How to replace tokens in java using regex?

Question

I am having a string template containing $variables which needs to be replaced.

String Template: "hi my name is $name.\nI am $age old. I am $sex"

The solution which i tried verifying does not work in the java program. http://regexr.com/3dtq1

Further, I referred to https://www.regex101.com/ where i could not check if the pattern works for java. But, while going through one of the tutorials I found that "$ Matches end of line". what's the best way to replace the tokens in the template with the variables?

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

public class PatternCompiler {
    static String text = "hi my name is $name.\nI am $age old. I am $sex";
    static Map<String,String> replacements = new HashMap<String,String>();
    static Pattern pattern = Pattern.compile("\\$\\w+");
    static Matcher matcher = pattern.matcher(text);

    public static void main(String[] args) {

        replacements.put("name", "kumar");
        replacements.put("age", "26");
        replacements.put("sex", "male");

        StringBuffer buffer = new StringBuffer();

        while (matcher.find()) {
            String replacement = replacements.get(matcher.group(1));
            if (replacement != null) {
                // matcher.appendReplacement(buffer, replacement);
                // see comment 
                matcher.appendReplacement(buffer, "");
                buffer.append(replacement);
            }
        }
        matcher.appendTail(buffer);
        System.out.println(buffer.toString());


    }

}

That should work fine. You've escaped the $ appropriately (\), so it wont match end of line. Whats the error? — Drgabble
– Drgabble, Commented Aug 1, 2016 at 15:02

Krzysztof Krasoń · Accepted Answer · 2016-08-01 15:15:58Z

3

You are using matcher.group(1) but you didn't define any group in the regexp (( )), so you can use only group() for the whole matched string, which is what you want.

Replace line:

String replacement = replacements.get(matcher.group(1));

With:

String replacement = replacements.get(matcher.group().substring(1));

Notice the substring, your map contains only words, but matcher will match also $, so you need to search in map for "$age".substring(1)" but do replacement on the whole $age.

edited Aug 1, 2016 at 15:15

answered Aug 1, 2016 at 15:05

Krzysztof Krasoń

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5 Comments

Drgabble Over a year ago

not quite right - he doesn't want the whole string, just the word after the dollar

Krzysztof Krasoń Over a year ago

OK, but he needs to replace the text in the string also, so he needs actually both $age and age. He can get either of those by adding or removing the $.

wandermonk Over a year ago

I tied using the static Pattern pattern = Pattern.compile("\\$\\w+"); but it is still not working for me.

Drgabble Over a year ago

@krzyk ah good point. It does still require brackets to capture though "(\\$\\w+)"?

Krzysztof Krasoń Over a year ago

@dataEnthusiast Corrected case to take into account your map content, try again.

FriedSaucePots · Accepted Answer · 2016-08-01 15:05:30Z

1

You can try replacing the pattern string with

\\$(\\w+)

and the variable replacement works. Your current pattern only has group 0 (the entire pattern) but not group 1. Adding the parenthesis makes the first group the variable name and the replacement will replace the dollar sign and the variable name.

answered Aug 1, 2016 at 15:05

FriedSaucePots

1,35211 silver badges16 bronze badges

Comments

Joop Eggen · Accepted Answer · 2016-08-01 15:05:01Z

0

Your code has just minor glitches.

    static Map<String,String> replacements = new HashMap<>();
    static Pattern pattern = Pattern.compile("\\$\\w+\\b"); // \b not really needed

            // As no braces (...) there is no group(1)
            String replacement = replacements.get(matcher.group());

answered Aug 1, 2016 at 15:05

Joop Eggen

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Comments

Drgabble · Accepted Answer · 2016-08-01 15:39:24Z

Your not using the right thing as your key. Change to group(), and change map to '$name' etc:

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

public class HelloWorld {
    static String text = "hi my name is $name.\nI am $age old. I am $sex";
    static Map<String,String> replacements = new HashMap<String,String>();
    static Pattern pattern = Pattern.compile("\\$\\w+");
    static Matcher matcher = pattern.matcher(text);

    public static void main(String[] args) {

        replacements.put("$name", "kumar");
        replacements.put("$age", "26");
        replacements.put("$sex", "male");

        StringBuffer buffer = new StringBuffer();

        while (matcher.find()) {
            String replacement = replacements.get(matcher.group());
            System.out.println(replacement);
            if (replacement != null) {
                // matcher.appendReplacement(buffer, replacement);
                // see comment 
                matcher.appendReplacement(buffer, "");
                buffer.append(replacement);
            }
        }
        matcher.appendTail(buffer);
        System.out.println(buffer.toString());


    }

}

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