如何比较 EL 中的字符属性 [英] How to compare a char property in EL

问题描述

我有一个如下所示的命令按钮.

I have a command button like below.

<h:commandButton value="Accept orders" action="#{acceptOrdersBean.acceptOrder}"
   styleClass="button" rendered="#{product.orderStatus=='N' }"></h:commandButton>

即使 product.orderStatus 值等于 'N' 命令按钮也不会显示在我的页面中.

even when the product.orderStatus value is equal to 'N' the command button is not displayed in my page.

这里的 product.orderStatus 是一个字符属性.

Here product.orderStatus is a character property.

推荐答案

不幸的是，这是预期的行为.在 EL 中，诸如 'N' 之类的引号中的任何内容总是被视为 String，而 char 属性值总是被视为数字.char 在 EL 中由其 Unicode 代码点表示，即 78 代表 N.

This is, unfortunately, expected behavior. In EL, anything in quotes like 'N' is always treated as a String and a char property value is always treated as a number. The char is in EL represented by its Unicode codepoint, which is 78 for N.

有两种解决方法:

1. 使用String#charAt()，传递0，从String中取出char代码> EL.请注意，这仅在您的环境支持 EL 2.2 时才有效.否则，您需要安装 JBoss EL.

1. Use String#charAt(), passing 0, to get the char out of a String in EL. Note that this works only if your environment supports EL 2.2. Otherwise you need to install JBoss EL.

<h:commandButton ... rendered="#{product.orderStatus eq 'N'.charAt(0)}">

使用字符在 Unicode 中的数字表示，即 N 为 78.您可以通过 System.out.println((int) 'N') 找出正确的 Unicode 代码点.

Use the char's numeric representation in Unicode, which is 78 for N. You can figure out the right Unicode codepoint by System.out.println((int) 'N').

<h:commandButton ... rendered="#{product.orderStatus eq 78}">

真正的解决方案是使用 枚举:

public enum OrderStatus {
     N, X, Y, Z;
}

与

private OrderStatus orderStatus; // +getter

然后你就可以在 EL 中准确使用所需的语法:

then you can use exactly the desired syntax in EL:

<h:commandButton ... rendered="#{product.orderStatus eq 'N'}">

额外的好处是枚举强制类型安全.您将无法指定像 ☆ 或 웃 这样的任意字符作为订单状态值.

Additional bonus is that enums enforce type safety. You won't be able to assign an aribtrary character like ☆ or 웃 as order status value.

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