尝试在浏览器上打开applet时出现错误事件

Question

I have done a few Java programs but this is the first one that I'm trying to run as an applet so I might have some basic error.

I compiled all the classes and put them together in a jar file called final. I followed a few tutorials to make a JNLP file that I called jnlp (yeah, I know, I'm very original:) and on which I called to my jar file and I called the JNLP file from an HTML file.

Those are the last lines of the java console output: (before them, the console is filled with my JNLP file)

at sun.plugin2.applet.JNLP2Manager.loadJarFiles(Unknown Source)
    at sun.plugin2.applet.Plugin2Manager$AppletExecutionRunnable.run(Unknown Source)
    at java.lang.Thread.run(Unknown Source)
preloader: Added pending event 2: ErrorEvent[url=null label=JNLP not an applet, nor a JavaFX application cause=JNLP not an applet, nor a JavaFX application

Here is the JNLP file:

<?xml version="1.0" encoding="UTF-8"?>
<jnlp spec="1.0+" codebase="" href="jnlp.jnlp">
    <information>
        <title>Encryption Software</title>
        <vendor>Atlantis Atlantis</vendor>
        <icon href="encrypt_logo.jpg"/>
        <offline-allowed/>
    </information>
    <resources>
        <!-- Application Resources -->
        <j2se version="1.6+" href=
           "http://java.sun.com/products/autodl/j2se"/>
        <jar href="final.jar"
            main="true" />

    </resources>
    <application-desc
         name="Encryption Software"
         main-class="EncryptApplication"
         width="500"
         height="300">
     </application-desc>
     <update check="background"/>
</jnlp>

Here is the JS used to launch the applet:

<script src="https://www.java.com/js/deployJava.js"></script>
<script>
    var attributes = {code:'', width:500, height:500};
    var parameters = {jnlp_href: 'jnlp.jnlp'};
    deployJava.runApplet(attributes, parameters, '1.6');
</script>

Answer 1

Is the EncryptionApplication really an applet? To be an applet it must extend Applet or JApplet .

If it is not an applet, it cannot be embedded in HTML.

If it is an applet, the JNLP must declare it as such, so:

    <application-desc
         name="Encryption Software"
         main-class="EncryptApplication"
         width="500"
         height="300">
     </application-desc>

Should be:

    <applet-desc
         name="Encryption Software"
         main-class="EncryptApplication"
         width="500"
         height="300">
     </applet-desc>

Tips

• Be sure to check the JNLP using JaNeLA .
• Avoid applets like you might avoid the plague. They were always a complete PITA and with recent security updates, have only become more so. See Why CS teachers should stop teaching Java applets for my take on the matter.
• It is possible to launch an application (eg a JFrame based app.) from a link using Java Web Start . They will be subject to the same (very strict) security requirements of applets, but have none of the applet specific problems (see link in previous point for details).
• As mentioned by @ElliottFrisch, it is best to include a valid value for the code attribute. There are circumstances in which it can be left out, but I won't get into that right now..