Category Image Simple Java Server 


A brief intro to the Simple Java Server. 

In September 2004, I was contracted to write a Java-based server architecture for creating inetd-like daemons in an object oriented manner, which could be dynamically plugged and unplugged, with a full administrative interface using RMI.

The project was a success development wise, but after the customer signed off on the project, they disappeared without payment (the full, sordid details in in two SlashDot journal entries here and here). Out $1000 (CDN), I decided to cut my losses, learn a lesson about taking on a project from another country without receiving an up-front payment, and decided to Open Source everything.

SJS is a very powerful architecture which is especially suited to creating servers which use a request/response style service, such as those used in POP3 and SMTP (indeed, originally I was supposed to be contracted to write plug-ins for the server for each of these protocols, but that fell through once the jokers who contracted me buggered off and stopped responding to my messages). And you don't even need to know anything about networking to use it -- just create a subclass of the AbstractRequestResponseAdapter class and implement a single method -- processRequest() which takes as input a single String (the request), and which returns a single String (the response). With that built, create an XML file describing what port to listen against, the maximum number of simultaneous requests to handle (if desired), a service name, and presto -- you have a complete server that does what you want.

There is also an AbstractAdapter class which you can use to create services which aren't request-response based if you want to do something more complex, but you're going to need to know a bit about Java network programming to use it.

SJS's administrative interface uses RMI to connect to the server and modify any of its services in real time. The command set for the administrative tool includes:

CREATE <ip address>:<port> name="<service name>" adapter="<full path>"
SET [<ip address>:<port> | name="<service name>"] <parameter name>="<parameter value>"
DESCRIBE [<ip address>:<port> | name="<service name>"]
DESCRIBE [<ip address>:<port> | name="<service name>"] <parameter name>
REMOVE [<ip address>:<port> | name="<service name>"]
REMOVE [<ip address>:<port> | name="<service name>"] <parameter name>
DENY INCOMING REQUESTS [<ip address>:<port> | name="<service name>"]
ACCEPT INCOMING REQUESTS [<ip address>:<port> | name="<service name>"]
STATUS [<ip address>:<port> | name="name"]
START SERVER [server config file]
SHUTDOWN [NOW]

Many of these commands will also modify the XML data files to reflect your changes -- so if you change the listen-to port for a service, it not only changes immediately, but the change will be saved in the XML configuration file for the service as well.

I'm extremely proud of this piece of work, as it makes creating a server in Java a complete snap which even a neophyte network programmer can use to create robust server applications. Unfortunately it's little known, and so far as I know isn't used anywhere. If you're looking to write your own server software in Java, especially if it's request-response style, take a look at what SJS can do for you (but note that SJS is 100% GPL -- if the company which screwed me wants to sell solutions based on this code as they originally intended, they have to give their customers all the source as this is the only license SJS is available under). 

Posted: Saturday - April 02, 2005 at 01:41 AM          

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