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The Java EE 6 Tutorial: Basic Concepts in Java Creation barcode 3 of 9 in Java The Java EE 6 Tutorial: Basic Concepts




How to generate, print barcode using .NET, Java sdk library control with example project source code free download:
The Java EE 6 Tutorial: Basic Concepts using barcode creation for servlet control to generate, create code 3 of 9 image in servlet applications. itf-14 Immediate and Deferred Evaluation Syntax Because of its multiphase lifecycle, JavaServer Faces technology uses mostly deferred evaluation expressions. During the lifecycle, component events are handled, data is validated, and other tasks are performed in a particular order. Therefore, a JavaServer Faces implementation must defer evaluation of expressions until the appropriate point in the lifecycle.

Other technologies using the EL might have different reasons for using deferred expressions.. Immediate Evaluation All expression s using the ${} syntax are evaluated immediately. These expressions can be used only within template text or as the value of a tag attribute that can accept runtime expressions. The following example shows a tag whose value attribute references an immediate evaluation expression that gets the total price from the session-scoped bean named cart:.

<fmt:formatNumber value="${sessionScope.cart.total}"/> The JavaServer Faces implementation evaluates the expression ${sessionScope.cart.total}, converts it, and passes the returned value to the tag handler.

Immediate evaluation expressions are always read-only value expressions. The preceding example expression cannot set the total price, but instead can only get the total price from the cart bean..

Deferred Evaluation Deferred evalu ation expressions take the form #{expr} and can be evaluated at other phases of a page lifecycle as defined by whatever technology is using the expression. In the case of JavaServer Faces technology, its controller can evaluate the expression at different phases of the lifecycle, depending on how the expression is being used in the page. The following example shows a JavaServer Faces inputText tag, which represents a text field component into which a user enters a value.

The inputText tag s value attribute references a deferred evaluation expression that points to the name property of the customer bean:. <h:inputText id="name" value="#{customer.name}" /> 6 Expression Language Value and Method Expressions For an initial request of the page containing this tag, the JavaServer Faces implementation evaluates the #{customer.name} expression during the render-response phase of the lifecycle. During this phase, the expression merely accesses the value of name from the customer bean, as is done in immediate evaluation.

For a postback request, the JavaServer Faces implementation evaluates the expression at different phases of the lifecycle, during which the value is retrieved from the request, validated, and propagated to the customer bean. As shown in this example, deferred evaluation expressions can be. Value expressions that can be used to both read and write data Method expressions Value expressi ons (both immediate and deferred) and method expressions are explained in the next section.. Value and Method Expressions The EL defines two kinds of expressions: value expressions and method expressions. Value expressions can either yield a value or set a value. Method expressions reference methods that can be invoked and can return a value.

. Value Expressions Value expressi ons can be further categorized into rvalue and lvalue expressions. Rvalue expressions can read data but cannot write it. Lvalue expressions can both read and write data.

All expressions that are evaluated immediately use the ${} delimiters and are always rvalue expressions. Expressions whose evaluation can be deferred use the #{} delimiters and can act as both rvalue and lvalue expressions. Consider the following two value expressions:.

${customer.nam jboss barcode code39 e} #{customer.name}.

The former use s immediate evaluation syntax, whereas the latter uses deferred evaluation syntax. The first expression accesses the name property, gets its value, adds the value to the response, and gets rendered on the page. The same can happen with the second expression.

However, the tag handler can defer the evaluation of this expression to a later time in the page lifecycle, if the technology using this tag allows.. The Java EE 6 Tutorial: Basic Concepts Value and Method Expressions In the case of barcode 3/9 for Java JavaServer Faces technology, the latter tag s expression is evaluated immediately during an initial request for the page. In this case, this expression acts as an rvalue expression. During a postback request, this expression can be used to set the value of the name property with user input.

In this case, the expression acts as an lvalue expression..
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