11 February 2020

Extract Numbers From String Using Java Regular Expressions

development

The following are examples which show how to extract numbers from a string using regular expressions in Java.

Being able to parse strings and extract information from it is a key skill that every tester should have. This is particularly useful when testing APIs and you need to parse a JSON or XML response.

The following Java Regular Expression examples focus on extracting numbers or digits from a String.

Extract All Numbers from a String

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

public class RegexExamples {
    public static void main(String[]args) {
        Pattern p = Pattern.compile("\\d+");
        Matcher m = p.matcher("string1234more567string890");
        while(m.find()) {
            System.out.println(m.group());
        }
    }
}

Output:

1234
567
890

Extract nth Digit from a String

If you want to extract only certain numbers from a string you can provide an index to the group() function.

For example, if we wanted to only extract the second set of digits from the string string1234more567string890, i.e. 567 then we can use:

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

public class RegexExamples {
    private static final Pattern p = Pattern.compile("[^\\d]*[\\d]+[^\\d]+([\\d]+)");
    public static void main(String[] args) {
        // create matcher for pattern p and given string
        Matcher m = p.matcher("string1234more567string890");

        // if an occurrence if a pattern was found in a given string...
        if (m.find()) {
            System.out.println(m.group(1)); // second matched digits
        }
    }
}

Output:

Explanation of the Pattern [^\d]*[\d]+[^\d]+([\d]+)

ignore any non-digit
ignore any digit (first number)
again ignore any non-digit
capture the second number

Extract Number from a Tag Attribute

When dealing with XML or HTML tags, sometimes there is a need to extract a value from an attribute. For example, consider the following tag

<result name="response" numFound="9999" start="0">

To extract number 9999 we can use the following code:

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

public class RegexExamples {
    public static void main(String[]args) {
        Pattern pattern = Pattern.compile("numFound=\"([0-9]+)\"");
        Matcher matcher = pattern.matcher("");

        if (matcher.find()) {
            System.out.println(matcher.group(1));
        }
    }
}

Output:

Extract a String Containing digits and Characters

You can use Java regular expressions to extract a part of a String which contains digits and characters. Suppose we have this string Sample_data = YOUR SET ADDRESS IS 6B1BC0 TEXT and we want to extract 6B1BC0 which is 6 characters long, we can use:

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

public class RegexExamples {
    public static void main (String[] args) {
        Pattern p = Pattern.compile("YOUR SET ADDRESS IS\\s+([A-Z0-9]{6})");
        Matcher n = p.matcher("YOUR SET ADDRESS IS 6B1BC0 TEXT");
        if (n.find()) {
            System.out.println(n.group(1)); // Prints 123456
        }
    }
}

Output:

6B1BC0

Extract Key-Value Pairs With Regular Expressions

Let’s suppose we have a string of this format bookname=testing&bookid=123456&bookprice=123.45 and we want to extract the key-value pair bookid=123456 we would use:

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

public class RegexExamples {
    public static void main(String[] args) {
        String s = "bookname=cooking&bookid=123456&bookprice=123.45";
        Pattern p = Pattern.compile("(?<=bookid=)\\d+");
        Matcher m = p.matcher(s);
        if (m.find()) {
            System.out.println(m.group());
        }
    }
}

Output:

11 February 2020