使用正则表达式替换两个定界符之间的所有字符

Question

I'm trying to replace all characters between two delimiters with another character using regex. The replacement should have the same length as the removed string.

String string1 = "any prefix [tag=foo]bar[/tag] any suffix";
String string2 = "any prefix [tag=foo]longerbar[/tag] any suffix";
String output1 = string1.replaceAll(???, "*");
String output2 = string2.replaceAll(???, "*");

The expected outputs would be:

output1: "any prefix [tag=foo]***[/tag] any suffix"  
output2: "any prefix [tag=foo]*********[/tag] any suffix"

I've tried "\\\\\\\\\\[tag=.\\*?](.\\*?)\\\\\\\\[/tag]" but this replaces the whole sequence with a single "\\*" .
I think that "(.\\*?)" is the problem here because it captures everything at once.

How would I write something that replaces every character separately?

Answer 1

you can use the regex

\w(?=\w*?\[)

which would match all characters before a "[\\"

see the regex demo , online compiler demo

Answer 2

You can capture the chars inside, one by one and replace them by * :

public static String replaceByStar(String str) {
    String pattern = "(.*\\[tag=.*\\].*)\\w(.*\\[\\/tag\\].*)";
    while (str.matches(pattern)) {
        str = str.replaceAll(pattern, "$1*$2");
    }
    return str;
}

Use like this it will print your tx2 expected outputs :

public static void main(String[] args) {
    System.out.println(replaceByStar("any prefix [tag=foo]bar[/tag] any suffix"));
    System.out.println(replaceByStar("any prefix [tag=foo]loooongerbar[/tag] any suffix"));
}

---

So the pattern "(.*\\\\[tag=.*\\\\].*)\\\\w(.*\\\\[\\\\/tag\\\\].*)" :

• (.*\\\\[tag=.*\\\\].*) capture the beginning, with eventually some char in the middle
• \\\\w is for the char you want to replace
• (.*\\\\[\\\\/tag\\\\].*) capture the end, with eventually some char in the middle

---

The substitution $1*$2 :

The pattern is (text$1)oneChar(text$2) and it will replace by (text$1)*(text$2)