Re: [Jython-users] idea: custom tag library and jython

[Niko S. <ni...@na...>]

Ashish,

> How about developing a custom tag for web apps. One that takes
> jython scriplet in its body. The request, response, session etc
> would be available as explicit objects. The tag could embed a
> jython interpreter and execute the given code. How I wish jsp 
> were jython server pages!

very interesting you are mentioning this idea, i was thinking in 
the same lines just a few days ago (and didn't come back). But 
through your posting i just tried it out today: and it turns out 
that it is possible :) (even if it is a bit more extra effort):

creating just a straight forward jython class inherited from 
javax.servlet.jsp.tagext.TagSupport gave me a strange error 
message: "AttributeError: write-only attr: pageContext". Also with 
setting python.security.respectJavaAccessibility to false didn't 
help, so i had to write a Java class (derived from TagSupport) 
which provides an accessor method to pageContext. The Jython Custom 
Tag implementation has then to use this to get access to the 
PageContext object.

---- DemoTag.py ----
from java.io import IOException
from javax.servlet.jsp import JspTagException
from niko.test import JythonTagSupport

class DemoTag(JythonTagSupport):
    
    def doStartTag(self):
        try:
            out = self.pageContext.getOut()
            out.print("Hello World from Jython Tag.")
        except IOException, e:
            raise JspTagException("Input/output error: %s" % 
e.toString())
        # since this is an empty tag
        return self.SKIP_BODY

---- JythonTagSupport ----
package niko.test;

import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.TagSupport;

public class JythonTagSupport extends TagSupport {

  public JythonTagSupport() {
    super();
  }

  public PageContext getPageContext() {
    return pageContext;
  }
  
}
-----

Then the only two remaining steps are to define the new jython tag 
in your tag library descriptor file (TLD) and make sure that 
jython.jar is available to the classloader of your servlet 
container.

Happy jython-custom-tag-developing :-)
Niko