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Dev : Extensions : Example Code : Calling Java from Javascript

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</pre> </pre>
http://www.xulplanet.com/references/xpcomref/ifaces/nsIJVMManager.html#method_showJavaConsole http://www.xulplanet.com/references/xpcomref/ifaces/nsIJVMManager.html#method_showJavaConsole
 +
 +
 +Here's the code I use to log exceptions. getStackTrace doesn't always work. I haven't figured out why, so I do it last, wrap it in a try catch, and print out my own "rough" stack trace first. (No line numbers.)
 +Wrap all java calls in a try catch and log the exception. Mozilla doesn't always report them and when it does it doesn't give the stack trace, and it's usually wrapped in a meaningless exception.
 +<pre>
 +function logExc(e) {
 + try {
 + while(e != null) {
 + debug(e);
 + e = e.getCause();
 + }
 + debug(netscape.javascript.JSUtil.getStackTrace(e));
 + } catch(exp) {
 + debug("exception while logging exception");
 + debug(exp);
 + debug("exception being logged");
 + debug(e);
 + }
 +}
 +</pre>

Revision as of 23:19, 26 October 2005

This page is currently notes of what I had to do to call Java from Javascript.

Here's an example from a blog: http://mozilla-firefox-extension-dev.blogspot.com/2004/11/calling-java-code-in-custom-jars-from.html

   var cl = new Packages.java.net.URLClassLoader(
       [
           new Packages.java.net.URL(
               'http://foo.net/bar.jar')
       ]
   );

   var aClass = Packages.java.lang.Class.forName("HelloWorld", true, cl);
   var aStaticMethod = aClass.getMethod("getGreeting", []);
   var greeting = aStaticMethod.invoke(null, []);
   alert(greeting);


In order to write to the file system, I had to add this to the javascript code: java.lang.System.setSecurityManager(null); I could read a jar from the filesystem without a problem.

Calling showJavaConsole is very useful for debugging:

        var jvm = Components.classes["@mozilla.org/oji/jvm-mgr;1"].getService(Components.interfaces.nsIJVMManager);
	jvm.showJavaConsole();

http://www.xulplanet.com/references/xpcomref/ifaces/nsIJVMManager.html#method_showJavaConsole


Here's the code I use to log exceptions. getStackTrace doesn't always work. I haven't figured out why, so I do it last, wrap it in a try catch, and print out my own "rough" stack trace first. (No line numbers.) Wrap all java calls in a try catch and log the exception. Mozilla doesn't always report them and when it does it doesn't give the stack trace, and it's usually wrapped in a meaningless exception.

function logExc(e) {
    try {
        while(e != null) {
            debug(e);
            e = e.getCause();
        }
        debug(netscape.javascript.JSUtil.getStackTrace(e));
    } catch(exp) {
        debug("exception while logging exception");
        debug(exp);
        debug("exception being logged");
        debug(e);
    }
}