Executing and object's method from EL

Question

How do I call an object's method from EL?

Give the object:

public class TestObj {
   public testObj() { };

   public String test() { return "foo"; }
   public String someOtherMethod(String param) { return param + "_bar"; } 
}

and the obj is added to the pageContext

pageContext.setAttribute("t", new TestObj());

How would I perform the equivalent of:

<%= t.test() %>
<%= t.someOtherMethod("foo") %>

using EL?

Answer 1

It's supported since EL 2.2 which has been out since December 10, 2009 (over 2.5 years ago already!). EL 2.2 goes hand in hand with Servlet 3.0, so if you target a Servlet 3.0 container (Tomcat 7, Glassfish 3, etc) with a Servlet 3.0 compatible web.xml which look like follows

<?xml version="1.0" encoding="UTF-8"?>
<web-app 
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd"
    version="3.0">

    <!-- Config here. -->

</web-app>

then you'll be able to invoke methods with or without arguments in EL in the following forms:

${t.test()}
${t.someOtherMethod('foo')}

Answer 2

According to this Method calls in EL method calls in Expression Language are currently in JSR status and not implemented yet. What I use is JST facilities for JavaBean components to do some invocations. For example, if you modify your test method signature to:

public class TestObj {
    public TestObj() { };

    public String getTest() { return "foo"; }
}

You can invoke getTest() method with this syntax:

${t.test}

Now, if you need something more elaborate -like with parameter passing- you could use Custom Method features that EL offer. That requires public static methods declared in a public class, and also a TLD file. A nice tutorial can be found here.

Update:

As @BalusC states, later specifications now support method invocations. If you're deploying to a Java EE 6 compatible container, this Oracle Site shows how to properly use the feature.