When enabled, the pre-touch mechanism causes all JavaServer Pages files to be compiled within the Web module for which they are configured. You can also configure some or all JSP files to be class loaded and JIT-compiled. To enable the pre-touch mechanism, use the Application Server Toolkit (AST) to specify the following JSP attributes, which are Assembly Property Extensions for your Web module:
Note: JSP ile compilation is different from JIT compilation. JSP compilation generates bytecodes, whereas JIT translates the bytecodes into machine code at run time.
The pre-touch mechanism compiles and JIT-compiles JSP files by directly invoking the JSP service method, thus making the JSP file susceptible to incurring exceptions because it is called out of context. Such exceptions are avoided by immediately checking the value of this attribute, causing a quick exit from the service method when the JSP was prepared by this tool. This attribute value is added as a request parameter and is composed of alphanumeric characters that your JSP files do not expect to use during normal execution.
Set this numeric attribute to the number of threads that you would like this mechanism to start up to compile your JSP files. Since a thread makes use of just one processor, multi-processor systems may better utilize this pre-touch mechanism by specifying a value greater than 1. The default setting for this attribute is 1, representing the number of threads that are created to perform pre-touch processing for this Web module.
Set this attribute to either a whole number or the word changed. By entering changed, only those JSP filess that have been updated or not previously touched, for example, those JSPs that need to be converted from a .jsp file to a .java file, are class loaded. By entering a numerical value, for example, 1000, the pre-touch tool starts class loading at the 1000th JSP that it processes and all subsequent JSP files. This is convenient in the event that the application server is stopped when starting the pre-touch tool. You can then check the server logs to see how many JSP files have been processed and update the prepareJSPClassload value accordingly to avoid duplicating work. If a JSP file is not class loaded, it cannot be JIT compiled. As a result, if a JSP does not satisfy the requirements of the prepareJSPClassload attribute, but satisfies the requirements of the prepareJSPs attribute, the JSP file is compiled if it has been updated, but is not class loaded or JIT compiled.