Apache Commons

Apache Commons

Apache Commons is a popular set of reusable Java components developed by the Apache Software Foundation. Its goal is to provide well-tested, reusable code to simplify common programming tasks, so you don’t have to reinvent the wheel. It is widely used in enterprise and open-source projects.

Here’s a structured overview:

1. Core Libraries in Apache Commons

Apache Commons is divided into multiple sub-projects (modules), each focusing on a specific area. Some of the most commonly used are:

ModulePurpose
Commons LangUtilities for java.lang classes (String manipulation, ObjectUtils, ArrayUtils, NumberUtils)
Commons IOUtilities for I/O operations (reading/writing files, file filters, file comparison)
Commons CollectionsEnhancements to Java collections (e.g., Bag, MultiMap, BidiMap)
Commons MathMathematical and statistical functions
Commons CodecEncoding and decoding utilities (Base64, Hex, URL encoding)
Commons BeanUtilsReflection and property manipulation for JavaBeans
Commons ConfigurationHandling configuration files (properties, XML, INI)
Commons ValidatorValidation framework for strings, emails, dates, etc.

2. Adding Apache Commons to a Project

If you’re using Maven, you can add a dependency like this:

<!-- Example: Apache Commons Lang -->
<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.13.0</version>
</dependency>

For Gradle:

implementation 'org.apache.commons:commons-lang3:3.13.0'

3. Example Usage

Commons Lang (StringUtils)

import org.apache.commons.lang3.StringUtils;

public class Example {
    public static void main(String[] args) {
        String str = " Hello World ";
        System.out.println(StringUtils.isBlank(str));  // false
        System.out.println(StringUtils.trim(str));     // "Hello World"
        System.out.println(StringUtils.reverse(str));  // " dlroW olleH "
    }
}

Commons IO (FileUtils)

import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;

public class ExampleIO {
    public static void main(String[] args) throws IOException {
        File file = new File("example.txt");
        // Write string to file
        FileUtils.writeStringToFile(file, "Hello Apache Commons!", "UTF-8");
        // Read string from file
        String content = FileUtils.readFileToString(file, "UTF-8");
        System.out.println(content);
    }
}

4. Why Use Apache Commons?

  1. Reduces boilerplate code – simplifies operations on Strings, collections, files, etc.
  2. Well-tested and maintained – reduces bugs compared to writing your own utility methods.
  3. Cross-project consistency – widely adopted across Java projects.

1. Commons Lang (org.apache.commons.lang3)

String Utilities – StringUtils

import org.apache.commons.lang3.StringUtils;

String str = " Hello World ";

// Check if string is empty or blank
StringUtils.isEmpty(str);  // false
StringUtils.isBlank(str);  // false

// Trim, reverse, capitalize
StringUtils.trim(str);     // "Hello World"
StringUtils.reverse(str);  // " dlroW olleH "
StringUtils.capitalize("hello"); // "Hello"

// Check prefix/suffix ignoring case
StringUtils.startsWithIgnoreCase("Hello", "he"); // true

Object Utilities – ObjectUtils

import org.apache.commons.lang3.ObjectUtils;

Object a = null;
Object b = ObjectUtils.defaultIfNull(a, "Default"); // "Default"

Array Utilities – ArrayUtils

import org.apache.commons.lang3.ArrayUtils;

int[] numbers = {1, 2, 3};
ArrayUtils.add(numbers, 4);   // [1, 2, 3, 4]
ArrayUtils.contains(numbers, 2); // true

2. Commons IO (org.apache.commons.io)

File Utilities – FileUtils

import org.apache.commons.io.FileUtils;
import java.io.File;
import java.io.IOException;

File file = new File("example.txt");

// Write to file
FileUtils.writeStringToFile(file, "Hello World!", "UTF-8");

// Read from file
String content = FileUtils.readFileToString(file, "UTF-8");

// Copy files
FileUtils.copyFile(new File("source.txt"), new File("dest.txt"));

Filename and File Filters

import org.apache.commons.io.FilenameUtils;

String name = "example.txt";
FilenameUtils.getExtension(name); // "txt"
FilenameUtils.getBaseName(name);  // "example"

3. Commons Collections (org.apache.commons.collections4)

import org.apache.commons.collections4.Bag;
import org.apache.commons.collections4.bag.HashBag;

Bag<String> bag = new HashBag<>();
bag.add("apple", 2); // adds 2 apples
bag.add("orange");
bag.getCount("apple"); // 2

4. Commons Codec (org.apache.commons.codec)

import org.apache.commons.codec.binary.Base64;

String original = "Hello";
String encoded = Base64.encodeBase64String(original.getBytes());
String decoded = new String(Base64.decodeBase64(encoded));

5. Commons Math (org.apache.commons.math3)

import org.apache.commons.math3.stat.descriptive.DescriptiveStatistics;

DescriptiveStatistics stats = new DescriptiveStatistics();
stats.addValue(10);
stats.addValue(20);
stats.addValue(30);

stats.getMean();  // 20.0
stats.getStandardDeviation(); // ~8.16

6. Commons BeanUtils (org.apache.commons.beanutils)

import org.apache.commons.beanutils.BeanUtils;

class Person {
    private String name;
    public String getName() { return name; }
    public void setName(String name) { this.name = name; }
}

Person p = new Person();
BeanUtils.setProperty(p, "name", "Alice");
String name = BeanUtils.getProperty(p, "name"); // "Alice"

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