Tuesday Sep 24, 2013

Session Report: JSR 341: Expression Language 3.0

Ed Burns, Consulting Member of Technical Staff, and Kinman Chung, Principle Member of Technical Staff, both at Oracle, presented a session on Monday in which they described new features in JSR 341, Expression Language (EL) 3.0. They discussed the APIs for the use of EL in standalone environments and EL syntax for new operators, plus lambda expressions, and support for collection objects, all the while offering copious code illustrations.

Burns remarked that he was pleased that Java Champion and JavaOne Rock Star Adam Bien had referred to EL 3.0 as “the hidden gem of Java EE”. “I don’t know how hidden it is,” said Burns, “but I think it’s a gem.”

He discussed the origins of EL, which has a long and active history in the Java platform. EL began in 2004 as part of the Java Standard Tag Library (JSTL 1.0), moved to JSP 2.0 in 2006, and became an independent specification with JSR 341 in 2011. It is used in JSF, CDI, and Avatar. Now, 9 years after its inception, it is an independent specification that is heavily used in JSF.   

Burns observed that the presence of EL is the key differentiator between Java server and non-java server stacks. “Java server-based web frameworks are likely to use EL,” said Burns. “When you show someone who is not familiar with EL how easy it is to move things together from disparate parts of your application, it’s very compelling.”

The most important feature that EL 3 brings is lambda expressions – developers do not have to wait until Java SE 8 is released. It all runs on Java EE 7, which requires Java SE 7 -- which means that it is currently available. Burns gave a brief discussion of lambda expressions, which basically behave like an anonymous function -- lambdas in EL are EL expressions. They offer full access to the EL environment within the body of the EL lambda expression, something not available from Java SE lambdas. “You won’t be able to refer to other EL things from a plain old SE lambda expression,” said Burns.

The goal of EL 3 is to provide greater expressive power for applications and to use it outside of Java EE. Burns and Chung provided an overview of collection operations and explained EL’s support for stand-alone environments. EL 3 is easy to use outside of Java EE and provides standard data structures: ELContext; ELResolvers; and local variable and function repositories.

They explained that it enables direct EL operations and has: EL expression evaluation; Bean definition; and Function definition. They emphasized that other key parts of Java EE can also be used standalone, such as: Bean Validation; Persistence (JPA); and Contexts and Dependency Injection (CDI). They encouraged developers to consider the possibilities for cloud deployment in: Defining functions and variables and defining beans.

They spent the rest of the session illustrating their key points with a healthy dose of code.

Links and Downloads:
* JSR 341: http://www.jcp.org/en/jsr/detail?id=341
    Download spec and API javadocs

* Project home: https://java.net/projects/el-spec/
   Report spec bugs or RFE for el.next

* RI: https://java.net/projects/uel/
   Maven artifacts available from Maven Central
   Download source and report RI bugs

* Integrated in Glassfish 4.0: https://glassfish.java.net/

You can listen to this session in early October on Parleys.com.

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