如何检查JSTL中的isNumeric/isNumber? [英] How to check isNumeric / isNumber in JSTL?

问题描述

如何在JSTL中进行此简单检查(不扩展任何Java类和其他JSP函数).我需要这样:

How to do this simple check in JSTL (without extending any Java classes and additional JSP functions). I need it like this:

<c:if test="${fn:isNumeric()}">
    // do something
</c:if>

先谢谢了.

推荐答案

如果您的环境支持在EL对象上调用非getter方法的新EL 2.2功能(在所有与Servlet 3.0兼容的容器中都可用，例如Tomcat 7) ，Glassfish 3等)，那么您可以只使用

If your environment supports the new EL 2.2 feature of invoking non-getter methods on EL objects (which is available in all Servlet 3.0 compatible containers, such as Tomcat 7, Glassfish 3, etc), then you could just use the String#matches() method directly in EL.

<c:set var="numberAsString">${someExpressionToTestForNumber}</c:set>
<c:if test="${numberAsString.matches('[0-9]+')}">
    It's a number!
</c:if>

(我将减号-以及千位和分数分隔符,和.排除在可能的字符之外，这些字符可能会以技术上有效的数字出现)

(I'll leave the minus - and the thousands and fraction separators , and . outside consideration as possible characters which may appear in a technically valid number)

请注意，带有 body 表达式的<c:set>使用String#valueOf()隐式将任何类型转换为String.否则，对于非String类型的<c:if>中的matches()调用将失败.

Note that the <c:set> with the expression in its body implicitly converts any type to String using String#valueOf(). Otherwise the matches() call in <c:if> would fail for non-String types.

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