Serve clients' specific protocol requirements with Brazil, Part 5

Manage users and content with Brazil

By Rinaldo Di Giorgio, JavaWorld.com, 08/24/01

Read the whole series on Brazil technology:

• Part 1: Learn how to build an application server that can deliver data to clients requiring different protocols
• Part 2: How to support XML applications with the Brazil project
• Part 3: Economically sustain PQA, UP.SDK, and J2ME with the Brazil project
• Part 4: Build multicast-aware apps with JRMS
• Part 5: Manage users and content with Brazil
• Part 6: Plug Jini, BeanShell, and JAXM into Brazil

To show how Brazil can create new content from existing content, I will demonstrate how it allows users to create their own portfolios, remembers this information, and delivers the data as a Web service. In addition, in this article I'll show you how to parse non-XML-based content. Many Websites don't provide XML representations of their data, and while that isn't always a showstopper, some Websites produce content in such a way that the data is nearly impossible to parse. Using Brazil, you can process this content to create new XML-enabled data.

I begin by discussing how to configure the Brazil technology using a config file. I then go over our sample application's two main files: index.html and GetNews.html. The file index.html is used at http://www.digiorgio.com:9001/ by default, while the file GetNews.html is called periodically to parse the news information. (The support Website www.digiorgio.com runs several Brazil servers and hosts the Web application I discuss in this article at port 9001.) These two files and the config file are all you need to implement a system that supports many user accounts featuring dynamic news and stock price data.

Readers interested in creating their own Websites can download the following software packages from Resources:

• The Brazil distribution
• The Jython distribution
• config
• index.html
• GetNews.html

Once your application is up and running, please email me.

Configure the Brazil server

In this article, we will work with several handlers and templates to develop a Website that provides session tracking, allows users to customize the Website, integrates contents from diverse Websites, and utilizes Brazil Scripting Language (BSL) and Jython to manipulate content easily. Jython is a 100 percent pure Java implementation of Python. As an interpreted language, Python facilitates program writing and testing. Python programs are compact and readable, and the language includes a rich set of libraries. Jython, which is Python supporting a Java interface, is an excellent replacement for Perl and Tcl. Jython allows you to run Python on any Java platform. See Resources for more information.

When you start Brazil, you need to specify a config file or a series of config files, like so:

java -Dpython.home=. sunlabs.brazil.server.Main -config config

These config files are nothing more than Java properties files, which use the format name=value to determine the various handlers' configuration. Java applications can easily manipulate properties files. See the Java documentation for java.util.Properties.

You must understand these files in order to configure the Brazil server. The config file below comes from the server running at http://www.digiorgio.com:9001.

You define values for properties that all handlers, filters, and templates access by setting a name to a value. The code below sets the log level, the port that listens for requests, control over printing properties, and whether or not to exit when the server reports an error:

log=5
port=9001
root=doc
debugProperties=on
exitOnError=true

Our example will support the stocks listed below. We must limit them since our free service is for instructional use only. Stability issues for reporting the prices of 10,000 different stocks have been considered but not tested in a running system:

stocklist=SUNW LU CIEN NT GLW JDSU AVNX A BRCM TERN  CNXT LOR GSTRF 
QCOM  PCS MOT LVLT MFNX GBLX NOPT WCOM NOVL XLA PRCM STOR ADI AMCC ATML 
CUBED LSI NSM TXN XLNX

Brazil uses a special token called a handler to determine which handler list to start with. In this case, we tell the Brazil server to look for a property with the prefix main:

Note: In Python/Jython code, the # character indicates a comment.

handler=main
#--------------------------------------------------------------------
----
# Here's where it all starts
main.class=sunlabs.brazil.server.ChainHandler
main.handlers=pollnews pollstock session persist savestate filter 

The prefix.class identifies the Java classfile to run for the specific handler. The selected handler sunlabs.brazil.server.ChainHandler understands additional properties; for instance, it understands main.handlers, which has a list of additional handlers, templates, and filters to run. The chain handlers call each handler in the list for each input request. The first called handler is pollnews, with several additional properties specified with the same prefix. The configuration properties below instruct the Brazil server to periodically call the Python script in the file GetNews.py. The file GetNews.py is a Jython script that reformats data from other Websites and makes this data available to other handlers, templates, and filters:

#--------------------------------------------------------------------
----
# Fetch the news
pollnews.class=sunlabs.brazil.handler.PollHandler
# how often to fetch new news every 5 minutes
pollnews.interval=300
# do a fetch at startup, before waiting for "interval"
pollnews.fast=1
# prefix all results with this string
pollnews.prepend=
# set the .py suffix as a recognized mime type
mime.py=text/python
# the url from which to get the news
pollnews.url=http://localhost:9001/GetNews.py

The next handler in the chain, pollstock, uses the same pollhandler to periodically request stock price information instead of stock news information. The stock data returns in name=value pairs with stock. added to each value so we receive different values like this: stock.SUNW.price=17.5:

#--------------------------------------------------------------------
----
# Fetch stock quotes from yahoo
# url:
#    
http://quote.yahoo.com:80/d/quotes.csv?s=sunw+msft&f=sl1d1t1&e=.csv
# result:
#   "SUNW",19.75,"5/4/2001","1:19PM"
#   "MSFT",70.10,"5/4/2001","1:19PM"
pollstock.class=sunlabs.brazil.handler.RePollHandler
# how often to fetch new quotes
pollstock.interval=30
# do a fetch at startup, before waiting for "interval"
pollstock.fast=1
# prefix all results with this string
pollstock.prepend=stock.
# You can send a request here to change the url on the fly, 
# thus dynamically modifying the list of stocks to retrieve
pollstock.prefix=/pollstock
# uncomment and fill in to use your favorite proxy, if you need 
one
# pollstock.proxy=
# the token denoting the regular expression that will be applied to 
content
pollstock.re=pollextract
# The url to get the stock quotes (the symbols are hard-wired for 
now)
pollstock.url=http://quote.yahoo.com:80/d/quotes.csv?f=sl1d1t1c&e=.cs
v&s=SUNW+LU+CIEN+NT+GLW+JDSU+AVNX+A+BRCM+TERN+CNXT+LOR+GSTRF+QCOM++PCS+MOT+
LVLT+MFNX+GBLX+NOPT+WCOM+NOVL+XLA+PRCM+STOR+ADI+AMCC+ATML+CUBED+LSI+NSM+TXN
+XLNX
#--------------------------------------------------------------------
----
# This is the regular expression that turns the csv format file from 
yahoo
# into a name/value "properties" list
pollextract.exp="([^"]*)",([^,]*),"([^"]*)","([^"]*)","([^ ]*) - 
([^"]*)"
pollextract.sub=\\1.price=\\2\n\\1.date=\\3\n\\1.time=\\4\n\\1.change
=\\5\n

The Brazil server supports session tacking with or without cookies. If a user turns cookies off, the session filter provides an ID that can be appended to the URL to provide URL tracking information. Before cookies became popular, early Web servers tracked users with this same technique:

#--------------------------------------------------------------------
----
# Do session tracking. Use browser cookies where
# possible, and URL rewriting otherwise.  This
# filter gets called as a handler first (even
# before the content is generated), to extract the
# session information, then again as the last
# filter to (if needed) add the session information
# back onto the urls.
session.class=sunlabs.brazil.filter.SessionFilter
# the name of the cookie is passed to the browser
session.cookie=JavaWorld-Brazil
# causes cookies to be set so they persist across browser 
"instances"
session.persist=true

When a user loads the index.html page, the SessionFilter looks for any session information. If this information exists, it loads into the user's session object. As the user interacts with the system, session data is modified and created; this data must be saved. In our example, the data is not stored in a database. In order to maintain sessions, the session information should back up to disk in case the server fails and needs restarting. Commercial implementations would use a properties cache manager that maintains the ACID properties using a database or fault-tolerant memory.

The ACID properties are:

• Atomic -- transactions happen indivisibly
• Consistent -- there are no violation of system invariants
• Isolated -- there are no interference between concurrent transactions
• Durable -- after transaction commits, changes are permanent (persistent)

The code below demonstrates how to save our data: