Implement database connection

DzieCoin.iml

@@ -11,5 +11,7 @@
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="library" name="mysql.connector.java" level="project" />
+    <orderEntry type="library" name="Maven: mysql:mysql-connector-java:8.0.30" level="project" />
   </component>
 </module>

pom.xml

@@ -13,4 +13,12 @@
         <maven.compiler.target>19</maven.compiler.target>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     </properties>
+
+    <dependencies>
+        <dependency>
+            <groupId>mysql</groupId>
+            <artifactId>mysql-connector-java</artifactId>
+            <version>8.0.30</version>
+        </dependency>
+    </dependencies>
 </project>

src/main/java/pl/mikorosa/dziecoin/Main.java

@@ -1,5 +1,6 @@
 package pl.mikorosa.dziecoin;
 
+import pl.mikorosa.dziecoin.database.DatabaseConnection;
 import pl.mikorosa.dziecoin.gui.MainFrame;
 
 import java.util.ArrayList;
@@ -8,8 +9,15 @@ import java.util.List;
 public class Main {
     public static int difficulty;
     public static Blockchain blockchain;
+    public static DatabaseConnection db;
 
     public static void main(String[] args) {
+        db = new DatabaseConnection();
+
+        System.out.println(db.query("SELECT * FROM blocks"));
+        System.out.println(db.query("SELECT * FROM transactions"));
+        System.out.println(db.query("SELECT * FROM nfts"));
+
         Wallet w1 = new Wallet();
         Wallet w2 = new Wallet();
         Wallet w3 = new Wallet();

src/main/java/pl/mikorosa/dziecoin/database/DatabaseConnection.java

@@ -0,0 +1,100 @@
+package pl.mikorosa.dziecoin.database;
+
+import java.sql.*;
+import java.util.ArrayList;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+
+public class DatabaseConnection {
+    private Connection connection = null;
+    private Statement statement = null;
+    public DatabaseConnection() {
+        System.out.println("Connecting to database...");
+        try {
+            Class.forName("com.mysql.cj.jdbc.Driver");
+            connection = DriverManager.getConnection("jdbc:mysql://helium.mikorosa.pl:3306/dziecoin", "dziecoin", "Y6seMx#HwgYU");
+            System.out.println("Connected");
+        } catch(ClassNotFoundException e) {
+            System.out.println("Error while setting up JDBC driver: " + e.getMessage());
+            e.printStackTrace();
+        } catch(SQLException e) {
+            System.out.println("Error while connecting to database: " + e.getMessage());
+            e.printStackTrace();
+        }
+    }
+
+    public List<Map<String, Object>> query(String sql) {
+        List<Map<String, Object>> list = new ArrayList<>();
+        try {
+            System.out.println("Executing query " + sql);
+            statement = connection.createStatement();
+            ResultSet result = statement.executeQuery(sql);
+            ResultSetMetaData metaData = result.getMetaData();
+            int columnCount = metaData.getColumnCount();
+
+            while(result.next()) {
+                Map<String, Object> record = new HashMap<>();
+                for(int i = 1; i <= columnCount; i++) {
+                    String columnName = metaData.getColumnName(i);
+                    int columnType = metaData.getColumnType(i);
+                    Object value = null;
+                    switch(columnType) {
+                        case Types.INTEGER:
+                            value = result.getInt(i);
+                            break;
+                        case Types.VARCHAR:
+                        case Types.NVARCHAR:
+                            value = result.getString(i);
+                            break;
+                        default:
+                            value = result.getObject(i);
+                            break;
+                    }
+                    record.put(columnName, value);
+                }
+                list.add(record);
+            }
+        } catch(SQLException e) {
+            System.out.println("Failed to execute query (" + sql + "): " + e.getMessage());
+            e.printStackTrace();
+        }
+        return list;
+    }
+
+    public boolean update(String sql) {
+        try {
+            System.out.println("Executing query " + sql);
+            statement = connection.createStatement();
+            int modifiedRows = statement.executeUpdate(sql);
+
+            if(modifiedRows > 0) return true;
+        } catch(SQLException e) {
+            System.out.println("Failed to execute query (" + sql + "): " + e.getMessage());
+            e.printStackTrace();
+        }
+        return false;
+    }
+
+    public void resetCounter(String tableName) {
+        try {
+            System.out.println("Executing query ALTER TABLE " + tableName + " AUTO_INCREMENT=1");
+            statement = connection.createStatement();
+            statement.execute("ALTER TABLE " + tableName + " AUTO_INCREMENT=1");
+        } catch(SQLException e) {
+            System.out.println("Failed to execute query (ALTER TABLE " + tableName + " AUTO_INCREMENT=1): " + e.getMessage());
+            e.printStackTrace();
+        }
+    }
+
+    public void deleteAllRecords(String tableName) {
+        try {
+            System.out.println("Executing query DELETE FROM " + tableName);
+            statement = connection.createStatement();
+            statement.executeUpdate("DELETE FROM " + tableName);
+        } catch(SQLException e) {
+            System.out.println("Failed to execute query (DELETE FROM " + tableName + "): " + e.getMessage());
+            e.printStackTrace();
+        }
+    }
+}