The createMethodExpression(ELContext, String, Class, Class[]) method can be used to parse an expression string and return a concrete instance of MethodExpression that encapsulates the parsed expression. The FunctionMapper is used at parse time, not evaluation time, so one is not needed to evaluate an expression using this class. However, the ELContext is needed at evaluation time.

The getMethodInfo(ELContext) and invoke(ELContext, Object[]) methods will evaluate the expression each time they are called. The ELResolver in the ELContext is used to resolve the top-level variables and to determine the behavior of the . and [] operators. For any of the two methods, the getValue(ELContext, Object, Object) method is used to resolve all properties up to but excluding the last one. This provides the base object on which the method appears. If the base object is null, a PropertyNotFoundException must be thrown. At the last resolution, the final property is then coerced to a String, which provides the name of the method to be found. A method matching the name and expected parameters provided at parse time is found and it is either queried or invoked (depending on the method called on this MethodExpression).

See the notes about comparison, serialization and immutability in the Expression javadocs.