替换正则表达式

Question

I have an input string:

"hello [you], this is [me]"

I have a function which maps a string to a string (hardcoded for the sake of simplicity):

public String map(final String input) {
    if ("you".equals(input)) {
        return "SO";
    } else if ("me".equals(input)) {
        return "Kate";
    }
    ...
}

What is the most convenient way to replace each [(.*)?] occurrence by its respective mapping (given by calling the map function)?

If I am correct, you cannot use String.replaceAll() here, since we don't know the replacement in advance.

Answer 1

First, the expression that you have is greedy. A proper expression to match a token in square brackets is \\[([^\\]]*)\\] (backslashes need to be doubled for Java), because it avoids going past the closing square bracket ^* . I added a capturing group to access the content inside square brackets as group(1) .

Here is a way to do what you need:

Pattern p = Pattern.compile("\\[([^\\]]*)\\]");
Matcher m = p.matcher(input);
StringBuffer bufStr = new StringBuffer();
boolean flag = false;
while ((flag = m.find())) {
    String toReplace = m.group(1);
    m.appendReplacement(bufStr, map(toReplace));
}
m.appendTail(bufStr);
String result = bufStr.toString();

Demo.

^* You can use [.*?] , too, but this reluctant expression may cause backtracking.

Answer 2

You can do something like:

String line = "hello [you], this is [me]";

Pattern p = Pattern.compile("\\[(.*?)\\]");
Matcher m = p.matcher(line);

while (m.find()) {
    // m.group(1) contains the text inside [] 
    // line.replace(m.group(1), yourMap.get(m.group(1)));
    // use StringBuilder to build the new string
}