🔧 Top 25 Utility Functions Every Java Project Needs - Part 1

 🧾 Introduction

Whether you’re working on a small utility tool or a massive enterprise application, certain utility functions are always helpful. They save time, reduce repetition, and improve code quality.

In this two-part guide, we’ll cover 25 essential utility functions — written using modern Java features. In Part 1, we'll explore the first 10.

1. isNullOrBlank(String input)

Checks whether a string is null or blank (empty or whitespace only).

✅ Java Implementation:

public static boolean isNullOrBlank(String input) {
    return input == null || input.isBlank();
}

🔄 Usage:

if (isNullOrBlank(user.getName())) {
    throw new IllegalArgumentException("Name cannot be blank");
}

---

2. capitalize(String input)

Converts the first letter to uppercase and leaves the rest unchanged.

✅ Java Implementation:

public static String capitalize(String input) {
    if (isNullOrBlank(input)) return input;
    return input.substring(0, 1).toUpperCase() + input.substring(1);
}

🔄 Usage:

String title = capitalize("java"); // Output: Java

---

3. safeToString(Object obj)

Safely converts an object to a string, returning an empty string if null.

✅Java Implementation:

public static String safeToString(Object obj) {
    return Optional.ofNullable(obj).map(Object::toString).orElse("");
}

🔄 Usage:

System.out.println("User: " + safeToString(user.getUsername()));

---

4. generateUUID()

Generates a universally unique identifier.

✅ Java Implementation:

public static String generateUUID() {
    return UUID.randomUUID().toString();
}

🔄 Usage:

String transactionId = generateUUID();

---

5. isNumeric(String str)

Checks whether a string contains only digits.

✅ Java Implementation:

public static boolean isNumeric(String str) {
    return Optional.ofNullable(str)
        .map(s -> s.matches("\\d+"))
        .orElse(false);
}

🔄 Usage:

if (isNumeric(ageInput)) {
    int age = Integer.parseInt(ageInput);
}

---

6. removeDuplicates(List<T> list)

Removes duplicate entries from a list while preserving order.

✅ Java Implementation:

public static <T> List<T> removeDuplicates(List<T> list) {
    return list == null ? List.of() : new ArrayList<>(new LinkedHashSet<>(list));
}

🔄 Usage:

List<String> tags = removeDuplicates(List.of("java", "spring", "java"));

---

7. formatDate(LocalDateTime dt, String pattern)

Formats a date using the specified pattern.

✅ Java Implementation:

public static String formatDate(LocalDateTime dt, String pattern) {
    return dt.format(DateTimeFormatter.ofPattern(pattern));
}

🔄 Usage:

String formatted = formatDate(LocalDateTime.now(), "dd-MM-yyyy HH:mm");

---

8. parseDate(String dateStr, String pattern)

Parses a string into a LocalDateTime object.

✅ Java Implementation:

public static LocalDateTime parseDate(String dateStr, String pattern) {
    return LocalDateTime.parse(dateStr, DateTimeFormatter.ofPattern(pattern));
}

🔄 Usage:

LocalDateTime dt = parseDate("11-04-2025 10:30", "dd-MM-yyyy HH:mm");

---

9. isValidEmail(String email)

Checks whether the input is a valid email address.

✅Java Implementation:

public static boolean isValidEmail(String email) {
    return Optional.ofNullable(email)
        .map(e -> e.matches("^[\\w._%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$"))
        .orElse(false);
}

🔄 Usage:

if (!isValidEmail(user.getEmail())) {
    throw new IllegalArgumentException("Email is invalid.");
}

---

10. retry(Runnable task, int attempts)

Retries a failing task a fixed number of times.

✅ Java Implementation:

public static void retry(Runnable task, int attempts) {
    Objects.requireNonNull(task);
    for (int i = 0; i < attempts; i++) {
        try {
            task.run();
            return;
        } catch (Exception ex) {
            if (i == attempts - 1) throw ex;
        }
    }
}

🔄 Usage:

retry(() -> sendEmail(), 3);

✅ Especially useful for network calls or flaky I/O operations.

---

✅ Final Thoughts for Part 1

These 10 utility functions can help you simplify common tasks such as formatting, validation, collection handling, and error retry logic.

They are:

1. isNullOrBlank
2. capitalize
3. safeToString
4. generateUUID
5. isNumeric
6. removeDuplicates
7. formatDate
8. parseDate
9. isValidEmail
10. retry

Here is the complete code in a single Java class for your reference:

package com.example.utils;

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;
import java.util.*;

public class JavaUtilsPart1 {

    public static boolean isNullOrBlank(String input) {
        return input == null || input.isBlank();
    }

    public static String capitalize(String input) {
        if (isNullOrBlank(input)) return input;
        return input.substring(0, 1).toUpperCase() + input.substring(1);
    }

    public static String safeToString(Object obj) {
        return Optional.ofNullable(obj).map(Object::toString).orElse("");
    }

    public static String generateUUID() {
        return UUID.randomUUID().toString();
    }

    public static boolean isNumeric(String str) {
        return Optional.ofNullable(str)
                .map(s -> s.matches("\\d+"))
                .orElse(false);
    }

    public static <T> List<T> removeDuplicates(List<T> list) {
        return list == null ? List.of() : new ArrayList<>(new LinkedHashSet<>(list));
    }

    public static String formatDate(LocalDateTime dt, String pattern) {
        return dt.format(DateTimeFormatter.ofPattern(pattern));
    }

    public static LocalDateTime parseDate(String dateStr, String pattern) {
        return LocalDateTime.parse(dateStr, DateTimeFormatter.ofPattern(pattern));
    }

    public static boolean isValidEmail(String email) {
        return Optional.ofNullable(email)
                .map(e -> e.matches("^[\\w._%+-]+@[\\w.-]+\\.[a-zA-Z]{2,}$"))
                .orElse(false);
    }

    public static void retry(Runnable task, int attempts) {
        Objects.requireNonNull(task);
        for (int i = 0; i < attempts; i++) {
            try {
                task.run();
                return;
            } catch (Exception ex) {
                if (i == attempts - 1) throw ex;
            }
        }
    }
}

Each function is stateless, reusable, and designed for readability and testability.

📌 Next Up:
In Part 2, we’ll cover 15 more utility methods, including file utilities, advanced collection helpers, string transformation tools, optional-safe handling, and more.