JavaRegexTest.java

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class JavaRegexTest {

    public static void main(String []args)
    {
        String textToSearch = "-DARDUINO_BOARD=\"ESP8266_ESP01\" -DDEFINE_NO_2=\"ESP8266_ESP01\" -DALREADY_ESCAPED=\\\"VALUE\\\" -DDEFINE_WITH_WHITESPACE=\"ESP8266 ESP01\"";
        
        Pattern regex = Pattern.compile("-D\\S+=\"\\S+\""); //value contains any char but whitespace 
        Matcher regexMatcher = regex.matcher(textToSearch); 

        String replacedStr = textToSearch;
        System.out.println("----------------------------------------------------------------------------------------------------------------");
        System.out.println("No whitespace replacement");
        System.out.println("----------------------------------------------------------------------------------------------------------------");
        System.out.println("Original text: " + textToSearch);

        while(regexMatcher.find()) {
            System.out.println("Found value:   " + regexMatcher.group(0));
            String newstring = regexMatcher.group(0).replaceAll("\"","\\\\\"");
            System.out.println("Escaped value: " + newstring);
            replacedStr = replacedStr.replace(regexMatcher.group(0), newstring);
        }
        
        System.out.println("New text:      " + replacedStr);
        
        System.out.println("----------------------------------------------------------------------------------------------------------------");
        System.out.println("With whitespace replacement");
        System.out.println("----------------------------------------------------------------------------------------------------------------");
        regex = Pattern.compile("-D\\S+=\".+?\""); //value contains any char including whitespace 
        regexMatcher = regex.matcher(textToSearch); 

        replacedStr = textToSearch;
        System.out.println("Original text: " + textToSearch);

        while(regexMatcher.find()) {
            System.out.println("Found value:   " + regexMatcher.group(0));
            String newstring = regexMatcher.group(0).replaceAll("\"","\\\\\"");
            System.out.println("Escaped value: " + newstring);
            replacedStr = replacedStr.replace(regexMatcher.group(0), newstring);
        }
        
        System.out.println("New text:      " + replacedStr);
    }
}