Insertion functionality and code refactoring

Author: akash-coded

jdbc/JDBCDemo/src/App.java

@@ -7,7 +7,9 @@ public static void main(String[] args) {
             Class.forName("com.mysql.cj.jdbc.Driver");
 
             CityController cities = new CityController();
-            cities.index();
+            cities.create();
+            cities.read(); // prints the details of all cities
+            cities.readOne(); // prints the details of one city
         } catch (Exception e) {
             System.out.println("Some error occurred in the application " + e);
         }

jdbc/JDBCDemo/src/controllers/CityController.java

@@ -1,24 +1,38 @@
 package controllers;
 
 import java.sql.ResultSet;
-import java.sql.SQLException;
 import models.City;
 
+/**
+ * Controller class for operations on city table
+ */
 public class CityController {
-    public void index() { // Read operation
-        try {
-            ResultSet result = City.fetchTenCities();
-            System.out.println("Id\tName\tCountryCode\tDistrict\tPopulation");
-            while (result != null && result.next()) {
-                int id = result.getInt(1);
-                String name = result.getString(2);
-                String countryCode = result.getString(3);
-                String district = result.getString(4);
-                int population = result.getInt(5);
-                System.out.println(id + "\t" + name + "\t" + countryCode + "\t" + district + "\t" + population);
-            }
-        } catch (SQLException | NullPointerException e) {
-            System.out.println("Error in reading the ResultSet");
-        }
+    /**
+     * Retrieves the details of all the cities and prints them
+     */
+    public void read() {
+        ResultSet result = City.fetchAllCityDetails();
+        City.printCityDetails(result);
     }
+
+    /**
+     * Retrieves the details of the city correspondinf to the id
+     */
+    public void readOne() {
+        ResultSet result = City.fetchCityDetailsById(4500);
+        City.printCityDetails(result);
+    }
+
+    public void create() {
+        int rowsAffected = City.insertCity(4500, "Old Delhi", "IND", "Delhi", 12737);
+        System.out.println(rowsAffected + " records were inserted");
+    }
+
+    // public int update() {
+
+    // }
+
+    // public int delete() {
+
+    // }
 }

jdbc/JDBCDemo/src/models/City.java

@@ -6,24 +6,38 @@
 public class City {
     private static final Connection connection = ConnectionManager.getConnection();
 
-    public static ResultSet fetchTenCities() {
+    public static void printCityDetails(ResultSet result) {
+        if (result != null) {
+            System.out.println("\nId\tName\tCountryCode\tDistrict\tPopulation");
+            try {
+                if (!result.next()) {
+                    System.out.println("Empty set!");
+                } else {
+                    do {
+                        int id = result.getInt(1);
+                        String name = result.getString(2);
+                        String countryCode = result.getString(3);
+                        String district = result.getString(4);
+                        int population = result.getInt(5);
+                        System.out.println(id + "\t" + name + "\t" + countryCode + "\t" + district + "\t" + population);
+                    } while (result.next());
+                }
+            } catch (SQLException | NullPointerException e) {
+                System.out.println("Error while printing the city details: " + e);
+            }
+        } else {
+            System.out.println("ResultSet null");
+        }
+    }
+
+    public static ResultSet fetchAllCityDetails() {
         ResultSet result = null;
         String sql = "SELECT * FROM city LIMIT ?";
         try {
             PreparedStatement preparedStatement = connection.prepareStatement(sql);
             preparedStatement.setInt(1, 10);
             try {
                 result = preparedStatement.executeQuery();
-                // System.out.println("Printed from model");
-                // while (result != null && result.next()) {
-                // int id = result.getInt(1);
-                // String name = result.getString(2);
-                // String countryCode = result.getString(3);
-                // String district = result.getString(4);
-                // int population = result.getInt(5);
-                // System.out.println(id + "\t" + name + "\t" + countryCode + "\t" + district +
-                // "\t" + population);
-                // }
             } catch (SQLException e) {
                 System.out.println("Error in the resultset " + e);
             }
@@ -32,4 +46,49 @@ public static ResultSet fetchTenCities() {
         }
         return result;
     }
+
+    /**
+     * Retrieves the details of one city by its id
+     * 
+     * @param id int
+     * @return ResultSet
+     */
+    public static ResultSet fetchCityDetailsById(int id) {
+        ResultSet result = null;
+        String sql = "SELECT * FROM city WHERE id = ?";
+        try {
+            PreparedStatement preparedStatement = connection.prepareStatement(sql);
+            preparedStatement.setInt(1, id);
+            try {
+                result = preparedStatement.executeQuery();
+            } catch (SQLException e) {
+                System.out.println("Error in the resultset " + e);
+            }
+        } catch (SQLException e) {
+            System.out.println("Error obtaining an instance of the statement " + e);
+        }
+        return result;
+    }
+
+    public static int insertCity(int id, String name, String countryCode, String district, int population) {
+        int rowsAffected = 0;
+        String sql = "insert into city (Id, Name, CountryCode, District, Population) VALUES (?, ?, ?, ?, ?)";
+        try {
+            PreparedStatement statement = connection.prepareStatement(sql);
+            statement.setInt(1, id);
+            statement.setString(2, name);
+            statement.setString(3, countryCode);
+            statement.setString(4, district);
+            statement.setInt(5, population);
+            try {
+                rowsAffected = statement.executeUpdate();
+            } catch (SQLException e) {
+                System.out.println("Error during insertion " + e);
+            }
+        } catch (SQLException e) {
+            System.out.println("Error obtaining an instance of the statement " + e);
+        }
+        return rowsAffected;
+    }
+
 }