Talk:Calling Java from JRuby

From JRubyWiki

How about if someone creates a Calling Ruby from Java? That content is listed under Java Integration

More info on calling third party classes?

Ok. I'm live now. The system let me create a comment before I confirmed my account email, but silently failed when I tried to post it.

So here's my comment: Will we see additional information on accessing 3rd party classes? I have a number of notes on the subject, but I'm having a hard time with the large number of test permutations. Here's what I have so far (all of it subject to change):

   1. Put the JAR files in the CLASSPATH
      (but this may be irrelevant. See step 2)
      -or-
      put them in $RUBY_HOME/lib (haven't tried this)
      -or-
      for NetBeans on windows, in JRUBY_EXTRA_CLASSPATH

AND 2. Require each jar by name, specifying the full path

      !-The full path is required, even when in the CLASSPATH

      So this works:
        require "/some/path/MyStuff.jar" 
      But not this:
        require "MyStuff.jar" 
      It fails with "no such file to load". That behavior must
      be considered a bug. (The whole idea of the CLASSPATH is 
      to isolate the code from path changes)

      ! With the full path specified in the require statement,
        it seems to work, _whether or not_ the CLASSPATH is set.
      --the CLASSPATH does not seem to be accessed when set via
        the CSH setenv function
      --that would explain why the full path is needed
     

AND 3. Do an include_class on each class I want to access,

      use a fully qualified package name.
      -or-
      Using the Java:: prefix the fully qualified package
      name when naming one of classes in the code.

  So if this method returns a Foo object:
     x = Java::some.package.MyClass.staticGetMethod()

  then:
     include_class is /not/ necessary for MyClass
     include_class /is/ necessary for Foo

Note:

  Doing an optional include_class on some.package.MyClass
  does /not/ let you use a shorthand reference like Java::MyClass
  in the code. You still need the fully qualified package
  name (Java::some.package.MyClass)

$CLASSPATH

I have found that adding a jar to the $CLASSPATH from within a jruby script will give me access to the classes in it.

$CLASSPATH.append '/path/to/jar.jar'
MC = Java::ComMypackage::MyClassFromJarFile

But $CLASSPATH is a weird variable. The append method isn't on other arrays, and many array methods are not on $CLASSPATH. It must be an anonymous class for all I can tell.

-- Yes, $CLASSPATH is a special variable that modifies the classloading logic. It's not quite a normal array, so we can be notified when elements are appended to it and update accordingly. Headius

JRuby Applet ?

Could you provide an example Hello World applet in JRuby? thank you.