Java正则表达式验证
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Java Regular expression validation
提问by user3518223
I want to validate a string which allows only alpha numeric values and only one dot character and only underscore character in java .
我想验证一个字符串，它只允许字母数字值和 java 中只允许一个点字符和下划线字符。
String fileName = (String) request.getParameter("read");
I need to validate the fileName retrieving from the request and should satisfy the above criteria
我需要验证从请求中检索的 fileName 并且应该满足上述条件
I tried in "^[a-zA-Z0-9_'.']*$", but this allows more than one dot character
我试过了"^[a-zA-Z0-9_'.']*$"，但这允许多个点字符
I need to validate my string in the given scenarios ,
我需要在给定的场景中验证我的字符串，
1 . Filename contains only alpha numeric values . 2 . It allows only one dot character (.) , example : fileRead.pdf , fileWrite.txt etc 3 . it allows only underscore characters . All the other symbols should be declined
1 . 文件名仅包含字母数字值。2 . 它只允许一个点字符 (.) ，例如： fileRead.pdf 、 fileWrite.txt 等 3 。它只允许下划线字符。应拒绝所有其他符号
Can any one help me on this ?
谁可以帮我这个事 ？
采纳答案by Valentin Genevrais
You should use String.matches()method :
您应该使用String.matches()方法：
System.out.println("My_File_Name.txt".matches("\w+\.\w+"));
You can also use java.util.regexpackage.
您还可以使用java.util.regex包。
java.util.regex.Pattern pattern =
java.util.regex.Pattern.compile("\w+\.\w+");
java.util.regex.Matcher matcher = pattern.matcher("My_File_Name.txt");
System.out.println(matcher.matches());
For more information about REGEX and JAVA, look at this page : https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html
有关REGEX 和 JAVA 的更多信息，请查看此页面：https: //docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html
回答by ahmetcetin
You can first check the special characters which have the number limits. Here is the code:
您可以先检查有数量限制的特殊字符。这是代码：
int occurance = StringUtils.countOccurrencesOf("123123..32131.3", ".");
or
或者
int count = StringUtils.countMatches("123123..32131.3", ".");
If it does not match your request you can discard it before regex check. If there is no problem you can now put your String to alphanumeric value check.
如果它与您的请求不匹配，您可以在正则表达式检查之前将其丢弃。如果没有问题，您现在可以将字符串进行字母数字值检查。
回答by Tim Biegeleisen
You could use two negative lookaheads here:
您可以在这里使用两个负面的前瞻：
^((?!.*\..*\.)(?!.*_.*_)[A-Za-z0-9_.])*$
Each lookahead asserts that either a dot or an underscore does notoccur two times, implying that it can occur at most once.
每个先行断言，无论是点或下划线并不会出现两次，这意味着它可以最多出现一次。
It wasn't completely clear whether you requireone dot and/or underscore. I assumed not, but my regex could be easily modified to this requirement.
不完全清楚您是否需要一个点和/或下划线。我假设不是，但我的正则表达式可以很容易地修改为这个要求。
