Welcome to Helma!

Hannes Wallnöfer

Michael Platzer

This work is licensed under a Creative Commons Attribution 3.0 Unported License.

What is Helma?

Helma is a scriptable, open-source
Java Web Application Server

res.write("Hello " + java.net.InetAddress.getLocalHost());

Helma is written in Java and employs Javascript for its server-side scripting environment, removing the need for compilation cycles and reducing development costs while giving you instant access to leverage the whole wealth of Java libraries out there.

What is Helma?

Started in 1997
- orf.at Montagesystem
- Weblogs, "classic" helma
Conceptual roots: Java, Object oriented databases, ASP
Community: Small, pretty loyal, slightly disfunctional
Users: orf.at, twoday, antville, many "small" sites and developers
helma.org

Why Helma?

The top 10 reasons to give it a shot

Helma is JavaScript! Well known, well established scripting language. Same language as on client-side
Helma is Java! Scripted applications are compiled to Java, and server-side Java has proven to be quite fast and reliable
Use existing Java-Libraries! Any available Java-library can be made accessible for the scripting environment. see here
A light-weight. Rather small memory footprint, and is fast on start-up.
Helma is open-source! BSD-style license

Why Helma?

The top 10 reasons to give it a shot

Transparent database-mapping
Efficient caching mechanism
Smart (yet quite restrictive) templating mechanism
Session management
Integrated scheduling mechanism

What is Helma really?

Helma is a highly integrated Web stack consisting of:

Rhino, a Mozilla project, JavaScript implemented in Java
Jetty, a full-featured, embeddable web server/servlet engine
A web scripting framework combining the above plus a number of other Java libraries
A homegrown object-relational database mapping layer
Increasingly, a number of JavaScript libraries to enhance the language and support common tasks

Hands On Session

Hello world!
Javascript
Prototyping
DB Mapping
Object Modelling
Rendering Framework
Java - JCaptcha

download helma-1.5.3 plus source code of this demo session

Hello world michi/192.168.0.108!

Download and install Helma

> wget http://adele.helma.org/download/helma/1.5.3/helma-1.5.3.tar.gz
> tar -xvzf helma-1.5.3.tar.gz
> cd helma-1.5.3
> ./start.sh

Write the application

> echo 'helloworld' >> apps.properties
> mkdir -p apps/helloworld/Root
> nano apps/helloworld/Root/functions.js
  function main_action() {
    res.write("Hello " + java.net.InetAddress.getLocalHost());
  }

-> http://localhost:8080/helloworld

Javascript

var str = "This is a String."; // This a comment 
str += " And another one appendend."; 
str = str.substring(str.indexOf("."), str.length - 3); 

var arr = new Array();
arr[0] = "value01"; 
arr.push([1,2,3,4]);
arr.push({name: "product", price: 12.3});

var j = 0; 
for (var k=0; k<10; k++) { 
   if (k%2 == 0) continue; 
   j += k; 
} 

function obj() {
  // ...
}
obj.prototype.someMethod = function() {
  // ...
}

try { 
   someUndefinedFunction(); 
} catch (err) { 
   return "Error occurred!"; 
}

http://www.slash7.com/articles/2006/07/26/javascript-boot-camp-tutorial

Host Objects

Request req
Response res
Session session
Application app
Root root

if (req.data.register) {
  root.registerUser(req.data);
  res.redirect(root.href());
}
res.write("Hello " + (session.user ? session.user.name : "anonymous"));

Prototyping

We define a Prototype 'Person' and instantiate, persist, modify and remove it. See the HopObject-reference.

  
=== [HelmaDir]/apps/demo/Root/functions.js === 
 
function main_action() { 
   // list all Persons 
   for (var i=0; i<root.count(); i++) { 
      var p = root.get(i); 
      res.write("<li>");
      res.write(p.name + " "); 
      if (p.dateofBirth) res.write(p.dateOfBirth.format("dd.MM.yyyy") + " "); 
      res.write("<a href=" + p.href("edit") + ">edit this Person</a>"); 
   } 
   // render link to create a new person
   res.write("<br /><a href=" + this.href("createPerson") + ">create new Person</a>");
} 
 
function createPerson_action() { 
   if (req.isPost()) { 
      // instantiate a new object of type 'Person' 
      var p = new Person(); 
      // set the property 'name' of the new Person 
      p.name = req.data.name; 
      // set a integer value 
      p.bodySize = 180; 
      // set the date of birth 
      p.dateOfBirth = new Date(1978, 4, 24); 
      // store the new object persistently 
      root.add(p); 
      // now redirect the client to the list of all Persons 
      res.redirect(this.href("main")); 
   } 
   this.renderSkin("createPerson"); 
} 
 
=== [HelmaDir]/apps/demo/Root/createPerson.skin === 
 
<form action="" method="POST"> 
  <input type="text" name="name"> 
  <input type="submit" name="send" value="create new Person"> 
</form> 
 
=== [HelmaDir]/apps/demo/Person/functions.js === 
 
function edit_action() { 
   // if the form has been submitted... 
   if (req.isPost()) { 
      // ... change the name of that person 
      this.name = req.data.name; 
      // ... and redirect to the root main action 
      res.redirect(root.href("main")); 
   } 
   this.renderSkin("edit"); 
} 
 
function constructor() {
   // a constructor can be optionally defined for each
   // prototype in order to have programm code being
   // executed whenever a new Object is instantiated
   ;
} 
 
 === [HelmaDir]/apps/demo/Person/edit.skin ===
 
<form action="" method="POST"> 
  <input type="text" name="name"> 
  <input type="submit" name="send" value="change name"> 
</form>

Please, ignore the fact for a while that we clearly violated MVC-principles in the above code. The goal of this mini-app is to demonstrate the HopObject-methods.

DB Mapping

We will map the defined prototype on a database. See the Mapping-reference.

You will need to have MySQL installed, execute mysql.sql on your database, put the jdbc-driver from mysql.com into [HelmaDir]/lib/ext, delete [HelmaDir]/db/demo and restart Helma.


=== [HelmaDir]/apps/demo/db.properties ===

jad.url      = jdbc:mysql://localhost/demo 
jad.driver   = com.mysql.jdbc.Driver
jad.user     = helma 
jad.password = secret

=== [HelmaDir]/apps/demo/mysql.sql ===

CREATE DATABASE demo; 
USE demo; 
 
GRANT ALL ON demo.* TO helma@localhost IDENTIFIED BY 'secret'; 
 
CREATE TABLE person ( 
  person_id MEDIUMINT(10) NOT NULL, 
  person_name TINYTEXT, 
  person_height TINYINT unsigned, 
  person_dateofbirth DATETIME, 
  PRIMARY KEY (person_id) 
);

=== [HelmaDir]/apps/demo/Root/type.properties ===

_children = collection(Person)

=== [HelmaDir]/apps/demo/Person/type.properties ===

_db = jad 
_table = person 
_id = person_id 

name = person_name
height = person_height
dateOfBirth = person_dateofbirth

=== [HelmaDir]/server.properties ===

logDir = console

=== [HelmaDir]/apps/demo/app.properties ===

logSql = true

=== [HelmaDir]/lib/ext/mysql-connector-java-5.0.3-bin.jar ===

HopObject Caching

Long-running, multithreading single process is ideal for simple in-process caching
Caching via Least Recently Used (LRU) Hashtable, implemented using two rotatating Hashtables internally
Each object exists exactly once at each time
Concurrency considerations are really important

HopObject Collection Caching

HopObject collections are ordered (lists)
Any change in any object may affect collection membership or order
Conservative default behavior: better to reload than to be wrong
Options for more aggressive caching

Object Modelling

We will define a prototype 'Organisation'. Each person may belong to a Organisation.

=== [HelmaDir]/apps/demo/mysql.sql === CREATE DATABASE demo; USE demo; GRANT ALL ON demo.* TO helma@localhost IDENTIFIED BY 'secret'; CREATE TABLE person ( person_id MEDIUMINT(10) NOT NULL, person_name TINYTEXT, person_height TINYINT unsigned, person_dateofbirth DATETIME, person_org_id MEDIUMINT(10) unsigned, PRIMARY KEY (person_id) ); CREATE TABLE organisation ( org_id MEDIUMINT(10) unsigned NOT NULL, org_name TINYTEXT, org_country TINYTEXT, PRIMARY KEY (org_id) ); CREATE INDEX idx_pers_org ON person (person_org_id); INSERT INTO organisation values (1, "knallgrau", "at"); INSERT INTO organisation values (2, "helma", "at"); INSERT INTO organisation values (3, "amazon", "us"); INSERT INTO organisation values (4, "ebay", "us"); INSERT INTO organisation values (5, "yahoo", "us"); INSERT INTO person values (1, "michi", 180, "1978-05-24", 1); INSERT INTO person values (2, "matthias", 179, "1976-06-22", 1); INSERT INTO person values (3, "dieter", 176, "1978-06-13", 1); INSERT INTO person values (4, "hannes", null, null, 2); INSERT INTO person values (5, "weirdo", 185, null, null); === [HelmaDir]/apps/demo/Root/type.properties === organisations = collection(Organisation) organisations.accessname = org_name allPeople = collection(Person) tallPeople = collection(Person) tallPeople.order = person_height DESC tallPeople.filter = person_height >= 180 === [HelmaDir]/apps/demo/Organisation/type.properties === _db = jad _table = organisation _id = org_id _parent = root.organisations persons = collection(Person) persons.local = org_id persons.foreign = person_org_id persons.accessname = person_name persons.order = person_name name = org_name country = org_country === [HelmaDir]/apps/demo/Person/type.properties === _db = jad _table = person _id = person_id _parent = organisation.persons, root.allPeople name = person_name height = person_height dateOfBirth = person_dateofbirth organisation = object(Organisation) organisation.local = person_org_id organisation.foreign = org_id === [HelmaDir]/apps/demo/Root/functions.js === function main_action() { // list all Organisation and their Persons for (var i=0; i<root.organisations.count(); i++) { var org = root.organisations.get(i); res.write("<h3>" + org.name + " (" + org.country + ")</h3>"); for (var j=0; j<org.persons.count(); j++) { var p = org.persons.get(j); res.write("<li>"); res.write(p.name + " " + (j+1) + " of " + p.organisation.persons.count()); res.write(" <a href=" + p.href("info") + ">info</a>"); } } res.write("<br /><a href=" + root.href("tallPeople") + ">tall People</a>"); } function tallPeople_action() { for (var i=0; i<root.tallPeople.count(); i++) { var p = root.tallPeople.get(i); res.write("<li>" + p.name + " " + p.height + "</li>"); } } === [HelmaDir]/apps/demo/HopObject/functions.js === function info_action() { res.write("HELLO " + this._prototype.toUpperCase() + " " + this._id); }

Object Model directly affects request path structure.
Can be overridden by implementing getChildElement(), but it rarely is.

Rendering Framwork

Actions, Skins, Macros => MVC.
See http://helma.org/docs/guide/framework/.

=== Root/functions.js === function main_action() { res.data.body = this.renderSkinAsString("main"); renderSkin("html"); } === Global/html.skin === <html> <body> <h1>The demo app</h1> <div><% response.body %></div> </body> </html> === Root/main.skin === <h2>Organisations</h2> <% this.list collection="organisations" skin="listItem" prefix="<ul>" suffix="</ul>" %> === Organisation/listItem.skin === <h3><% this.name %></h3> <ul><% this.list collection="persons" skin="listItem" %></ul> === Person/listItem.skin === <li> <% this.name %> <% this.dateOfBirth prefix=" (" suffix=")" %> <a href="<% this.href action="edit" %>">edit</a> <% organisation.name %> </li> === Person/macros.js === function dateOfBirth_macro(param) { if (!this.dateOfBirth) return; res.write(this.dateOfBirth.format(param.format || "dd.MM.yyyy")); } === HopObject/macros.js === function href_macro(param) { res.write(this.href(param.action || "")); } function list_macro(param) { var coll = param.collection ? this[param.collection] : this; for (var i=0; i<coll.count(); i++) { coll.get(i).renderSkin(param.skin); } }

Note: Hannes on history of rendering framework, current development and alternatives such as velocity.

Rendering Framework past, present and future

Past: HSP (Helma Server Pages). Templates mixed with JS code, executed as functions
Present: Skins and Macros. Rigid separation of form (skins) and content (macros). Macros are special functions provided by application objects.
Future: Helma template engine implemented in JavaScript instead of Java; Alternative Velocity and Freemarker template engines by Jürg Lehni.

Java Integration - JCaptcha

JCaptcha: Java-Library for generating Captcha-Images.


=== Root/functions.js ===

function modJCaptcha_jpg_action() {
   if (!app.data.modJCaptchaService) {
      app.data.modJCaptchaService = new Packages.com.octo.captcha.engine.image.gimpy.DefaultGimpyEngine();
   }
   session.data.modJCaptcha = app.data.modJCaptchaService.getNextCaptcha();
   var challenge = session.data.modJCaptcha.getImageChallenge();
   var jpegOutputStream = new java.io.ByteArrayOutputStream();
   var jpegEncoder = Packages.com.sun.image.codec.jpeg.JPEGCodec.createJPEGEncoder(jpegOutputStream);
   jpegEncoder.encode(challenge);
   res.contentType = "image/jpeg";
   res.writeBinary(jpegOutputStream.toByteArray());
}

function main_action() {
   if (req.data.word) {
      if (session.data.modJCaptcha.validateResponse(req.data.word))
         res.write("<b>OK</b><br />");
      else
         res.write("<b>NOK</b><br />");   
   }
   res.write("<img src=\"" + this.href("modJCaptcha.jpg") + "\">");
   res.write("<form action=\"\"><input name=word><input type=submit></form>");
}

Where is Helma going?

Helma 2 is a fresh implementation of Helma.

Keep the good things, cut the cruft
Many things have changed in Java libraries (both core and 3rd party)
We have learned a thing or two
Don't reinvent the wheel (even if we were actually first)
Don't put things in Helma core that you can script

Helma (re-)organization

Install some simple, common rules (aka bylaws)
Distribute development and share responsibilities
Try to attract more good people

Helma @ Metalab • 7.11.2006

Welcome to Helma!

Welcome to Helma!

Hannes Wallnöfer

Michael Platzer

What is Helma?

Helma is a scriptable, open-sourceJava Web Application Server

What is Helma?

Why Helma?

The top 10 reasons to give it a shot

Why Helma?

The top 10 reasons to give it a shot

What is Helma really?

Hands On Session

Hello world michi/192.168.0.108!

Javascript

Host Objects

Prototyping

DB Mapping

HopObject Caching

HopObject Collection Caching

Object Modelling

Rendering Framwork

Rendering Framework past, present and future

Java Integration - JCaptcha

Where is Helma going?

Helma (re-)organization

Helma is a scriptable, open-source
Java Web Application Server