Ideas for the migration, if migration is on your mind.
Inside or outside the database,
* squeeze as much business rules into DB as possible. Unique constraints, referential integrity (triggers), check constraints, input validation constraints for insert/update/delete, not-null constraints, stored proc, triggers, user-defined functions …
* Without an enormous effort, you can move every single SQL out of java/php/asp source and into some (xml) “query-listing” file. Every SQL sent to the DB will be taken from this listing. Performance penalty can be managed with some kind of simple caching, which I think can be quite effective.
* Many if not most jsp projects encourage a DAO pattern, sometimes quite elaborate or sophisticated. PHP supports DAO patten in PEAR::DB, albeit lightly. It helps your migration. However, small PHP sites may not warrant the extra effort
* Avoid Object-Relational-Mapping tools such as Hibernate or iBatis, since PHP isn’t comfortable with ORM yet.
With regard to so-called “presentation layer” or page templates
* smarty and JSP-EL/JSTL are highly recommended. They are simple and straight-forward. With them you can create templates free of business logic. The only “programming” remnants left in the template are simple variables, and the simplest loops and if-then-else — all easy stuff to migrate between jsp and php.
* Not sure if AJAX is necessary for your site. AJAX requires you to create special server-side components. The browser-side ajax function communicates with the server-side components. Server-side components are coded in php or java or asp.
Lastly, we finally turn our attention to the jsp/php files. Even with the DB/presentation layer hacks, some, perhaps the bulk, of the functionality may remain in your java/php source code. You need to think of server-side software design ideas that are transferrable between jsp/php/asp. Many things to consider. Here are A few trivial items.
* avoid servlet/jsp forward. I don’t think php supports it.
* PHP guys tend to put a few related functionalities into one php file, motivated by maintainability, readability and other reasons, whereas jsp/servlet tends to separate them into individual jsp files (even separate javabean/servlet classes). The java approach is viable in PHP too, and helps migration.
* If you need automated testing, consider black-box test tools. These are transferrable and agnostic to the server-side language, be it jsp or asp or whatever