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javajspjakarta-eeapplication-server

Interact with JSP compiler

I have some text templates stored in a database. We need to use a templating engine to process these texts. We first thought of Velocity / Freemaker / Thymeleaf to process these texts. However, I thought (but could be wrong) that one could interact with the application server JSP compiler. I'd prefer to use JSP compiler rather than importing a new bunch of jars.

Thanks

Solution

  • AFAIK they are different concepts and work differently so they won't directly interact :

    • JSP is processed by a JSP compiler to generate java code for a servlet that is compiled (at run-time) in a .class file. It is later used by the servlet container as any other servlet. You can include any java code in a JSP with scriptlets (even if it now considered as bad practice)

    • template engines (Velocity / Freemaker / Thymeleaf) take a template and only allow to replace variable place holders with values at run time to produce text. Of course, they also allow tests and loops, but no java source nor class object is ever generated. In a web application they use one single servlet that takes the template and the replacement values and generate the text that will be sent in the response.

    But of course as JSP can contain arbitrary java code, you could call a template engine from a JSP, but I really cannot imagine a proper use case.

    Edit per comment:

    You could try to use JSP as a template engine, but my advice is : don't do that ! You would need :

    • create a stub implementing ServletResponse where the getOutputStream() and the getWriter() methods end in a String.
    • force the ServletContainer to generate the java source and the class file - or manage to do that at compile time (I don't know how exactly how to do that, but I'm pretty sure it can be done)
    • at run time include the generated servlet with the response stub to generate the output String.

    But beware, even if you succeed, it will lead to hardly maintainable code heavily coupled to a servlet container or using special steps (JSP -> java) at build time. As already said : don't do that.

    I've just come to JSP compilation to string or in memory bytearray with Tomcat/Websphere, looks like your question is a duplicate of that one ...