replace substrings in string using regex groups

Question

I can't find the correct way to remove substrings case insensitive equals to "null" and replacing them with an empty string against a huge input data string, which contains many lines and uses ; as a separator.

To simplify here is an example of what I am looking for:

Input string

Steve;nuLL;2;null\n
null;nullo;nUll;Marc\n
....

Expected Output

Steve;;2;\n
;nullo;;Marc\n
...

Code

Matcher matcher = Pattern.compile("(?i)(^|;)(null)(;|$)").matcher(dataStr);
StringBuffer sb = new StringBuffer();
while (matcher.find()) {
    matcher.appendReplacement(sb, matcher.group(1) + "" + matcher.group(3));
}
return sb.toString();

Can this be solved by using regex?

EDIT:

From the java code above I only get the first match ever being replaced, but not every appearance in the line and in the data stream. For whatever reason the matcher.find() is only executed once.

Answer 1

return dataStr.replaceAll("(?smi)\\bnull\\b", "");

• \\b is the word boundary.
• (?i) is a command with i=ignore case.
• ( (?s) is DOT_ALL, . matching newline characters too.)
• (?m) is MULTI_LINE.

---

You forgot appendTail , for all after the last replacement. If the string contains more than one line, add the MULTI_LINE option for reinterpretation of ^ and $ . See the javadoc of Pattern .

while (matcher.find()) {
    matcher.appendReplacement(sb, matcher.group(1) + "" + matcher.group(3));
}
matcher.appendTail(sb);

Alternatively with lambda:

String result = matcher.replaceAll(mr -> mr.group(1) + mr.group(3));

where mr is a freely named MatchResult provided by replaceAll .

Answer 2

你可能什么来代替null ，只要它后面是一些字符，如：

first.replaceAll("(?i)(null)(?=[;$\\\n])", "")

Answer 3

You don't need anything fancy:

str = str.replaceAll("(?i)\\bnull\\b", "");

(?1) means "ignore case". \\b means "word boundary". Embedded newlines are irrelevant.