Refactoring 019 - Reify Email Addresses

Sayit once and only once

Maximiliano Contieri

Dec 05, 2024

TL;DR: Avoid duplicate email validations.

Problems Addressed

Repeated email validation logic in multiple places.
Risk of inconsistent validation rules.
Bijection violation
Primitive Obsession
Premature Optimization

Related Code Smells

Code Smell 46 - Repeated Code

Code Smell 122 - Primitive Obsession

Code Smell 66 - Shotgun Surgery

Code Smell 177 - Missing Small Objects

Code Smell 20 - Premature Optimization

Steps

Identify where email validation logic is duplicated.
Create an Email Address class to encapsulate validation rules.
Refactor code to use the Email Address class instead of raw strings.

Sample Code

Before

public class Person {
    private String emailAddress;
    // Primitive Obsession

    public void setEmailAddress(String emailAddress) {
        // Duplicated code
        if (!emailAddress.matches(
            "^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) {
            throw new IllegalArgumentException(
                "Invalid email address format");
        }
        this.emailAddress = emailAddress;
    }
}

public class JobApplication {
    private String applicantEmailAddress;

    public void setApplicantEmailAddress(String emailAddress) {
        // Duplicated code
        if (!emailAddress.matches(
            "^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) {
            throw new IllegalArgumentException(
                "Invalid email address format");
        }
        this.applicantEmailAddress = emailAddress;
    }
}

After

public class EmailAddress {
    // 2. Create an `EmailAddress` class to encapsulate validation rules.
    private final String value;

    public EmailAddress(String value) {
        // The rules are in a single place
        // And all objects are created valid
        if (!value.matches("^[\\w.%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$")) {
            throw new IllegalArgumentException(
                "Invalid email address format");
        }
        this.value = value;
    }
}

public class Person {
    private final EmailAddress emailAddress;

    public Person(EmailAddress emailAddress) {
        // 1. Identify where email validation logic is duplicated.
        // 3. Refactor code to use the `Email Address`
        // class instead of raw strings.
        // No validation is required
        this.emailAddress = emailAddress;
    } 
}

public class JobApplication {
    private EmailAddress applicantEmailAddress;

    public JobApplication(EmailAddress applicantEmailAddress) {
        this.applicantEmailAddress = applicantEmailAddress;
    }
}

Type

[X] Semi-Automatic

Safety

This refactoring is safe if you replace all occurrences of raw email strings with the 'EmailAddress' class and ensure all tests pass.

Why is the Code Better?

You make email validation consistent across your application.

Since validation rules are centralized in one place, the code becomes easier to maintain.

You also reduce the risk of bugs caused by inconsistent logic.

In the real world, Email Addresses are small objects that exist and are not strings.

The refactored code is closer to the real world MAPPER.

Notice that bijection names are essential. It would help to create an EmailAddress, not an Email, since the Email should map to the actual message.

Don't let Premature Optimizators tell you this solution has a performance penalty.

They never do actual benchmarks with real world data.

Refactor with AI

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Related Refactorings

Refactoring 007 - Extract Class

Refactoring 012 - Reify Associative Arrays

Refactoring 002 - Extract Method

Credits

Image by Gerd Altmann on Pixabay

This article is part of the Refactoring Series.

How to Improve Your Code With Easy Refactorings

Clean Code Cookbook

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