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Friday Jan 19, 2007

Scripting with servlets [jacl] - part V (Sun Java System WebServer 7.0)

Scripting with servlets [jacl]  - part V  (Sun Java System WebServer 7.0)
 

About the language

Jacl is the implementation of TCL over jvm. It supports interaction with the java objects
using the same command notation. While originally a procedural language, extensions like
incrTcl can be used provide object orientation to the language.

JaclServlet

The ScriptServlet developed in the previous entry is used here as the parent class.
 

package com.sun.servlet;

import java.io.*;
import java.util.*;
import tcl.lang.*;

import javax.servlet.http.*;

public class JaclServlet extends ScriptServlet {

    public static Interp jt = new Interp();

    public void initialize(String handler, Object code) throws Exception {
        jt.setVar("httpservlet",ReflectObject.newInstance(jt, JaclServlet.class, this),
              TCL.GLOBAL_ONLY);
        jt.eval((String)code);
    }

    public void eval(Object fn, HttpServletRequest request, HttpServletResponse response) {
        try {
            jt.setVar("request",ReflectObject.newInstance(jt, HttpServletRequest.class, request),
                  TCL.NAMESPACE_ONLY);
            jt.setVar("response",ReflectObject.newInstance(jt, HttpServletResponse.class, response),
                  TCL.NAMESPACE_ONLY);
            jt.eval((String)fn);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

 

Providing the handler

Jvm Bindings.

The Java objects are treated as commands with in jacl, allowing to interact with them by
using parameters instead of method names. It also provides convenience commands to access
fields, create new objects, calling static methods etc.

ie:  System.out.println("mystring") is written as [java::field System out] println "Mystring"

docroot/WEB-INF/code/jacl.tcl

package require java

set do_get {
    set out [$response getWriter]
    $response setContentType {text/html}
    set spath [$request getServletPath]
    set filename [[[$httpservlet getServletConfig] getServletContext] getRealPath $spath]
    set e [catch {eval [[$httpservlet read $filename] toString]} o]
    if {$e == 1} {
        $out println "<html><body><h1> ServletError ($o)</h1><xmp>"
        $out println $errorInfo
        $out println {</xmp><body></html>}
    } else {
        $out println $o
    }
}

$httpservlet add get $do_get
$httpservlet add post $do_get


The current instance of ScriptServlet is available as the variable 'httpservlet' inside the script. Since jacl
does not have the concept of lexical closures, we are stuck with binding to a variable of our choice, rather than
allow the end user to specify it in jacl.
Due tothe same reason, rather than setting the symbols 'get' and 'post' to executable functions, we associate
them with just strings containing scripts to execute.

An example js script that can get executed:

/docroot/hello.tcl

set at [[java::new java.util.Date] toString]
set from [$request getServletPath]
return "<html> <head><title>abc</title></head> <body> <h1> Hello at $at from $from </h1> </body> </html>"

Build  Steps.

          The complete jacl-webapp can be downloaded here. Extract the contents to a directory called 'jacl'
inside samples in your installation (samples/java/webapps/jacl). It has to be in that directory to make use
of the common.xml during ant build.

Update the js.jar if required. 

Your extracted directory will look like this.

|cd jacl
|find .
./docs
./docs/index.html
./src
./src/build.xml
./src/JaclServlet.java
./src/docroot
./src/docroot/WEB-INF
./src/docroot/WEB-INF/lib
./src/docroot/WEB-INF/lib/jacl.jar
./src/docroot/WEB-INF/lib/tcljava.jar
./src/docroot/WEB-INF/web.xml
./src/docroot/WEB-INF/sun-web.xml
./src/docroot/WEB-INF/code
./src/docroot/WEB-INF/code/jacl.tcl
./src/docroot/index.html
./src/docroot/hello.tcl
./src/ScriptServlet.java
./deploy.tcl

Please note that the jacl used here is 1.3.3 which is superseeded by Jacl 1.4. If you are using Jacl 1.4, then the number of jars
are more. Make sure that you have all the jars from the Jacl 1.4 distribution in your lib directory.

The jacl-webapp.war will be created in the jacl directory when you run ant from inside
the src. This war file can be deployed on the webserver using the wadm.

wadm  -u admin -f deploy.tcl

 Once the deployment goes through, you will be able to access the js file using the url

http://yourserver:port/jacl/hello.tcl 


Posted at 12:43AM Jan 19, 2007 by Rahul Gopinathan Nair in scripting  |  Comments[3]

Comments:

Someone recently pointed out this article - nice. I would also like to point out my current project, Aejaks. Aejaks brings Tcl and Tk scripting to web programming. Aejaks uses a Jacl interpreter on top of the Echo2 system. Aejaks ships with Jetty (doooh!) but the WAR file should easily be dropped into the Sun Java Webserver. Also, nice job on using Jacl to script the Sun Webserver!!

Posted by Tom Poindexter on July 31, 2007 at 09:09 AM IST #

Oops, the Aejaks website didn't print with my comment. Here it is: http://aejaks.sf.net

Posted by Tom Poindexter on July 31, 2007 at 09:16 AM IST #

Aejaks is cool. It certainly helps to bring the tcl/tk GUI to the www world.
Hope your project receive more attention.

Posted by rahul on August 19, 2007 at 08:19 PM IST #

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