Java 中正则表达式如何匹配竖线(|)
在Java中直接调用String的split方法:
val b = java.lang.String(a)
val s3 = b.split("|") // ["a","b","c","|","1","2","3","4"]
println(JSON.toJSONString(s3))
因为 | 在正则表达式中是或的概念,要想匹配就得用转移字符 "|" 但是 "" 又是java的转移字符,要让其在正则中起作用,就得使用: "\|"
val b = java.lang.String(a)
val s3 = b.split("|")
println(JSON.toJSONString(s3)) // ["a","b","c","|","1","2","3","4"]
val s4 = b.split("\\|")
println(JSON.toJSONString(s4)) // ["abc","1234"]
这个Java 中的 split 方法设计简直就是一个"天坑"(天然的坑): 如果不看实现代码,很容易犯错.
public String[] split(String regex) {
return split(regex, 0);
}
public String[] split(String regex, int limit) {
/* fastpath if the regex is a
(1)one-char String and this character is not one of the
RegEx's meta characters ".$|()[{^?*+\\", or
(2)two-char String and the first char is the backslash and
the second is not the ascii digit or ascii letter.
*/
char ch = 0;
if (((regex.value.length == 1 &&
".$|()[{^?*+\\".indexOf(ch = regex.charAt(0)) == -1) ||
(regex.length() == 2 &&
regex.charAt(0) == '\\' &&
(((ch = regex.charAt(1))-'0')|('9'-ch)) < 0 &&
((ch-'a')|('z'-ch)) < 0 &&
((ch-'A')|('Z'-ch)) < 0)) &&
(ch < Character.MIN_HIGH_SURROGATE ||
ch > Character.MAX_LOW_SURROGATE))
{
int off = 0;
int next = 0;
boolean limited = limit > 0;
ArrayList<String> list = new ArrayList<>();
while ((next = indexOf(ch, off)) != -1) {
if (!limited || list.size() < limit - 1) {
list.add(substring(off, next));
off = next + 1;
} else { // last one
//assert (list.size() == limit - 1);
list.add(substring(off, value.length));
off = value.length;
break;
}
}
// If no match was found, return this
if (off == 0)
return new String[]{this};
// Add remaining segment
if (!limited || list.size() < limit)
list.add(substring(off, value.length));
// Construct result
int resultSize = list.size();
if (limit == 0) {
while (resultSize > 0 && list.get(resultSize - 1).length() == 0) {
resultSize--;
}
}
String[] result = new String[resultSize];
return list.subList(0, resultSize).toArray(result);
}
return Pattern.compile(regex).split(this, limit);
}
在Kotlin 中, 直接优化了这个 split 方法:
val a = "abc|1234"
val s1 = a.split("|")
val s2 = a.split("\\|")
println(s1) // [abc, 1234]
println(s2) // [abc|1234]