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Using Generex to Generate Sample Data using Regex

Introduction

• Having test data available is a common requirement in most projects.
• However, it’s always tedious to get realistic test data that is based on production and often we end up creating mock data that suffice the development needs.
• In the previous article, we discussed one approach to generating mock data.
• The goal of this article is to use another approach to generate mock data using regex.

Pre-requisite

• We will need generex dependency that will parse our regex and help us generate data from passed regex.
• Make sure to add it in the pom.xml file

<dependency>
      <groupId>com.github.mifmif</groupId>
      <artifactId>generex</artifactId>
      <version>1.0.2</version>
</dependency>

How does it work?

• We initialize the generex instance by passing our regex to the constructor.
• Once we have generex instance, we can use helper methods such as random(), getFirstMatch(), and getAllMatchedStrings() to generate a record.

Generex generex= new Generex("[REGEX_HERE]");
generex.random(); // generate data

Fields

• username
• age
• zipcode
• phoneNumber
• cardNumber

Generate username

• In order to generate a username field, we will use regex 
  “[a-zA-Z0–9]{18}” 

Generex username = new Generex("[a-zA-Z0-9]{18}");
System.out.println(username.random()); 
// output : 991Pod3a3ZyB87c6ni

• We can also mix names with regex as shown below for usernames to have names+alphanumeric sequence.

List<String> names = List.of("sam", "jam", "tam");
String namesString = names.stream().map(n -> n + "_").collect(Collectors.joining("|"));
Generex username1 = new Generex("("+namesString+")([a-z0-9]{5})");
System.out.println(username1.random()); // jam_b64z5

Generate age

• For age, we are using “(1[89]|[2–9]\\d)” that will generate age between 18–99

Generex age = new Generex("(1[89]|[2-9]\\d)");
System.out.println(age.random()); // 20

Generate ZipCode

• We are using regex for the US zip code.

Generex zipCode = new Generex("\\d{5}(-)\\d{4}");
System.out.println(zipCode.random()); 
//84042-2198

Generate Phone Number

• Using regex for US phone numbers.

Generex phoneNumber = new Generex("([0-9]{3})-([0-9]{3})-([0-9]{4})");
System.out.println(phoneNumber.random());
// 658-101-3783

Generate Card Number

• Generating card numbers considering 16 digit pattern, which is not strictly true for all the cards so maybe we can improve it, but for demo purposes, it’s fine I guess.

Generex cardNumber = new Generex("\\d{4}(-)\\d{4}(-)\\d{4}(-)\\d{4}");
System.out.println(cardNumber.random());
// 4737-4046-5951-7119

Helper method to generate records

• Now that we have regex ready let’s put them all together and create the method generateRecords() that will be called to create mock records.

public static List<String> generateRecord(){
     Generex username = new Generex("[a-zA-Z0-9]{18}");
     List<String> names = List.of("sam", "jam", "tam");
     String namesString = names.stream().map(n -> n + "_").collect(Collectors.joining("|"));
     Generex username1 = new Generex("("+namesString+")([a-z0-9]{5})");
     Generex cardNumber = new Generex("\\d{4}(-)\\d{4}(-)\\d{4}(-)\\d{4}");
     Generex age = new Generex("(1[89]|[2-9]\\d)");
     Generex zipCode = new Generex("\\d{5}(-)\\d{4}");
     Generex phoneNumber = new Generex("([0-9]{3})-([0-9]{3})-([0-9]{4})");
     
     List<String> fields = new ArrayList<>();
     fields.add(username1.random());
     fields.add(age.random());
     fields.add(zipCode.random());
     fields.add(phoneNumber.random());
     fields.add(cardNumber.random());
     return fields;
    }

Generating records in bulk

• Now we can use IntStream from Java 8 streams to generate the range that we need and invoke generateRecord() method which returns a list.
• We then map that list of fields to string with a comma to return as CSV, but we can have any mapper map to any format like JSON and return the result.
• Here we are also printing to the console to verify the output.

    public static void main(String[] args) {
        List<String> records = IntStream.range(1, 100)
                .mapToObj(i -> generateRecord())
                .map(a -> String.join(",", a))
                .peek(System.out::println)
                .toList();
       // sink the records
    }

Output

• Our output seems to generate the records that we wanted for testing.

Conclusion

• In this article, we learned how we can use regex to quickly generate test/mock data.
• generex provides good support to pass regex and helper methods to generate random records.

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