Wednesday, January 22, 2003

Using context params or JNDI for configuration

Jasper is configured using servlet init params, specified in web.xml. You can

customize per context - by defining a jsp servlet using a special name.

The problem: that would make your app unportable, it won't work with other jsp engines.

An alternative would be to use context params and init params of the

compiled servlet - with some special names that would be used by jasper.

Jasper would read global options from the context init params, then override

with local init params defined in the servlet (with jsp-page) tag. Options

names can be generic "jsp.keepgenerated" or "jasper.keepgenerated".

As API, we should _stop_ the use of Options interface ( and add a method for

every option we add ) and start using a simple getInitParam( String ). Or even better -

use JMX to push config options into the JSP engine ( which can be jasper or something else ).

There are many benefits:

* simpler configuration

* relatively portable - other engines can just ignore jasper settings. Right now

if you make per-context settings - the app won't work with other engines

* other engines may support same options

* it works very well for runtime options ( like what kind of thread pool to use )

* it works very well for precompiled JSPs ( which bypass JspServlet )

* general config tools can be used ( anything that supports web.xml config ), you

don't need jasper-specific GUI

* very easy and flexible

Another (probably) alternative is to use JNDI env entries. This is more powerfull -

as it allows the most flexibility in configuration, and is also supported

in the standard web.xml.

Possible naming conventions:

* java:env/PREFIX/SERVLET_NAME/JSP_OPTION - per page option, affects only a specific page

* java:env/PREFIX/global/JSP_OPTION - per context option, affects all pages ( unless overriden)

* /PREFIX2/jsp/JSP_OPTION - per server ( defined in server.xml ).

Another option - more powerfull if preffer a single config store ( LDAP, JDK1.4 prefs, etc ):

* /PREFIX1/INSTANCEID/VHOST/WEBAPP/PREFIX2/SERVLET_NAME/OPTIONS -> that will configure a specific instance

* global settings by using "Default" for different components.

PREFIX will avoid conflicts with other jndi entries. ( "options" ? )

Same mechanism can be used for the DefaultServlet, and also to set per context attributes

that are typically set in server.xml.

Future versions of the servlet spec - or de-facto standards - may define some cross-container

options ( jsp_keep_generated seems like a good one ).

The container should have control on allowing some options to be specified by individual apps -

probably the policy would do it ( it's already available if JNDI is used ).

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