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 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]

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