The Design Time Application Manager
|
Overview
The Design Time Application Manager (DTAppMgr), defines the early stages
of a mechanism to simulate JSF runtime state conditions at design
time. While it is not intended to replace a runtime simulator, it
provides an extensible framework to allow adopters to provide end-user
features that depend on simulating certain specific runtime
behavior. These features include validation and content assist for
EL expressions.
The DTAppMgr is comprised of the following main components:
- a simulated FacesContext, called DTFacesContext, used to
simulates part of this key runtime context object.
- a pluggable ExternalContext, called DTExternalContext to
support different behaviors in different containers (i.e. JSP).
- pluggable resolvers for EL variables, properties and methods
including default implementations.
- a JSP processor that can update simulated design time state
based on a JSP page and tag-based meta-data.
The simulated
FacesContext
The simulated FacesContext, called DTFacesContext, currently supports a
very limited subset of the runtime FacesContext object. Its main
function is to allow for a pluggable external context. At
design-time, one FacesContext is created per IFile.
Pluggable ExternalContext
The ExternalContext is used to separate container-dependent context
information from the rest of the FacesContext. At design time, we
support a DTExternalContext with much the same function. This
external context can be configured by adopters by implementing a factory
extension point. The extension point is
org.eclipse.jst.jsf.designtime.externalcontext. You extension will
define an id and class. The id uniquely identifies you factory
class, which must extend
org.eclipse.jst.jsf.designtime.context.AbstractDTExternalContextFactory
. To set your external context factory as the current one, use
DesignTimeApplicationManager.setExternalContextProvider(String)
. Note that by changing the current ExternalContextProvider on a
project, you will significantly change the behavior of how variables are
resolved in EL expressions.
Pluggable resolvers
JSF EL expressions may contain variable and method bindings that
reference external objects. At runtime, this is accomplished
through several mechanisms that convert different types of identifier
symbols into objects and methods. At design-time the JSF tooling
tries to parallel these as closely as possible. These mechanisms
are:
- VariableResolver
- PropertyResolver
- MethodBinding
VariableResolver
All identifier symbol resolution in EL starts with the
VariableResolver. An expression like "myBean.property" is resolved
by first extracting the symbol "myBean" and requesting the
VariableResolver to return a matching runtime object. At design
time, we parallel this exactly but constructing a design-time
description of the object rather than its actual value (since the actual
value cannot be fully computed until runtime in most cases). The
concept of a "DTVariableResolver" is introduced. A default
implementation is automatically provided which closely mirrors the
default runtime resolver. New variable resolvers can be
contributed through the Eclipse extension point mechanism to support
custom runtime counterparts. To learn more about contributing new
variables, see
ContributingEL Variables.
PropertyResolver
Once a variable is resolved, the next step in resolving a value
binding is to resolve its properties. To return to our simple
example, "myBean.property", the JSF runtime will pass the object
returned for 'myBean' to the property resolver along with the name
'property' and ask it to resolve it to an object. At design time,
we parallel this by introducing the "DTPropertyResolver".
MethodBinding
The method binding mechanism implemented by the JSF runtime,
differs from the way variables and properties are resolved. At
design time however, we support them in the same way by providing a
"DTMethodResolver". The main reason for this divergence is that at
runtime, the method binding need know only enough to invoke a
method. However at design time, we want to be able resolve a
method binding in such a way that we can provide the same kinds of
features we provide for properties such as signature validation and
content assist.
The JSP document processor parses JSP document models looking for
information to update in the simulated design time. The primary
objective of the processor is to allow component writers to add support
for tags that contribute EL variables. They can accomplish this by
contributing JSF tooling meta-data for a particular
uri/element/attribute that defines such a variable. The meta-data
properties that are supported are as follows:
Meta-data
Trait
|
Valid Values
|
Description
|
contributes-value-binding
|
true or false
|
This property alerts the model
processor that this attribute contributes a variable to the EL name
space at runtime. If no further meta-data is provided, this
will cause a default variable using the text of the attribute as the
name to be added to the name space for this document at 'request'
scope. The variable will have no properties or
methods. More information about the variable can be provided
using the extra meta-data defined below.
|
value-binding-scope
|
'request', 'session',
'application'
|
This property will set the
runtime scope for the contribute variable. The default is 'request'
if not provided.
|
value-binding-symbol-factory
|
An corresponding to a
'factoryId' field on a valid extension of 'org.eclipse.jst.jsf.common.contextSymbolFactory'.
|
If you wish to customize the
variable created for this attribute, you can specify this factory
extension. Your factory will be passed all available context,
including DOM context, with which you can decide how to create a
custom symbol for your variable. See Contributing EL Variables for more details.
|
|
optional-value-binding-static-type
From 3.0
|
Must be of the form "Ljava.lang.String;". See the
JDT Signature class for more information |
A java signature that suggests a static type for the
resulting symbol. Optional.
|
|
optional-value-binding-valueexpr-attr
From 3.0
|
Must be the name of an attribute on the same element. |
The name of the attribute on the same element that will hold a value expression whose type will be used as the type of the resulting symbol. Optional.
|
Loadbundle example
Below is the meta-data markup for the built-in core loadBundle variable
contributor meta-data:
<entity id="loadBundle">
<entity id="var">
<trait id="contributes-value-binding">
<value>true</value>
</trait>
<trait id="value-binding-scope">
<value>request</value>
</trait>
<trait id="value-binding-symbol-factory">
<value>org.eclipse.jst.jsf.designtime.core.loadBundle</value>
</trait>
</entity>
</entity>
This fragment defines meta-data for the attribute 'var' of tag
element 'loadBundle' (the uri for the tag library is declared in the
extension point). The meta-data tells the processor to add a
variable with scope 'request' using the factory defined by the extension
factory id 'org.eclipse.jst.jsf.designtime.core.loadBundle'.
Other Information
