问题描述
在Java中,如何确定String是否与(即:歌曲%03d.mp3
)?
In Java, how can you determine if a String matches a format string (ie: song%03d.mp3
)?
换句话说,如何你会实现以下函数吗?
In other words, how would you implement the following function?
/**
* @return true if formatted equals String.format(format, something), false otherwise.
**/
boolean matches(String formatted, String format);
示例:
matches("hello world!", "hello %s!"); // true
matches("song001.mp3", "song%03d.mp3"); // true
matches("potato", "song%03d.mp3"); // false
也许有办法将格式字符串转换为正则表达式?
Maybe there's a way to convert a format string into a regex?
格式String是一个参数。我不提前知道。 song%03d.mp3
只是一个例子。它可以是任何其他格式字符串。
The format String is a parameter. I don't know it in advance. song%03d.mp3
is just an example. It could be any other format string.
如果有帮助,我可以假设格式字符串只有一个参数。
If it helps, I can assume that the format string will only have one parameter.
推荐答案
我不知道这样做的库。以下是如何将格式模式转换为正则表达式的示例。请注意, Pattern.quote
对于处理格式字符串中的意外正则表达非常重要。
I don't know of a library that does that. Here is an example how to convert a format pattern into a regex. Notice that Pattern.quote
is important to handle accidental regexes in the format string.
// copied from java.util.Formatter
// %[argument_index$][flags][width][.precision][t]conversion
private static final String formatSpecifier
= "%(\\d+\\$)?([-#+ 0,(\\<]*)?(\\d+)?(\\.\\d+)?([tT])?([a-zA-Z%])";
private static final Pattern formatToken = Pattern.compile(formatSpecifier);
public Pattern convert(final String format) {
final StringBuilder regex = new StringBuilder();
final Matcher matcher = formatToken.matcher(format);
int lastIndex = 0;
regex.append('^');
while (matcher.find()) {
regex.append(Pattern.quote(format.substring(lastIndex, matcher.start())));
regex.append(convertToken(matcher.group(1), matcher.group(2), matcher.group(3),
matcher.group(4), matcher.group(5), matcher.group(6)));
lastIndex = matcher.end();
}
regex.append(Pattern.quote(format.substring(lastIndex, format.length())));
regex.append('$');
return Pattern.compile(regex.toString());
}
当然,实施 convertToken
将是一个挑战。下面是一些事情:
Of course, implementing convertToken
will be a challenge. Here is something to start with:
private static String convertToken(String index, String flags, String width, String precision, String temporal, String conversion) {
if (conversion.equals("s")) {
return "[\\w\\d]*";
} else if (conversion.equals("d")) {
return "[\\d]{" + width + "}";
}
throw new IllegalArgumentException("%" + index + flags + width + precision + temporal + conversion);
}
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