String Handling with Apache Commons’ StringUtils Class in Java

The Apache Commons Lang library is a popular third-party library for working with Strings in Java, and the StringUtils class is a key part of this library. StringUtils is a utility class that provides a wide range of String manipulation methods that are not available in the standard Java String class.

Key Features of The StringUtils Class

• Null-safe methods: Many of the methods in the StringUtils class are designed to handle null Strings gracefully, rather than throwing NullPointerExceptions. For example, the isBlank() method checks whether a String is null or contains only whitespace characters.
• Methods for manipulating Strings: The StringUtils class provides a range of methods for manipulating Strings, such as trim() to remove leading and trailing whitespace, and substringBefore() and substringAfter() to extract substrings.
• Methods for comparing Strings: The StringUtils class provides methods for comparing Strings, such as equals() and equalsIgnoreCase(), that handle null Strings and avoid NullPointerExceptions.
• Methods for formatting Strings: The StringUtils class provides methods for formatting Strings, such as join() to join an array of Strings into a single String with a separator.
• Methods for handling cases: The StringUtils class provides methods for changing the case of Strings, such as capitalize() to capitalize the first letter of a String, and swapCase() to swap the case of the characters in a String.
• Methods for searching Strings: The StringUtils class provides methods for searching Strings, such as contains() to check whether a String contains a given substring, and indexOf() to find the index of a given substring.
• Methods for manipulating whitespace: The StringUtils class provides methods for manipulating whitespace in Strings, such as normalizeSpace() to convert multiple whitespace characters to a single space, and replaceEach() to replace multiple whitespace characters with a single character.
• Methods for working with characters: The StringUtils class provides methods for working with individual characters in Strings, such as countMatches() to count the number of occurrences of a given character or substring, and remove() to remove a specific character or substring from a String.
• Methods for formatting numbers: The StringUtils class provides methods for formatting numbers as Strings, such as leftPad() and rightPad() to pad a number with leading or trailing zeros or spaces.
• Methods for handling line breaks: The StringUtils class provides methods for handling line breaks in Strings, such as replaceEach() to replace multiple lines breaks with a single line break, and split() to split a String into an array of Strings based on line breaks.

Getting Started with Apache Commons for Maven and Gradle involves the following steps:

For Maven:

Add the Apache Commons Lang dependency to your pom.xml file

XML

<dependency>
    <groupId>org.apache.commons</groupId>
    <artifactId>commons-lang3</artifactId>
    <version>3.12.0</version>
</dependency>

Run a Maven build to download the dependency and add it to your project’s classpath. Import the StringUtils class in your Java code.

import org.apache.commons.lang3.StringUtils;

Use the StringUtils class in your Java code, as described in the previous answer.

For Gradle:

Add the Apache Commons Lang dependency to your build.gradle file:

dependencies {
   implementation 'org.apache.commons:commons-lang3:3.12.0'
}

Run a Gradle build to download the dependency and add it to your project’s classpath. Import the StringUtils class in your Java code:

import org.apache.commons.lang3.StringUtils;

Use the StringUtils class in your Java code, as described in the previous answer.

StringUtils Class Available utility Methods

A list of some of the methods available in the StringUtils class of Apache Commons Lang, along with a brief explanation of what each method does:

1. isBlank(String str): This method checks if a String is null, empty, or contains only whitespace characters. It returns true if the String is blank, and false otherwise.
2. join(Object[] array, String separator): This method joins an array of Objects into a single String, with each element separated by the specified separator. It returns the joined String.
3. capitalize(String str): This method capitalizes the first letter of a String and returns the modified String.
4. remove(String str, char remove): This method removes all occurrences of a specified character from a String and returns the modified String.
5. reverse(String str): This method reverses the order of characters in a String and returns the reversed String.
6. substringBefore(String str, String separator): This method returns the substring of a String before the first occurrence of a specified separator. If the separator is not found in the String, the entire String is returned.
7. substringAfter(String str, String separator): This method returns the substring of a String after the first occurrence of a specified separator. If the separator is not found in the String, an empty String is returned.
8. substringBetween(String str, String open, String close): This method returns the substring of a String between two specified markers. If either marker is not found in the String, null is returned.
9. countMatches(String str, String sub): This method counts the number of occurrences of a specified substring within a String and returns the count as an integer.
10. isNumeric(String str): This method checks if a String contains only numeric characters (0-9) and optionally a minus sign at the beginning. It returns true if the String is numeric, and false otherwise.

Examples

Below Are the Programs that demonstrate StringUtility class Methods.

Example 1:

Java

import org.apache.commons.lang3.StringUtils;

public class StringUtilsExample {

    public static void main(String[] args) {

        String str = "   hello world   ";

        // isEmpty() example
        boolean empty = StringUtils.isEmpty(str);
        System.out.println("Is the string empty? " + empty);

        // isBlank() example
        boolean blank = StringUtils.isBlank(str);
        System.out.println("Is the string blank? " + blank);

        // trim() example
        String trimmed = StringUtils.trim(str);
        System.out.println("The trimmed string is: " + trimmed);

        // substring() example
        String substring = StringUtils.substring(str, 2, 7);
        System.out.println("The substring is: " + substring);

        // replace() example
        String replaced = StringUtils.replace(str, "world", "Java");
        System.out.println("The replaced string is: " + replaced);

        // split() example
        String[] words = StringUtils.split(str);
        System.out.println("The words in the string are:");
        for (String word : words) {
            System.out.println(word);
        }

        // join() example
        String[] fruits = {"apple", "banana", "orange"};
        String joined = StringUtils.join(fruits, ", ");
        System.out.println("The joined string is: " + joined);

        // capitalize() example
        String capitalized = StringUtils.capitalize(str);
        System.out.println("The capitalized string is: " + capitalized);

        // equalsIgnoreCase() example
        boolean equal = StringUtils.equalsIgnoreCase(str, "   Hello World   ");
        System.out.println("Are the strings equal? " + equal);
    }
}

Output:

Is the string empty? false
Is the string blank? false
The trimmed string is: hello world
The substring is: llo w
The replaced string is:    hello Java   
The words in the string are:
hello
world
The joined string is: apple, banana, orange
The capitalized string is:    Hello world   
Are the strings equal? true

Note: You’ll need to have the Apache Commons Lang library added to your project’s classpath in order for this program to compile and run successfully. 

Example 2:

Java

import org.apache.commons.lang3.StringUtils;

public class StringUtilsExample {

    public static void main(String[] args) {

        String str1 = "Hello";
        String str2 = "World";

        // concatenate two strings
        String result1 = StringUtils.join(new String[]{str1, str2}, " ");
        System.out.println("Result 1: " + result1);

        // repeat a string
        String result2 = StringUtils.repeat(str1, 3);
        System.out.println("Result 2: " + result2);

        // capitalize first letter
        String result3 = StringUtils.capitalize(str1);
        System.out.println("Result 3: " + result3);

        // swap case
        String result4 = StringUtils.swapCase(str2);
        System.out.println("Result 4: " + result4);

        // count matches
        int result5 = StringUtils.countMatches(result1, "l");
        System.out.println("Result 5: " + result5);
    }
}

Output:

Result 1: Hello World
Result 2: HelloHelloHello
Result 3: Hello
Result 4: wORLD
Result 5: 3

Explanation:

• isNullOrEmpty(String str) – This method takes a string as input and checks if the string is null or empty. If the string is null or empty, it returns true, otherwise, it returns false.
• reverse(String str) – This method takes a string as input and reverses the string. It uses a StringBuilder to append each character of the string in reverse order. It then returns the reversed string.
• countOccurrences(String str, String sub) – This method takes two strings as input – a string and a substring. It then counts the number of occurrences of the substring in the string and returns the count.
• All the methods are static, so they can be accessed without creating an object of the StringUtils class. The methods are useful in different scenarios such as checking if a string is empty, reversing a string, or counting the number of occurrences of a substring in a string.

Note: You’ll need to have the Apache Commons Lang library added to your project’s classpath in order for this program to compile and run successfully.

Some Additional Insights on StringUtils class in Java

• The StringUtils class provides a number of convenient methods for working with Strings, which can save you time and simplify your code. For example, instead of writing your own method to check if a String is empty or null, you can use the isEmpty() method from the StringUtils class.
• Many of the methods in the StringUtils class have equivalent methods in the standard String class in Java. However, the StringUtils versions often have additional functionality, such as handling null inputs gracefully or ignoring cases when comparing strings.
• The StringUtils class is part of the Apache Commons Lang library, which provides many other useful utility classes for working with Java code. If you find yourself using the StringUtils class frequently, you might want to explore some of the other classes in this library to see if they can help you simplify your code further.
• When using the StringUtils class, be aware that some of the methods can throw a NullPointerException if you pass in a null value. To avoid this, you can either check for null inputs explicitly before calling a StringUtils method or use the StringUtils.defaultString() method to convert null inputs to empty strings.
• When using the split() method in the StringUtils class, be aware that it uses whitespace as the default delimiter if no delimiter is specified. If you want to split on a different character or sequence of characters, you’ll need to pass that in as a parameter to the split() method.

Overall, the StringUtils class is a powerful and convenient tool for working with Strings in Java. By learning about the different methods it provides and how to use them effectively, you can simplify your code and save time in your Java programming projects.