类文件中的魔术值21877456不兼容

Question

Im trying to use java applet on my web page. I try/search lots of thing but no chance. So here is the case.

My applet code is simple in app.html :

    <applet codebase="." archive="applet.jar" code="de.escape.quincunx.dxf.apViewer" width="640" height="480" name="TEST">
    <param name="file"               value="40.dxf">
    <param name="framed"             value="false">
    <param name="frameWidth"         value="800">
    <param name="frameHeight"        value="600">
    </applet>

This html file is working when i directly open in browser. Its working when i serve it with apache but its not working and give error "Incompatible magic value 21877456 in class file" when i try to serve with IIS. In apache i try php and html, both is working.

Is there any special configuration need on IIS when i try to serve applet?

Thank you for your answers.

Answer 1

I think IIS is not serving the right file for a .class, probably it is returning a 404 error or something similar, since it cannot find the file.

That error means that Java was expecting a .class file, all class files start with 0xCAFEBABE, which is a magic number with which Java can check that the file it is receiving is in fact a class file. In your case, however, the file returned by IIS is not a class file, it does not start with 0xCAFEBABE, and Java is unable to parse it.

The most common reason for it is that the web server is not able to serve the file, often because of a 404 error.

You should check what happens under the hood, search in IIS logs for requests of .class files, or use a tool (maybe even firebug) to see what is returned to the browser.

Answer 2

Finally i found a solution. Actually its not the exact solution but thank you for your answer Simone Gianni. His answer lead me to deeply search in IIS access logs and compare them with APACHE access logs. And yes, both was same and looks like couple of classes are not in place in the JAR file. So apVPORT.class is not in the jar file and developer who wrote this applet leave the calls for those classes in the other part of applet even he is not using them.

If someone can answer the reason why apache don't send any information or "its okey" information to java and continue loading rest of the applet even it see the 404 for apVPORT.class but IIS send 404 to java, this will be the final answer for this question.

Answer 3

Incompatible magic value 21877456 in class file : I found that this error comes when page is not able to reach /read the jar file.

in aspx page -

   <applet code="FileAccess.class"
   archive="../applet/SignFileAccessApplet.jar" width="325" height="325">  
   </applet>

in archive check whether url is proper or not by using "pickurl" option provided by intellisense of Visual Studio. class file path in jar file need to be given in code attribute.