Apache Commons

Apache Commons provides a comprehensive set of utility classes for common programming tasks.

import org.apache.commons.lang3.StringUtils;
import org.apache.commons.lang3.RandomStringUtils;
import org.apache.commons.collections4.Bag;
import org.apache.commons.collections4.bag.HashBag;

public class CommonsDemo {
    
    public static void validateStrings() {
        String empty = "";
        String nullStr = null;
        String whitespace = " ";
        
        System.out.println("Empty check: " + StringUtils.isEmpty(empty));
        System.out.println("Null check: " + StringUtils.isEmpty(nullStr));
        System.out.println("Whitespace check: " + StringUtils.isEmpty(whitespace));
        
        String numeric = "123";
        String mixed = "12a3";
        System.out.println("Numeric validation: " + StringUtils.isNumeric(numeric));
        System.out.println("Mixed validation: " + StringUtils.isNumeric(mixed));
    }
    
    public static void generateRandomData() {
        System.out.println("Random numbers: " + RandomStringUtils.randomNumeric(8));
        System.out.println("Random letters: " + RandomStringUtils.randomAlphabetic(8));
    }
    
    public static void demonstrateBag() {
        Bag<String> colorBag = new HashBag<>();
        colorBag.add("red", 3);
        colorBag.add("blue", 2);
        colorBag.add("green");
        
        System.out.println("Red count: " + colorBag.getCount("red"));
        System.out.println("Total items: " + colorBag.size());
    }
}

Google Guava

Guava offers powerful collection utilities and functional programming features.

import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.collect.*;

public class GuavaExamples {
    
    public static void immutableCollections() {
        ImmutableList<String> colors = ImmutableList.of("red", "green", "blue");
        ImmutableMap<Integer, String> numberMap = ImmutableMap.of(1, "one", 2, "two");
        
        System.out.println("Immutable list: " + colors);
        System.out.println("Immutable map: " + numberMap);
    }
    
    public static void multiValueMap() {
        Multimap<String, String> phoneBook = ArrayListMultimap.create();
        phoneBook.put("Alice", "123-4567");
        phoneBook.put("Alice", "987-6543");
        phoneBook.put("Bob", "555-1234");
        
        System.out.println("Alice's phones: " + phoneBook.get("Alice"));
    }
    
    public static void stringOperations() {
        String joined = Joiner.on("; ").join("apple", "banana", "cherry");
        Iterable<String> split = Splitter.on(',').trimResults().split("one, two , three");
        
        System.out.println("Joined: " + joined);
        split.forEach(System.out::println);
    }
}

Joda-Time

Joda-Time provides robust date and time manipulation capabilities.

import org.joda.time.DateTime;
import org.joda.time.format.DateTimeFormat;
import org.joda.time.format.DateTimeFormatter;

public class DateTimeHandling {
    
    public static void dateOperations() {
        DateTime current = new DateTime();
        DateTime future = current.plusMonths(3);
        
        DateTimeFormatter formatter = DateTimeFormat.forPattern("yyyy-MM-dd HH:mm");
        
        System.out.println("Current: " + formatter.print(current));
        System.out.println("Future: " + formatter.print(future));
        System.out.println("Day of week: " + current.dayOfWeek().getAsText());
    }
    
    public static void timeZoneHandling() {
        DateTime utc = new DateTime().withZone(DateTimeZone.UTC);
        DateTime london = new DateTime().withZone(DateTimeZone.forID("Europe/London"));
        
        System.out.println("UTC time: " + utc);
        System.out.println("London time: " + london);
    }
}

Custom Utility Class

A comprehensive utility class coevring common programming needs.

import java.util.*;
import java.util.regex.Pattern;

public final class ApplicationUtils {
    private static final Pattern DIGIT_PATTERN = Pattern.compile("^\\d+$");
    
    public static boolean isBlank(String input) {
        return input == null || input.trim().isEmpty();
    }
    
    public static boolean isNumeric(String input) {
        return !isBlank(input) && DIGIT_PATTERN.matcher(input).matches();
    }
    
    public static String generateRandomCode(int length) {
        String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuilder builder = new StringBuilder();
        
        for (int i = 0; i < length; i++) {
            builder.append(characters.charAt(random.nextInt(characters.length())));
        }
        return builder.toString();
    }
    
    public static <T> boolean hasElements(Collection<T> collection) {
        return collection != null && !collection.isEmpty();
    }
    
    public static String reverseString(String original) {
        if (isBlank(original)) return original;
        return new StringBuilder(original).reverse().toString();
    }
}