Search for any given string using JAVA REGEX

Question

I am trying to write a generic method that will search a file for a given string and replace it with another string. I am using java regex for the same

patternMatcher = Pattern.compile(searchString);
while ((line = readLine()) != null) {
    Matcher regexMatcher = patternMatcher.matcher(line);
       if (regexMatcher.lookingAt()) {
          line = regexMatcher.replaceAll(replaceString); 

..so on

This logic works as long as the search string is in the beginning of each line in the file. otherwise the pattern matching does not occur. Can anyone please suggest a solution?

for eg. My search String is "This" and Replace string is "That"
Input file contains: This is not This funny
Output: That is not That funny

But when
Input file contains: 007 This is not This funny
Output: 007 This is not This funny

Answer 1

Shouldn't it be...?

patternMatcher = Pattern.compile(searchString);
while ((line = readLine()) != null) {
    Matcher regexMatcher = patternMatcher.matcher(line);
       while (regexMatcher.find()) {
          line = regexMatcher.replaceAll(replaceString); 

Take into account that the quatifier may affect the results, perhapaps the search string should be "(this)+" or "(this)+?".

Answer 2

If you're searching for a constant string and not for a pattern, there's a number of reasons why you shouldn't use regex:

• The user might type in some character that has a special meaning in regex grammar.
• Regular expressions are slow compared to substring searching.
• You don't want to allow the user more features (using regex matching) than you intend to.

Use String.indexOf and/or String.replace instead.

while ((line = readLine()) != null)
    if (line.indexOf(searchString) != -1 )
        line.replace(searchString, replaceString);

Answer 3

I'm not familiar with Java, but as per the docs, lookingAt looks at the beginning of the string. I would just skip looking for the match and blindly run replaceAll regardless of whether there is a match; it will replace nothing if there is no match.

If for some reason you need to look for a match before attempting to replace (which is wasteful), the correct function is find . See http://docs.oracle.com/javase/1.4.2/docs/api/java/util/regex/Matcher.html

Answer 4

如果内存不是问题，则可以将整个文件读取为String，并在String API中使用public String replaceAll(String regex, String replacement) 。