Programmatically Inspect a ValueExpression Using OmniFaces

OmniFaces comes with an entire package dedicated to manipulate EL artifacts, named org.omnifaces.el. In this post, I will focus on a class named ExpressionInspector, which can be very useful when you need to programmatically inspect a ValueExpression. One of the most important method of this class is named, getMethodReference(), and, as its name suggest, it gets a MethodReference from a ValueExpression. If the ValueExpression refers to a method, this will contain the actual method. If it refers to a property, this will contain the corresponding getter method. Via the MethodReference, we have access to several information as follows:

·         MethodReference#getBase() - Returns the base of the EL method expression. Usually, this is the backing bean on which the method behind MethodReference#getMethod() should be invoked.

·         MethodReference#getMethod() - Returns the concrete java.lang.reflect.Method instance of the EL method expression. Usually, this is a method of the class behind getBase().

·         MethodReference#getActualParameters() - Returns the actual (evaluated) parameters of the method call. If there are no params, then this returns an empty array, never null. Those should be passed to Method#invoke(Object, Object...).

·         MethodReference#isFromMethod() - Returns true if this method reference is from an actual method call and not from a getter of a property.

·         MethodReference#getMethodInfo() - Returns the standard EL MethodInfo of the MethodExpression where this MethodReference has been extracted from.

In order to have some examples, we apply the below code to several ValueExpressions:

import org.omnifaces.el.ExpressionInspector;

import org.omnifaces.el.MethodReference;

import org.omnifaces.util.Faces;

...

ELContext elc = Faces.getELContext();

ValueExpression ve = getValueExpression("value");

       

System.out.println("-------------------------ExpressionInspector------------------------------");

System.out.println("getValueExpression(\"value\"): " + ve);

MethodReference methodReference = ExpressionInspector.getMethodReference(elc, ve);

System.out.println("MethodReference#getBase(): " + methodReference.getBase());

System.out.println("MethodReference#getMethod(): " + methodReference.getMethod());

System.out.println("MethodReference#getMethodInfo()#getName(): " + methodReference.getMethodInfo().getName());

System.out.println("MethodReference#getMethodInfo()#getReturnType(): " + methodReference.getMethodInfo().getReturnType());

System.out.println("MethodReference#getMethodInfo()#getParamTypes(): ");

Class<?>[] paramTypes = methodReference.getMethodInfo().getParamTypes();

for (Class paramType : paramTypes) {

     System.out.println("Parameter info:\n name:" + paramType.getName() + ", simple name: " + paramType.getSimpleName() + ", type:" + paramType.getTypeName());

}

System.out.println("MethodReference#getActualParameters(): ");

Object[] actualParams = methodReference.getActualParameters();

for (Object actualParam : actualParams) {

     System.out.println("Actual parameter: " + actualParam);

}

System.out.println("MethodReference#isFromMethod(): " + methodReference.isFromMethod());

System.out.println("--------------------------------------------------------------------------");

·         in the first case we have a simple managed bean (PlayerBean) with a field, named atp. The inspected ValueExpression will be: #{playerBean.atp}. See below figure:

Output:

-------------------------ExpressionInspector-------------------------------

getValueExpression("value"): /index.xhtml @14,56 value="#{playerBean.atp}"

MethodReference#getBase(): atp.singles.PlayerBean@3b45398a

MethodReference#getMethod(): public java.lang.String atp.singles.PlayerBean.getAtp()

MethodReference#getMethodInfo()#getName(): getAtp

MethodReference#getMethodInfo()#getReturnType(): class java.lang.String

MethodReference#getMethodInfo()#getParamTypes():

MethodReference#getActualParameters():

MethodReference#isFromMethod(): false

---------------------------------------------------------------------------

·         next, we inspect a ValueExpression that point out a field encapsulated in another field.  The inspected ValueExpression will be: #{playerBean.player.name}. See below figure:

Output:

--------------------------ExpressionInspector-------------------------------

getValueExpression("value"): /index.xhtml @14,64 value="#{playerBean.player.name}"

MethodReference#getBase(): atp.singles.Player@5a268b

MethodReference#getMethod(): public java.lang.String atp.singles.Player.getName()

MethodReference#getMethodInfo()#getName(): getName

MethodReference#getMethodInfo()#getReturnType(): class java.lang.String

MethodReference#getMethodInfo()#getParamTypes():

MethodReference#getActualParameters():

MethodReference#isFromMethod(): false

Info:   ----------------------------------------------------------------------------

·         further, we inspect an ValueExpression that points out a managed bean method (not a getter) without arguments  that returns a String. The inspected ValueExpression will be: #{playerBean.uppercasePlayer()}. See below figure:

Output:

--------------------------ExpressionInspector-------------------------------

getValueExpression("value"): /index.xhtml @14,70 value="#{playerBean.uppercasePlayer()}"

MethodReference#getBase(): atp.singles.PlayerBean@5d8b700b

MethodReference#getMethod(): public java.lang.String atp.singles.PlayerBean.uppercasePlayer()

MethodReference#getMethodInfo()#getName(): uppercasePlayer

MethodReference#getMethodInfo()#getReturnType(): class java.lang.String

MethodReference#getMethodInfo()#getParamTypes():

MethodReference#getActualParameters():

MethodReference#isFromMethod(): true

----------------------------------------------------------------------------

·         finally, we inspect a ValueExpression representing a call of a managed bean method that receive two arguments and returns. The inspected ValueExpression will be: #{playerBean.changeRank(2, 5)}. See below figure:

Output:

--------------------------ExpressionInspector-------------------------------

getValueExpression("value"): /index.xhtml @14,69 value="#{playerBean.changeRank(2, 5)}"

MethodReference#getBase(): atp.singles.PlayerBean@253bf759

MethodReference#getMethod(): public atp.singles.Rank atp.singles.PlayerBean.changeRank(int,int)

MethodReference#getMethodInfo()#getName(): changeRank

MethodReference#getMethodInfo()#getReturnType(): class atp.singles.Rank

MethodReference#getMethodInfo()#getParamTypes():

  Parameter info:

  name:int, simple name: int, type:int

  Parameter info:

  name:int, simple name: int, type:int

MethodReference#getActualParameters():

  Actual parameter: 2

  Actual parameter: 5

MethodReference#isFromMethod(): true

Info:   ----------------------------------------------------------------------------

Enjoy!