GH-1 : Refactored pom file and created StringUtils along with basic functions and unit test for them

Author: Abhishek Malvadkar

pom.xml

@@ -2,51 +2,81 @@
 <project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
 	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
 	<modelVersion>4.0.0</modelVersion>
-	<parent>
-		<groupId>org.springframework.boot</groupId>
-		<artifactId>spring-boot-starter-parent</artifactId>
-		<version>3.4.3</version>
-		<relativePath/> <!-- lookup parent from repository -->
-	</parent>
+
 	<groupId>com.amalvadkar</groupId>
 	<artifactId>am-commons-utils</artifactId>
 	<version>0.0.1-SNAPSHOT</version>
+	<packaging>jar</packaging>
 	<name>am-commons-utils</name>
-	<description>Common Utilities</description>
-	<url/>
-	<licenses>
-		<license/>
-	</licenses>
-	<developers>
-		<developer/>
-	</developers>
-	<scm>
-		<connection/>
-		<developerConnection/>
-		<tag/>
-		<url/>
-	</scm>
+	<description>Common Utility Library</description>
+
 	<properties>
+		<!-- Dependency versions management -->
 		<java.version>21</java.version>
+		<junit-jupiter.version>5.10.2</junit-jupiter.version>
+		<assertj-core.version>3.25.3</assertj-core.version>
+
+		<!-- Plugin versions management -->
+		<maven-compiler-plugin.version>3.8.1</maven-compiler-plugin.version>
+		<maven-surefire-plugin.version>3.1.2</maven-surefire-plugin.version>
 	</properties>
+
 	<dependencies>
+		<!-- JUnit 5 API for writing tests -->
+		<dependency>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-api</artifactId>
+			<version>${junit-jupiter.version}</version>
+			<scope>test</scope>
+		</dependency>
+
+		<!-- JUnit 5 Engine for running tests -->
 		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter</artifactId>
+			<groupId>org.junit.jupiter</groupId>
+			<artifactId>junit-jupiter-engine</artifactId>
+			<version>${junit-jupiter.version}</version>
+			<scope>test</scope>
 		</dependency>
 
+		<!-- AssertJ for fluent assertions -->
 		<dependency>
-			<groupId>org.springframework.boot</groupId>
-			<artifactId>spring-boot-starter-test</artifactId>
+			<groupId>org.assertj</groupId>
+			<artifactId>assertj-core</artifactId>
+			<version>${assertj-core.version}</version>
 			<scope>test</scope>
 		</dependency>
+
 	</dependencies>
 
 	<build>
+		<finalName>${project.artifactId}</finalName>
 		<plugins>
+			<!-- Compiler Plugin to Ensure Java 21 Compatibility -->
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-compiler-plugin</artifactId>
+				<version>${maven-compiler-plugin.version}</version>
+				<configuration>
+					<source>${java.version}</source>
+					<target>${java.version}</target>
+				</configuration>
+			</plugin>
+
+			<!-- JAR Plugin for Packaging the Library -->
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-jar-plugin</artifactId>
+				<version>3.2.2</version>
+			</plugin>
+
+			<!-- Surefire Plugin for Running JUnit 5 Tests -->
 			<plugin>
-				<groupId>org.springframework.boot</groupId>
-				<artifactId>spring-boot-maven-plugin</artifactId>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-surefire-plugin</artifactId>
+				<version>${maven-surefire-plugin.version}</version>
+				<configuration>
+					<useModulePath>false</useModulePath>
+				</configuration>
 			</plugin>
 		</plugins>
 	</build>

src/main/java/com/amalvadkar/commons/utils/AmCommonsUtilsApplication.java

@@ -0,0 +1,11 @@
+package com.amalvadkar.commons.utils.constants;
+
+public class StringConstants {
+
+    public static final String EMPTY_STRING = "";
+
+    private StringConstants() {
+        throw new UnsupportedOperationException("Constants class");
+    }
+
+}

src/main/java/com/amalvadkar/commons/utils/constants/StringConstants.java

@@ -0,0 +1,10 @@
+package com.amalvadkar.commons.utils.exceptions;
+
+/**
+ * Custom exception for invalid string operations.
+ */
+public class InvalidStringException extends RuntimeException {
+    public InvalidStringException(String message) {
+        super(message);
+    }
+}

src/main/java/com/amalvadkar/commons/utils/exceptions/InvalidStringException.java

@@ -0,0 +1,71 @@
+package com.amalvadkar.commons.utils.string;
+
+import com.amalvadkar.commons.utils.constants.StringConstants;
+import com.amalvadkar.commons.utils.exceptions.InvalidStringException;
+
+/**
+ * Utility class for common string operations.
+ */
+public final class StringUtils {
+
+    private StringUtils() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    /**
+     * Capitalizes the first letter of the input string.
+     *
+     * @param input The string to capitalize.
+     * @return Capitalized string or an empty string if input is null/empty.
+     * @throws InvalidStringException if the input is null or empty.
+     */
+    public static String capitalize(String input) {
+        if (isEmpty(input)) {
+            throw new InvalidStringException("Input string cannot be null or empty.");
+        }
+        return input.substring(0, 1).toUpperCase() + input.substring(1);
+    }
+
+    /**
+     * Checks if a string is null or empty.
+     *
+     * @param input The string to check.
+     * @return True if the string is null or empty, otherwise false.
+     */
+    public static boolean isEmpty(String input) {
+        return input == null || input.trim().isEmpty();
+    }
+
+    /**
+     * Reverses a given string.
+     *
+     * @param input The string to reverse.
+     * @return The reversed string.
+     */
+    public static String reverse(String input) {
+        if (isEmpty(input)) {
+            return StringConstants.EMPTY_STRING;
+        }
+        return new StringBuilder(input).reverse().toString();
+    }
+
+    /**
+     * Trims spaces from both ends of the string.
+     *
+     * @param input The string to trim.
+     * @return The trimmed string.
+     */
+    public static String trim(String input) {
+        return isEmpty(input) ? StringConstants.EMPTY_STRING : input.trim();
+    }
+
+    /**
+     * Checks if a string contains only letters.
+     *
+     * @param input The string to check.
+     * @return True if the string contains only letters, otherwise false.
+     */
+    public static boolean containsOnlyLetters(String input) {
+        return !isEmpty(input) && input.matches("[a-zA-Z]+");
+    }
+}

src/main/java/com/amalvadkar/commons/utils/string/StringUtils.java

@@ -0,0 +1,59 @@
+package com.amalvadkar.commons.utils.string;
+
+import com.amalvadkar.commons.utils.exceptions.InvalidStringException;
+import common.AbstractUnitTest;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class StringUtilsTest extends AbstractUnitTest {
+
+    @Test
+    void capitalize_should_capitalize_first_letter() {
+        assertThat(StringUtils.capitalize("hello")).isEqualTo("Hello");
+    }
+
+    @Test
+    void capitalize_should_throw_exception_when_input_is_null() {
+        assertThatThrownBy(() -> StringUtils.capitalize(null))
+                .isInstanceOf(InvalidStringException.class)
+                .hasMessage("Input string cannot be null or empty.");
+    }
+
+    @Test
+    void is_empty_should_return_true_when_string_is_empty() {
+        assertThat(StringUtils.isEmpty("")).isTrue();
+    }
+
+    @Test
+    void is_empty_should_return_false_when_string_is_not_empty() {
+        assertThat(StringUtils.isEmpty("test")).isFalse();
+    }
+
+    @Test
+    void reverse_should_return_reversed_string() {
+        assertThat(StringUtils.reverse("hello")).isEqualTo("olleh");
+    }
+
+    @Test
+    void reverse_should_return_empty_when_input_is_empty() {
+        assertThat(StringUtils.reverse("")).isEqualTo("");
+    }
+
+    @Test
+    void trim_should_remove_leading_and_trailing_spaces() {
+        assertThat(StringUtils.trim("  hello  ")).isEqualTo("hello");
+    }
+
+    @Test
+    void contains_only_letters_should_return_true_when_only_letters() {
+        assertThat(StringUtils.containsOnlyLetters("Hello")).isTrue();
+    }
+
+    @Test
+    void contains_only_letters_should_return_false_when_contains_numbers() {
+        assertThat(StringUtils.containsOnlyLetters("Hello123")).isFalse();
+    }
+
+}

src/main/resources/application.properties

@@ -0,0 +1,7 @@
+package common;
+
+import org.junit.jupiter.api.Tag;
+
+@Tag("unit")
+public class AbstractUnitTest {
+}