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JSP-EL allows function references inside expressions of
the form <prefix>:<localName>(…). JSP-EL
based expression managers delegate resolution of such function references
to a function-mapper. In Java, the function-mapper is an implementation
of the javax.servlet.jsp.el.FunctionMapper interface. It is the
function-mapper’s responsibility to resolve a prefix and local-name
to a static Java function (an instance of java.lang.reflect.Method) which
the expression manager can call as part of expression evaluation.
The Expression Manager building block provides a function-mapper
implementation which is an OSGi service deployed as part of the
Expression Manager bundle. The implementation creates a registry
of functions by querying the other bundles deployed in the same
CRX container for any functions they are exporting for use inside
expressions. The prefix and local-name supplied to this function-mapper
must then be resolvable to one of the functions in this aggregated registry.
Expression Manager supports two types of functions which bundles
can export: Remote Functions: These functions resolve
to methods declared on the interfaces implemented by beans. Host
bundles export the beans as OSGi services and also over Flex remoting.
Remote functions can be called from both: the server-side
Expression Manager, since it is deployed in the same CRX container.
the client-side Expression Manager since such functions are
exposed over Flex remoting.
Remote functions
use prefixes which start with the keyword "REMOTE_".
Local Functions: These functions are local to the runtime
in which expressions are being evaluated. In Java, these functions
correspond to static functions defined on Java classes. In Flex,
these functions correspond to normal methods defined on ActionScript
classes. The Expression Manager implementation assumes symmetrical
local functions for which an implementation exists both in Java
and in Flex.
For example, there could be a logical 'str:substring(…)'
function for which the Java implementation is a static 'substring'
method defined on a 'com.adobe.exm.java.StringUtils' Java class.
While the Flex implementation is a 'substr' method defined on a
'com.adobe.exm.flex.StringUtilities' ActionScript class.
Any prefix which does not start with the "REMOTE_" keyword is
assumed to map to a local function. The Expresion Manager function-mapper
can handle both types of functions and distinguishes between them
based on whether the function prefix starts with the "REMOTE_" keyword.
This function-mapper is not available as a public class which you
can use inside Spring contexts. Instead, it is an OSGi service hosted
by the Expression Manager bundle which must be imported into the
custom Spring contexts of consuming bundles via BluePrint: <bp:reference id="<mapper_id> "
interface="javax.servlet.jsp.el.FunctionMapper"
filter="(exm.function.mapper.id=lc.exm.compositeFunctionMapper)"/>
The imported service can then be injected into the DefaultEXPEvaluator
bean configured in the custom Spring context using <mapper_id> as
a reference.
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