What does com.sun.el package contain?

Question

Is this just an API defined by Java, to be implemented by (say) servers, or the JRE includes the implementation too?

Thing is that I was trying to concatenate two strings using '+' on my JSF page, but it threw NumberFormatException. It seems it was trying to parse my strings using Long.parseLong().

I was surprised to see this package in the stack trace, as I was thought these expressions are Groovy expressions. This certainly doesn't seem to be Groovy but some other EL.

I am using Weblogic server.

Answer 1

It contains Sun's implementation of the javax.el API which is specified by EL specification. This API is part of Java EE, not Java SE. Implementors are required to provide a concrete implementation of the abstract API so that all the API-definied works will be done. Java EE is basically one large abstract specification. The servletcontainers / applicationservers like Weblogic, Tomcat, Glassfish, etc offers the concrete implementations.

As to your actual problem, no, you indeed can't concatenate strings in EL using + operator like that. The + operator in EL assumes the both sides to be a Number, for round numbers that's Long. That's specified in the EL specification.

You can however just use multiple expressions like follows to "concat" strings.

<h:outputText value="#{user.firstName} #{user.lastName}" />