Materi Bahasa Inggris ( Language Expression )

language expression

Welcome

 to the English lessons on language expression

Expression Language

This chapter introduces the Expression Language (also referred to as the EL), which provides an important mechanism for enabling the presentation layer (web pages) to communicate with the application logic (managed beans). The EL is used by both JavaServer Faces technology and JavaServer Pages (JSP) technology. The EL represents a union of the expression languages offered by JavaServer Faces technology and JSP technology.

While there are several other Java expression languages available, OGNL, MVEL, and JBoss EL, to name a few, the Spring Expression Language was created to provide the Spring community with a single well supported expression language that can be used across all the products in the Spring portfolio. Its language features are driven by the requirements of the projects in the Spring portfolio, including tooling requirements for code completion support within the eclipse based Spring Tool Suite. That said, SpEL is based on a technology agnostic API allowing other expression language implementations to be integrated should the need arise.
While SpEL serves as the foundation for expression evaluation within the Spring portfolio, it is not directly tied to Spring and can be used independently. In order to be self contained, many of the examples in this chapter use SpEL as if it were an independent expression language. This requires creating a few bootstrapping infrastructure classes such as the parser. Most Spring users will not need to deal with this infrastructure and will instead only author expression strings for evaluation. An example of this typical use is the integration of SpEL into creating XML or annotated based bean definitions as shown in the section Expression support for defining bean definitions.
This chapter covers the features of the expression language, its API, and its language syntax. In several places an Inventor and Inventor’s Society class are used as the target objects for expression evaluation. These class declarations and the data used to populate them are listed at the end of the chapter.

The ExpressionLanguage Component

The ExpressionLanguage component provides an engine that can compile and evaluate expressions. An expression is a one-liner that returns a value (mostly, but not limited to, Booleans).

The purpose of the component is to allow users to use expressions inside configuration for more complex logic. For some examples, the Symfony2 Framework uses expressions in security, for validation rules and in route matching.
Besides using the component in the framework itself, the ExpressionLanguage component is a perfect candidate for the foundation of a business rule engine. The idea is to let the webmaster of a website configure things in a dynamic way without using PHP and without introducing security problems:

Expressions can be seen as a very restricted PHP sandbox and are immune to external injections as you must explicitly declare which variables are available in an expression.

Usage

The ExpressionLanguage component can compile and evaluate expressions. Expressions are one-liners that often return a Boolean, which can be used by the code executing the expression in an if statement. A simple example of an expression is 1 + 2. You can also use more complicated expressions, such as someArray[3].someMethod('bar')

The component provides 2 ways to work with expressions:

• evaluation: the expression is evaluated without being compiled to PHP;
• compile: the expression is compiled to PHP, so it can be cached and   evaluated.

The main class of the component is ExpressionLanguage

Expression Syntax

See The Expression Syntax to learn the syntax of the ExpressionLanguage component.

Passing in Variables

You can also pass variables into the expression, which can be of any valid PHP type (including objects):

This will print "Honeycrisp". For more information, see the The Expression Syntax entry, especially Working with Objects and Working with Arrays.

Caching

The component provides some different caching strategies, read more about them in Caching Expressions Using Parser Caches.

Language Expressions in context
Sheila        :	Oh, no ! It's raining cats and dogs. I don't think Shirley will turn up for this meeting.
Mina         :	But she's given us her word. And you know we can always count on Shirley to be present.
Sheila        :	I hope you are right. We need to put our heads together to plan for the trip.
Mina         :	Look, here comes Shirley. What did I tell you ? Expression A.   The action of making known one's thoughts or feelings.  ‘ the prisoners developed a dialect as an everyday means of       expression’       ‘she accepted his expressions of sympathy B.   A look on someone's face that conveys a particular emotion.   ‘a sad expression’ C.   A word or phrase, especially an idiomatic one, used to convey an idea.    ‘we have an expression, ‘You don't get owt for nowt.’’ D.   The production of something by pressing it out.    ‘essential oils obtained by distillation or expression’ E.    Genetics The appearance in a phenotype of a characteristic or effect attributed to a particular gene.   expression of the TAT gene is restricted to the parenchymal cells Thank you for reading me English lessons on language expression that I created