove the "Loading images" label.
            animator.removeAll();
            loopslot = -1;
            try {
                imgs = get();
            } <em>...//Handle possible exceptions</em>
        }

    }).execute();
}
</pre></blockquote>

<p>
You can find the applet's source code in
<a class="SourceLink" target="_blank" href="examples/TumbleItem.java"><code>TumbleItem.java</code></a>.
To find all the files required for the applet,
including a link to a JNLP file
that lets you run it using Java Web Start, see the
<a href="examples/index.html#TumbleItem">example index</a>.


</blockquote>
<h3>
<a name="images">Using Images in a Swing Applet</a>
</h3>
<blockquote>
The <code>Applet</code> class provides the
<code>getImage</code> method for
loading images into an applet.
The <code>getImage</code> method creates
and returns an <code>Image</code> object
that represents the loaded image.
Because Swing components use <code>Icon</code>s
rather than <code>Image</code>s to refer to pictures,
Swing applets tend not to use <code>getImage</code>.
Instead Swing applets create instances of
<code>ImageIcon</code> &#151; an icon loaded from an image file.
<code>ImageIcon</code> comes with a code-saving benefit:
it handles image tracking automatically.
Refer to 
<a class="TutorialLink" target="_top" href="../components/icon.html">How to Use Icons</a> for more information.

<p>
The animation of Duke doing cartwheels
requires 17 different pictures.
The applet uses one <code>ImageIcon</code> per picture
and loads them in its <code>init</code> method.
Because images can take a long time to load,
the icons are loaded in a separate thread
implemented by a <code>SwingWorker</code> object.
Here's the code:

<blockquote><pre>
public void init() {
    ...
    imgs = new ImageIcon[nimgs];
    (new SwingWorker<ImageIcon[], Object>() {
        public ImageIcon[] doInBackground() {
            //Images are numbered 1 to nimgs,
            //but fill array from 0 to nimgs-1.
            for (int i = 0; i &lt; nimgs; i++) {
                imgs[i] = loadImage(i+1);
            }
            return imgs;
        }
        ...
    }).execute();

}
...
protected ImageIcon loadImage(int imageNum) {
    String path = dir + "/T" + imageNum + ".gif";
    int MAX_IMAGE_SIZE = 2400;  //Change this to the size of
                                 //your biggest image, in bytes.
    int count = 0;
    BufferedInputStream imgStream = new BufferedInputStream(
       this.getClass().getResourceAsStream(path));
    if (imgStream != null) {
        byte buf[] = new byte[MAX_IMAGE_SIZE];
        try {
            count = imgStream.read(buf);
            imgStream.close();
        } catch (java.io.IOException ioe) {
            System.err.println("Couldn't read stream from file: " + path);
            return null;
        }
        if (count &lt;= 0) {
            System.err.println("Empty file: " + path);
            return null;
        }
        return new ImageIcon(Toolkit.getDefaultToolkit().createImage(buf));
    } else {
        System.err.println("Couldn't find file: " + path);
        return null;
    }
}
</pre></blockquote>

The <code>loadImage</code> method
loads the image for the specified frame of animation.
It uses
the <code>getResourceAsStream</code> method
rather than the usual <code>getResource</code> method
to get the images.
The resulting code isn't pretty,
but <code>getResourceAsStream</code>
is more efficient than <code>getResource</code>
for loading images from JAR files into applets that are executed
using Java Plug-in<sup><font size=-2>TM</font></sup> software.
For further details, see
<a class="TutorialLink" target="_top" href="../components/icon.html#applet">Loading Images Into Applets</a>.

</blockquote>
<h3>
<a name="plugin">Embedding an Applet in an HTML Page</a>
</h3>
<blockquote>

The recommended way to include an applet in an HTML page is
using the APPLET tag.
Here's the APPLET tag for the cartwheeling Duke applet:

<blockquote><pre>
&lt;applet code="TumbleItem.class" 
        codebase="examples/"
        archive="tumbleClasses.jar, tumbleImages.jar"
        width="600" height="95"&gt;
    &lt;param name="maxwidth" value="120"&gt;
    &lt;param name="nimgs" value="17"&gt;
    &lt;param name="offset" value="-57"&gt;
    &lt;param name="img" value="images/tumble"&gt;

Your browser is completely ignoring the &amp;lt;APPLET&amp;gt; tag!
&lt;/applet>
</pre></blockquote>

To find out about the various &lt;APPLET&gt; tag parameters, refer to
<a class="TutorialLink" target="_top" href="../../deployment/applet/applettag.html">Using the applet Tag</a> and 
<a class="TutorialLink" target="_top" href="../../deployment/applet/html.html">Using the APPLET Tag	</a>.


</blockquote>
<h3>
<a name="api">The JApplet API</a>
</h3>
<blockquote>
The next table lists the interesting methods
that <code>JApplet</code> adds to the applet API.
They give you access to features provided by the root pane.
Other methods you might use are defined by the
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/awt/Component.html"><code>Component</code></a> and
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/java/applet/Applet.html"><code>Applet</code></a> classes.
See <a href="jcomponent.html#complookapi">Component Methods</a>
for a list of commonly used <code>Component</code> methods,
and
<a class="TutorialLink" target="_top" href="../../deployment/applet/index.html">Applets</a> for help in using <code>Applet</code> methods.

<p>

<table border=1>
<tr>
<th align=left>Method
</th>
<th align=left>Purpose

</th>
</tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#setContentPane(java.awt.Container)">void setContentPane(Container)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#getContentPane()">Container getContentPane()</a>    </td>
    <td>Set or get the applet's content pane.
        The content pane contains the applet's visible GUI components
        and should be opaque.

    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#createRootPane()">JRootPane createRootPane()</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#setRootPane(javax.swing.JRootPane)">void setRootPane(JRootPane)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#getRootPane()">JRootPane getRootPane()</a>    </td>
    <td>Create, set, or get the applet's root pane. The root pane
        manages the interior of the applet including the content pane,
        the glass pane, and so on.
 
    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#setJMenuBar(javax.swing.JMenuBar)">void setJMenuBar(JMenuBar)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#getJMenuBar()">JMenuBar getJMenuBar()</a>    </td>
    <td>Set or get the applet's menu bar
        to manage a set of menus for the applet.
 
    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#setGlassPane(java.awt.Component)">void setGlassPane(Component)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#getGlassPane()">Component getGlassPane()</a>    </td>
    <td>Set or get the applet's glass pane.
        You can use the glass pane to intercept mouse events.

    </td>
  </tr>
  <tr>
    <td>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#setLayeredPane(javax.swing.JLayeredPane)">void setLayeredPane(JLayeredPane)</a>    <br>
<a class="APILink" target="_blank" href="http://java.sun.com/javase/6/docs/api/javax/swing/JApplet.html#getLayeredPane()">JLayeredPane getLayeredPane()</a>    </td>
    <td>Set or get the applet's layered pane.
        You can use the applet's layered pane to put components on top of
        or behind other components.
    </td>
  </tr>
</table>

</blockquote>

<h3>
<a name="eg">Applet Examples</a>
</h3>
<blockquote>
This table shows examples of Swing applets
and where those examples are described.

<p>
<table>
<tr>
<th align=left> Example
</th>
<th align=left> Where Described
</th>
<th align=left> Notes
</th>
</tr>

<tr>
<td> <a href="examples/index.html#TumbleItem">
     <code>TumbleItem</code></a>
</td>
<td> This page
</td>
<td> An animation applet
</td>
</tr>

<tr>
<td> <a href="../components/examples/index.html#IconDemoApplet">
     <code>IconDemoApplet</code></a>
</td>
<td> 
<a class="TutorialLink" target="_top" href="../components/icon.html">How to Use Icons</a></td>
<td> An applet for showing photos.
</td>
</tr>

</table>



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