Contributing EL Variables
The JSF tooling provides three ways to contribute EL variables to the framework depending on your goal.
If you are a component developer and want to add support for EL
variables that are declared by your component tags, you can use the
symbol factory extension and meta-data.
If you are a tooling developer and you wish to add new sources of
variables without changing the behavior of other sources (beans, tag
contributed variables), you can use the symbolProvider extension.
If you are a tooling developer and you wish to modify the way all
variables are resolved, you can use the variableResolver extension.
Symbol Factory Extension and Meta-data
A symbol factory is any factory class that extends
Once you create your implementation, you can declare it to the
framework using the
point. In the extension, you need to provide a unique
factoryId. This factoryId is used to identify your factory and
can then be used in your symbol factory meta-data section. See also the
Design Time Application Manager
Your factory implementation will implement the following method:
protected abstract ISymbol internalCreate(String symbolName, int scope, IAdaptable context, List problems, final IAdditionalContextSymbolInfo additionalInfo);
is the one provided by the system, usually corresponding
to the tag attribute, that declares the variable. You may use
this symbol name or ignore it and use your own, depending on how the
variable will be named at runtime. The scope
argument is one of
ISymbolConstants.SYMBOL_SCOPE_*. The system value is passed in
based on meta-data settings if present. Your factory is not
obligated to use this scope variable. The IAdaptable context
object provides context information about the source of the variable
declaration. This is usually an IModelContext object. You
can implement the supports() abstract method in such a way to tell the
framework what types of context object you support.
list is for future use. In future versions, you will
be able to add diagnostic objects to the list that report warnings or
errors related to symbol creation. Currently, the list is ignored. The additionalInfo interface (if non-null) contains optional information provided to the framework about how to construct on an object
Simplified Symbol Context Factories
Starting in WTP 3.0, several default symbol factories have been added for common tasks.
These new factories can be used by specifying their factory ids (see
JSP model processor). The following are the new ids with an explanation of their function:
||Creates a statically-typed Java symbol based on the type signature passed using optional-value-binding-static-type meta-data value.
||Creates a new symbol, using the attribute on the current tag specified by optional-value-binding-valueexpr-attr to extract type information from an EL expression.
||Creates a new symbol with an unknown type that effectively allows all properties as valid.
Deprecation note: Prior to WTP release 3.0 (Ganymede train), the method:
protected abstract ISymbol internalCreate(String symbolName, int scope, IAdaptable context, List problems);
was used for this API. This method is now deprecated in favor of the new method that takes the IAdditionalContextSymbolInfo object. Existing code is still backward compatible and is the equivalent of calling the new method with null for the additionalInfo argument. You can migrate to the new method by simply implementing it instead and ignoring the additionalInfo argument which is always optional.
JSF has many ways to contribute variables. If the framework has
overlooked any or if you have added new ways yourself without affecting
the way other variables, such as managed beans, are declared, then you
can do so through the
extension. Your symbol provider will implement the
interface. Every time the framework requests a list of variables
through the default VariableResolver and ExternalContext, your provider
will be queried for all its symbols at one or more scopes.
Note that your symbol provider may not called if:
- the default variable resolver has been replaced by one that does not call the default external context.
- the default external context has been replaced by one that does not query the symbol providers.
The variable provider extension allows you to register your own design
time resolver. You declare your resolver using the
org.eclipse.jst.jsf.core.variableresolver extension point.
Your extension will declare a unique id and a class. The class
To register your resolver as the active one for a project (note: JSF
1.1 only supports a single variable resolver at a given time.
Future versions supporting JSF 1.2 will have a more robust scheme
matching what is defined in the newer specification), you use
DesignTimeApplicationManager.setVariableResolverProvider specifying the
id defined in your extension as the argument.
Once your variable resolver is registered and active for a project, all
variable resolution requests to the framework will call your
implementation. This gives you complete control over how all EL
variable symbols are discovered and instantiated by the design time
Starting in WTP 3.0, Variable and Property Resolvers support a decorative mechanism for adding
variables and properties. By setting the forRuntimeClass on the extension for these resolvers
you can cause the resolver to only be consulted if the runtime class specified is found in the
application configuration. This allows the design time to behave similar to the runtime which
allows decorative chaining of variable and property resolvers. See
org.eclipse.jst.jsf.core.variableresolver extension point. for more information.
Starting in WTP 3.0, Variable and Property Resolvers can be declared as being constructed on per-project
basis instead of the (default) per-workspace convention. See the entension point docs on instancePerProject value
for more information.