电子邮件验证-@ 之前和点之前的字符长度 [英] Email validation- characters length before @ and before dot

问题描述

我使用以下正则表达式模式来验证工作正常的电子邮件地址，但是我需要验证 @ 之前的字符长度，这应该 NOT 少于 4 个字符.我应该为 @ 之后和点 . 之前的字符长度设置相同的规则.

I use the following regex pattern for validating the email address that works fine, BUT I need to validate the length of characters before @, which should NOT be less than 4 characters. The same rule I should put for the length of characters after @ and before dot ..

例如，此电子邮件地址无效:a@b.c

For example, this email address is NOT valid: a@b.c

但是，这个应该是有效的:[e-mail]

However, this one should be valid: [e-mail]

我该怎么做?

这是我目前的尝试:

<ui:define name="validation-tag">
    <f:validateRegex 
        pattern="([w.-]*[a-zA-Z0-9_]@[w.-]*[a-zA-Z0-9].[a-zA-Z][a-zA-Z.]*[a-zA-Z])*"
        for="contactEmailAddress" />
</ui:define>

推荐答案

我们可以使用带有锚点的正向预测来施加长度限制.

We can impose length restrictions using positive look-aheads with anchors.

^(?=[^@]{4,}@)([w.-]*[a-zA-Z0-9_]@(?=.{4,}.[^.]*$)[w.-]*[a-zA-Z0-9].[a-zA-Z][a-zA-Z.]*[a-zA-Z])$

^ 和 $ 将使字符串在开始和结束处匹配，然后 (?=[^@]{4,}@) 将确保我们在第一个 @ 之前至少有 4 个字符，而 (?=.{4,}.[^.]*$) 将使确保最后一个 之前的部分. 至少有 4 个符号长.

The ^ and $ will make the string match at start and end, then (?=[^@]{4,}@) will make sure we have at least 4 characters before the first @, and (?=.{4,}.[^.]*$) will make sure the part before the last . is at least 4 symbols long.

参见演示

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