Created a new Payment Service which will store the data in SQL

design-patterns/pom.xml

@@ -13,5 +13,26 @@
         <maven.compiler.target>21</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
+    <dependencies>
+        <!-- MySQL Connector -->
+        <dependency>
+            <groupId>mysql</groupId>
+            <artifactId>mysql-connector-java</artifactId>
+            <version>8.0.33</version>
+            <scope>runtime</scope>  <!-- Ensures it's only used at runtime -->
+        </dependency>
+
+        <!-- Logging (Optional but Recommended) -->
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-api</artifactId>
+            <version>1.7.36</version>
+        </dependency>
+        <dependency>
+            <groupId>org.slf4j</groupId>
+            <artifactId>slf4j-simple</artifactId>
+            <version>1.7.36</version>
+        </dependency>
+    </dependencies>
 
 </project>

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/Card.java

@@ -0,0 +1,11 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public class Card {
+    String cardNo;
+    String userName;
+
+    public Card(String cardNo, String userName) {
+        this.cardNo = cardNo;
+        this.userName = userName;
+    }
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/CreditCard.java

@@ -0,0 +1,11 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public class CreditCard extends Card implements PaymentMethod {
+    public CreditCard(String cardNo, String name) {
+        super(cardNo, name);
+    }
+
+    public void pay() {
+        System.out.println("Making payment via Credit Card");
+    }
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/DebitCard.java

@@ -0,0 +1,12 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public class DebitCard extends Card implements PaymentMethod {
+    public DebitCard(String cardNo, String userName) {
+        super(cardNo, userName);
+    }
+
+    @Override
+    public void pay() {
+        System.out.println("Making payment via Debit Card");
+    }
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/PaymentMethod.java

@@ -0,0 +1,5 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public interface PaymentMethod {
+    void pay();
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/PaymentService.java

@@ -0,0 +1,107 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+import java.sql.*;
+
+public class PaymentService {
+    private static PaymentService instance;
+    private Connection connection;
+
+    // Singleton Constructor
+    private PaymentService() {
+        try {
+            this.connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/testdatabase", "root", "AdminSandeep");
+            createTableIfNotExists();
+        } catch (Exception e) {
+            throw new RuntimeException("Database connection failed!", e);
+        }
+    }
+
+    public static synchronized PaymentService getInstance() {
+        if (instance == null) {
+            instance = new PaymentService();
+        }
+        return instance;
+    }
+
+    // Ensures Table Exists
+    private void createTableIfNotExists() {
+        try (Statement stmt = connection.createStatement()) {
+            String sql = "CREATE TABLE IF NOT EXISTS payment_methods (" +
+                    "id INT AUTO_INCREMENT PRIMARY KEY, " +
+                    "name VARCHAR(255) UNIQUE NOT NULL, " +
+                    "type ENUM('CREDIT_CARD', 'DEBIT_CARD', 'UPI') NOT NULL, " +
+                    "details TEXT NOT NULL)";
+            stmt.executeUpdate(sql);
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    // Add Payment Method with ENUM
+    public void addPaymentMethod(String name, PaymentMethod pm) {
+        try {
+            PaymentType type;
+            String details;
+
+            if (pm instanceof CreditCard) {
+                type = PaymentType.CREDIT_CARD;
+                details = ((CreditCard) pm).cardNo;
+            } else if (pm instanceof DebitCard) {
+                type = PaymentType.DEBIT_CARD;
+                details = ((DebitCard) pm).cardNo;
+            } else if (pm instanceof UPI) {
+                type = PaymentType.UPI;
+                details = ((UPI) pm).upiId;
+            } else {
+                throw new IllegalArgumentException("Unknown Payment Method");
+            }
+
+            PreparedStatement stmt = connection.prepareStatement(
+                    "INSERT INTO payment_methods (name, type, details) VALUES (?, ?, ?) " +
+                            "ON DUPLICATE KEY UPDATE type=VALUES(type), details=VALUES(details)");
+
+            stmt.setString(1, name);
+            stmt.setString(2, type.name()); // Store ENUM as String
+            stmt.setString(3, details);
+            stmt.executeUpdate();
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+
+    // Retrieve and Make Payment
+    public void makePayment(String name) {
+        try {
+            PreparedStatement stmt = connection.prepareStatement(
+                    "SELECT type, details FROM payment_methods WHERE name = ?");
+            stmt.setString(1, name);
+            ResultSet rs = stmt.executeQuery();
+
+            if (rs.next()) {
+                PaymentType type = PaymentType.valueOf(rs.getString("type")); // Convert DB String to Enum
+                String details = rs.getString("details");
+
+                PaymentMethod pm;
+                switch (type) {
+                    case CREDIT_CARD:
+                        pm = new CreditCard(details, name);
+                        break;
+                    case DEBIT_CARD:
+                        pm = new DebitCard(details, name);
+                        break;
+                    case UPI:
+                        pm = new UPI(details, name);
+                        break;
+                    default:
+                        throw new IllegalArgumentException("Unknown Payment Type");
+                }
+
+                pm.pay();
+            } else {
+                throw new IllegalArgumentException("Payment method not found: " + name);
+            }
+        } catch (Exception e) {
+            e.printStackTrace();
+        }
+    }
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/PaymentType.java

@@ -0,0 +1,5 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public enum PaymentType {
+    CREDIT_CARD, DEBIT_CARD, UPI, WALLET;
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Basics/UPI.java

@@ -0,0 +1,15 @@
+package org.prateek.PaymentServiceDb.Basics;
+
+public class UPI implements PaymentMethod {
+    String upiId;
+    String userName;
+
+    public UPI(String upiId, String userName) {
+        this.upiId = upiId;
+        this.userName = userName;
+    }
+
+    public void pay() {
+        System.out.println("Making payment via UPI" + upiId);
+    }
+}

design-patterns/src/main/java/org/prateek/PaymentServiceDb/Client.java

@@ -0,0 +1,26 @@
+package org.prateek.PaymentServiceDb;
+
+import org.prateek.PaymentServiceDb.Basics.CreditCard;
+import org.prateek.PaymentServiceDb.Basics.DebitCard;
+import org.prateek.PaymentServiceDb.Basics.PaymentService;
+import org.prateek.PaymentServiceDb.Basics.UPI;
+
+public class Client {
+    public static void main(String[] args) {
+        System.out.println("Hello, World!");
+        PaymentService ps = PaymentService.getInstance();
+
+        ps.addPaymentMethod("sandeepCreditCardId", new CreditCard("1234", "Sandeep"));
+        ps.addPaymentMethod("JohnCredit", new CreditCard("1234-5678-9876", "John"));
+        ps.addPaymentMethod("JohnUPI", new UPI("john@upi", "John"));
+        ps.makePayment("JohnCredit");
+
+        ps.makePayment("sandeepCreditCardId");
+        ps.addPaymentMethod("sgDebitCardId", new DebitCard("5678", "Sandeep"));
+        ps.makePayment("sgDebitCardId");
+        ps.addPaymentMethod("SgUPIID", new UPI("sg@okhdfcbank", "Sandeep"));
+        ps.makePayment("SgUPIID");
+
+    }
+}
+