find and replace characters using regexp java string

Question

I want to replace special characters between the following String when only when they are between two words, BEGIN and END . xxx to CCC and yyy to DDD, using Java regular expression or some way ? can you help

Raw string = "John Doe xxx Amazing man BEGIN reference xxx yes yyy indeed this is true xxx 
no yyy END , so this xxx does not change" 

converted String = "John Doe xxx Amazing man BEGIN reference CCC yes DDD indeed this is true 
CCC no DDD END, so this xxx does not change" 

Answer 1

You need to define your pattern and matcher:

Pattern MY_PATTERN = Pattern.compile("BEGIN" + "([ ]*+[0-9A-Za-z]++[ ]*+)*" + "xxx" + "([ ]*+[0-9A-Za-z]++[ ]*+)*" + "END");
Matcher m = MY_PATTERN.matcher(rawString);

Then you will call the find method on the matcher and every time it finds what you wanted will replace it with what you needed:

 while (m.find()) {
        rawString = rawString.replaceFirst(m.group(0),m.group(0).replaceAll("xxx","CCC"));
    }

Answer 2

Even though your sample data displays "xxx" before "yyy" , there's no specification if "xxx" is before "yyy" or vice versa. You just state, "special characters between the following String when only when they are between two words, BEGIN and END" .

I see having a Map<String, String> where the keys are your "special" strings and the values are the strings that'll replace the "special" strings.

Iterate through this map and provide the keys to this:

String.format("BEGIN.*?(%s).*?END", kvp.getKey())

In this example, it'll produce two regex patterns:

"BEGIN.*?(xxx).*?END"
"BEGIN.*?(yyy).*?END"

This will capture your "special" strings into capture group 1, which you'll provide to String.replace() like so:

raw = raw.replace(matcher.group(), matcher.group().replace(matcher.group(1), kvp.getValue()));

matcher.group() is the entire matching string BEGIN ... END and matcher.group(1) will either be xxx or yyy

Put this all together and you have:

public static void main(String[] args) throws Exception {
    Map<String, String> replacerMap = new HashMap() {{
        put("xxx", "CCC");
        put("yyy", "DDD");
    }};

    String raw = "John Doe xxx Amazing man BEGIN reference xxx yes yyy indeed this is true xxx no yyy END , so this xxx does not change";
    System.out.println("Before: ");
    System.out.println(raw);
    System.out.println();

    for (Map.Entry<String, String> kvp : replacerMap.entrySet()) {
        Matcher matcher = Pattern.compile(String.format("BEGIN.*?(%s).*?END", kvp.getKey())).matcher(raw);
        if (matcher.find()) {
            raw = raw.replace(matcher.group(), matcher.group().replace(matcher.group(1), kvp.getValue()));
        }
    }

    System.out.println("After: ");
    System.out.println(raw);
}

Results:

Before: 
John Doe xxx Amazing man BEGIN reference xxx yes yyy indeed this is true xxx no yyy END , so this xxx does not change

After: 
John Doe xxx Amazing man BEGIN reference CCC yes DDD indeed this is true CCC no DDD END , so this xxx does not change