Remove all whitespaces from String but keep ONE newline
java, removing-whitespace, string, whitespace
Solution
In a single regex (plus a small patch for tabs):
input.replaceAll("^\\s+|\\s+$|\\s*(\n)\\s*|(\\s)\\s*", "$1$2")
.replace("\t"," ");
The regex looks daunting, but in fact decomposes nicely into these parts that are OR-ed together:
- `^\s+` – match whitespace at the beginning;
- `\s+$` – match whitespace at the end;
- `\s*(\n)\s*` – match whitespace containing a newline, and capture that newline;
- `(\s)\s*` – match whitespace, capturing the first whitespace character.
The result will be a match with two capture groups, but only one of the groups may be non-empty at a time. This allows me to replace the match with `"$1$2"`, which means "concatenate the two capture groups."
The only remaining problem is that I can't replace a tab with a space using this approach, so I fix that up with a simple non-regex character replacement.
Problem
I have this input String (containg tabs, spaces, linebreaks): ``` That is a test. seems to work pretty good? working. Another test again. ``` [Edit]: I should have provided the String for better testing as stackoverflow removes all special characters (tabs, ...) ``` String testContent = "\n\t\n\t\t\t\n\t\t\tDas ist ein Test.\t\t\t \n\tsoweit scheint das \t\tganze zu? funktionieren.\n\n\n\n\t\t\n\t\t\n\t\t\t \n\t\t\t \n \t\t\t\n \tNoch ein Test.\n \t\n \t\n \t"; ``` And I want to reach this state: ``` That is a test. seems to work pretty good? working. Another test again. ``` ``` String expectedOutput = "Das ist ein Test.\nsoweit scheint das ganze zu? funktionieren.\nNoch ein Test.\n"; ``` Any ideas? Can this be achieved using regexes? `replaceAll("\\s+", " ")` is NOT what I'm looking for. If this regex would preserve exactly 1 newline of the ones existing it would be perfect. I have tried this but this seems suboptimal to me...: ``` BufferedReader bufReader = new BufferedReader(new StringReader(testContent)); String line = null; StringBuilder newString = new StringBuilder(); while ((line = bufReader.readLine()) != null) { String temp = line.replaceAll("\\s+", " "); if (!temp.trim().equals("")) { newString.append(temp.trim()); newString.append("\n"); } } ```