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可以正常工作的电子邮件地址，但我需要验证@之前的字符长度，该字符长度应不能少于4个字符.对于@之后和点.之前的字符长度，我应该使用相同的规则.

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有效: a@b.c

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

但是，这应该是有效的: [e-mail]

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

我该怎么办?

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提前强加长度限制.

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$将使字符串在开头和结尾处都匹配，然后(?=[^@]{4,}@)将确保我们在第一个@之前至少有4个字符，而(?=.{4,}\.[^.]*$)将确保该部分最后一个.之前的长度至少为4个符号.

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.

请参见演示

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