Replace \ and newline replace in java

Question

I am writing code to detect bad keywords in a file. Here are the steps that I follow:

Tokenize using StreamTokenizer

Use pattern matcher to find the matches

while(streamTokenizer.nextToken() != StreamTokenizer.TT_EOF){
            if(streamTokenizer.ttype == StreamTokenizer.TT_WORD) {
                String token = streamTokenizer.sval.trim().replaceAll("\\\\n", "")
                final Matcher matcher = badKeywordPattern.matcher(token)
                if(matcher.find()) { // bad tokens found
                     return true;
                }
            }
}

String token = streamTokenizer.sval.trim().replaceAll("\\\\n", "") is done to match token spanning multiple lines with \. Example:

bad\ token

However the replace is not working. Any suggestions? Any other ways to do this?

have tried this `String token = streamTokenizer.sval.trim().replaceAll("\\"+"\n", "")` — Kh.Taheri, Apr 24 '17 at 23:47
This won't work. You won't get he entire multi line token in one piece. You have to cincatenate. — user207421, Apr 25 '17 at 00:53

score 1 · Answer 1 · answered Apr 24 '17 at 23:54

Assuming you want to remove all \ placed at end of the line, along with line separator you could use replaceAll("\\\\\\R","").

To represent \ in regex (which is what replaceAll uses) we need to escape it with another \, which leaves us with \\. But since \ is also special in String literals we need to escape each of them again with another backslash which leaves us with "\\\\"
Since Java 8 we can use \R (which needs to be written as "\\R" since \ requires escaping) to represent line separators like \r \n or \r\n pair.

score 1 · Answer 2 · answered Apr 25 '17 at 00:39

1

If I understand correctly, you do not want to use regex (which is what String.replaceAll does), just do literal string replacement with String.replace, and use one fewer backslash:

String token = streamTokenizer.sval.trim().replace("\\\n", "")

answered Apr 25 '17 at 00:39

Boann

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score 0 · Answer 3 · edited May 23 '17 at 11:46

Based on @Pshemo answer, which shows you how \ & \n presented in regex, and as mentioned here. You could do it like this:

String[] tkns = streamTokenizer.sval.trim().split("\\\\\\R"); // yourString = "bad\\\ntaken"
StringBuffer token= new StringBuffer();
for (String tkn : tkns)
{
    token.append(tkn);
    //System.out.println(tkn);
}
//final Matcher matcher = badKeywordPattern.matcher(token)

Replace \ and newline replace in java

3 Answers3