[英]generating a regular expression from a string
I wish to generate a regular expression from a string containing numbers, and then use this as a Pattern to search for similar strings. 我希望从包含数字的字符串生成正则表达式,然后将其用作模式来搜索类似的字符串。 Example:
例:
String s = "Page 3 of 23"
If I substitute all digits by \\d
如果我用
\\d
替换所有数字
StringBuilder sb = new StringBuilder();
for (int i = 0; i < s.length(); i++) {
char c = s.charAt(i);
if (Character.isDigit(c)) {
sb.append("\\d"); // backslash d
} else {
sb.append(c);
}
}
Pattern numberPattern = Pattern.compile(sb.toString());
// Pattern numberPattern = Pattern.compile("Page \d of \d\d");
I can use this to match similar strings (eg "Page 7 of 47"
). 我可以用它来匹配类似的字符串(例如
"Page 7 of 47"
)。 My problem is that if I do this naively some of the metacharacters such as (){}-
, etc. will not be escaped. 我的问题是,如果我天真地这样做,一些元字符,如
(){}-
等将不会被转义。 Is there a library to do this or an exhaustive set of characters for regular expressions which I must and must not escape? 是否有一个库可以执行此操作,或者是正则表达式的详尽字符集,我必须且不能逃避? (I can try to extract them from the Javadocs but am worried about missing something).
(我可以尝试从Javadocs中提取它们,但我担心会遗漏一些东西)。
Alternatively is there a library which already does this (I don't at this stage want to use a full Natural Language Processing solution). 或者有一个已经这样做的库(我现在不想使用完整的自然语言处理解决方案)。
NOTE: @dasblinkenlight's edited answer now works for me! 注意:@ dasblinkenlight编辑的答案现在适合我!
Java's regexp library provides this functionality: Java的regexp库提供了这个功能:
String s = Pattern.quote(orig);
The "quoted" string will have all its metacharacters escaped. “引用”字符串将使其所有元字符都被转义。 First, escape your string, and then go through it and replace digits by
\\d
to make a regular expression. 首先,转义你的字符串,然后遍历它并用
\\d
替换数字来制作正则表达式。 Since regex library uses \\Q
and \\E
for quoting, you need to enclose your portion of regex in inverse quotes of \\E
and \\Q
. 由于正则表达式库使用
\\Q
和\\E
进行引用,因此需要将正则表达式的部分用\\E
和\\Q
反引号括起来。
One thing I would change in your implementation is the replacement algorithm: rather than replacing character-by-character, I would replace digits in groups. 我将在实现中改变的一件事是替换算法:我会替换组中的数字,而不是逐字符替换。 This would let an expression produced from
Page 3 of 23
match strings like Page 13 of 23
and Page 6 of 8
. 这将使得从
Page 3 of 23
Page 13 of 23
和Page 6 of 8
Page 13 of 23
Page 6 of 8
生成的表达式匹配。
String p = Pattern.quote(orig).replaceAll("\\d+", "\\\\E\\\\d+\\\\Q");
This would produce "\\QPage \\E\\d+\\Q of \\E\\d+\\Q\\E"
no matter what page numbers and counts were there originally. 无论最初的页码和计数是什么,这都会产生
"\\QPage \\E\\d+\\Q of \\E\\d+\\Q\\E"
。 The output needs only one, not two slashes in \\d
, because the result is fed directly to regex engine, bypassing the Java compiler. 输出在
\\d
只需要一个而不是两个斜杠,因为结果直接送到regex引擎,绕过Java编译器。
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