EQUIP2 WebApp Scripting Support

Chris Greenhalgh, 2007-02-06

Introduction

For some applications and for intial development prototyping it may be preferred by some developers to use a scripting language to develop controllers (which may then be ported to native Java controllers).

The tutorial has examples of using the Apache Jakarta Bean Scripting Framework (now becoming a JCP standard) to create controllers whose main functionality is specified by a script.

Note that scripting support may become a more core feature of EQUIP2 at some point, and/or the (reusable) sample scripting controllers may be migrated to the equip2webapp library.

First example

The servlet 'scripting', configured by WEB-INF/scripting-servlet.xml, has one configured page which uses a scripting-based controller: the URL http://.../scripting/first_script.html is mapped to an instance of the reusable scripting controller class equip2.webapptutorial.scripting.ScriptingAbstractController. This is configured in scripting-servlet.xml as follows:

	<bean id="firstScriptController"
		class="equip2.webapptutorial.scripting.ScriptingAbstractController">
		<property name="scriptResource" value="equip2/webapptutorial/scripting/first_script.py" />
		<property name="dataspace"><ref bean="dataspace"/></property>
	</bean>

The property 'scriptResource' is a Java resource path to the script file which is called to implement the standard abstract controller method:

protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response)
    throws Exception;

In the tutorial example, the build process copies script file(s) from the src/ directory hierarchy into the build and hence to the web applications classes/ directory hierarchy. In this case, the script file is src/equip2/webapptutorial/scripting/first_script.py:

# this is the body of a function with signature (thisref, request, response)
# it handles a standard spring request, and should return a ModelAndView

# ModelAndView
from org.springframework.web.servlet import ModelAndView
mav = ModelAndView()
mav.viewName = 'scripting/first_script_success'
model = mav.model
model.put('answer',42)

# example of accessing dataspace
session = thisref.getDataspace().getSession()
session.begin()
from equip2.core import QueryTemplate
from equip2.webapptutorial.db import Player
from java.lang import Class
query = QueryTemplate(Class.forName('equip2.webapptutorial.db.Player'))
players = session.match(query)
session.end()

model.put('players', players)

return mav

The script is run using BSFs apply method, which converts it into the body of an unnamed function and calls it with specified arguments [actually this is currently broken for Jython, so we work around it ourselves], but it generally looks the same. This example shows both creating a ModelAndView for rendering, and accessing the application dataspace (via the property 'dataspace' defined in the scripting controller class).

The final view, as expected, is rendered by the JSP scripting/first_script_success.jsp

Note that the script execution currently re-reads the script file every time it is called, so:

there is a performance overhead
the script can be updated just by copying in a new version (or editing in place)

Reusable Controllers

The following reusable scripting controller currently exist, and can be used in place of the corresponding Spring base class to have a scripting main handling method (configured, as above, via the scriptResource property):

equip2.webapptutorial.scripting.ScriptingAbstractController, which extends org.springframework.web.servlet.mvc.AbstractController, and calls the configured script to handle
protected ModelAndView handleRequestInternal(HttpServletRequest request, HttpServletResponse response) throws Exception
equip2.webapptutorial.scripting.ScriptingAbstractCommandController, which extends org.springframework.web.servlet.mvc.AbstractCommandController and calls the script to handle
protected ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws Exception
equip2.webapptutorial.scripting.ScriptingSimpleFormController, which extends org.springframework.web.servlet.mvc.SimpleFormController and calls the script to handle
protected ModelAndView onSubmit(HttpServletRequest request, HttpServletResponse response, Object command, BindException errors) throws Exception

Common script support is provided by equip2.webapptutorial.scripting.ScriptManager. The Script Manager method(s) callScript/callScriptLiteral could also be used to introduce scripting into other point in an application.

Refer to the BSF documentation for details on how to add support for other scripting languages (the main thing should be to copy the relevant JARs into the Web application on deployment).

Changes

2007-02-06

document created