Improvement on Exceptions on DAO

WEB-INF/src/DAO/IngredientDAO.java

 package DAO;
+import Exceptions.IngredientDAOException;
 import POJO.Ingredient;
 
 import java.sql.*;
@@ -20,79 +21,105 @@ public class IngredientDAO {
     private static final String SELECT_ALL_QUERY = "SELECT * FROM ingredients";
     private static final String INSERT_QUERY = "INSERT INTO ingredients(name, price) VALUES (?, ?)";
     private static final String SELECT_BY_ID_QUERY = "SELECT * FROM ingredients WHERE id = ?";
+    private static final String DELETE_QUERY = "DELETE FROM ingredients WHERE id = ?";
 
     // Method to establish database connection
-    private static void connect() throws SQLException {
-        connection = DriverManager.getConnection(url, user, password);
+    // Method to establish database connection
+    private static void connect() throws IngredientDAOException {
+        try {
+            connection = DriverManager.getConnection(url, user, password);
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error establishing database connection", e);
+        }
     }
 
     // Method to close database connection
-    private static void close() throws SQLException {
-        if (resultSet != null) {
-            resultSet.close();
-        }
-        if (preparedStatement != null) {
-            preparedStatement.close();
-        }
-        if (connection != null) {
-            connection.close();
+    private static void close() throws IngredientDAOException {
+        try {
+            if (resultSet != null) {
+                resultSet.close();
+            }
+            if (preparedStatement != null) {
+                preparedStatement.close();
+            }
+            if (connection != null) {
+                connection.close();
+            }
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error closing database resources", e);
         }
     }
 
     // Method to retrieve all ingredients from the database
-    public static List<Ingredient> getAllIngredients() throws SQLException {
+    public List<Ingredient> getAllIngredients() throws IngredientDAOException {
         List<Ingredient> ingredients = new ArrayList<>();
-        connect();
-        preparedStatement = connection.prepareStatement(SELECT_ALL_QUERY);
-        resultSet = preparedStatement.executeQuery();
+        try {
+            connect();
+            preparedStatement = connection.prepareStatement(SELECT_ALL_QUERY);
+            resultSet = preparedStatement.executeQuery();
 
-        while (resultSet.next()) {
-            int id = resultSet.getInt("id");
-            String name = resultSet.getString("name");
-            double price = resultSet.getDouble("price");
-            Ingredient ingredient = new Ingredient(id, name, price);
-            ingredients.add(ingredient);
+            while (resultSet.next()) {
+                int id = resultSet.getInt("id");
+                String name = resultSet.getString("name");
+                double price = resultSet.getDouble("price");
+                Ingredient ingredient = new Ingredient(id, name, price);
+                ingredients.add(ingredient);
+            }
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error fetching ingredients", e);
+        } finally {
+            close();
         }
-
-        close();
         return ingredients;
     }
 
     // Method to insert a new ingredient into the database
-    public static void insertIngredient(Ingredient ingredient) throws SQLException {
-        connect();
-        preparedStatement = connection.prepareStatement(INSERT_QUERY);
-        preparedStatement.setString(1, ingredient.getName());
-        preparedStatement.setDouble(2, ingredient.getPrice());
-        preparedStatement.executeUpdate();
-        close();
+    public static void insertIngredient(Ingredient ingredient) throws IngredientDAOException {
+        try {
+            connect();
+            preparedStatement = connection.prepareStatement(INSERT_QUERY);
+            preparedStatement.setString(1, ingredient.getName());
+            preparedStatement.setDouble(2, ingredient.getPrice());
+            preparedStatement.executeUpdate();
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error inserting ingredient", e);
+        } finally {
+            close();
+        }
     }
 
     // Method to retrieve an ingredient by its ID
-    public static Ingredient getIngredient(int id) throws SQLException {
-        connect();
-        preparedStatement = connection.prepareStatement(SELECT_BY_ID_QUERY);
-        preparedStatement.setInt(1, id);
-        resultSet = preparedStatement.executeQuery();
-
+    public static Ingredient getIngredient(int id) throws IngredientDAOException {
         Ingredient ingredient = null;
-        if (resultSet.next()) {
-            String name = resultSet.getString("name");
-            double price = resultSet.getDouble("price");
-            ingredient = new Ingredient(id, name, price);
-        }
+        try {
+            connect();
+            preparedStatement = connection.prepareStatement(SELECT_BY_ID_QUERY);
+            preparedStatement.setInt(1, id);
+            resultSet = preparedStatement.executeQuery();
 
-        close();
+            if (resultSet.next()) {
+                String name = resultSet.getString("name");
+                double price = resultSet.getDouble("price");
+                ingredient = new Ingredient(id, name, price);
+            }
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error fetching ingredient", e);
+        } finally {
+            close();
+        }
         return ingredient;
     }
 
-    public void deleteIngredient(int id) throws SQLException {
-        String deleteQuery = "DELETE FROM ingredients WHERE id = ?";
-        try (Connection connection = DriverManager.getConnection(url, user, password);
-             PreparedStatement statement = connection.prepareStatement(deleteQuery)) {
-            statement.setInt(1, id);
-            statement.executeUpdate();
+    public void deleteIngredient(int id) throws IngredientDAOException {
+        try {
+            connect();
+            preparedStatement = connection.prepareStatement(DELETE_QUERY);
+            preparedStatement.setInt(1, id);
+            preparedStatement.executeUpdate();
+        } catch (SQLException e) {
+            throw new IngredientDAOException("Error deleting ingredient", e);
+        } finally {
+            close();
         }
     }
-
 }

WEB-INF/src/Exceptions/IngredientDAOException.java

+package Exceptions;
+
+public class IngredientDAOException extends Exception {
+    public IngredientDAOException(String message, Throwable cause) {
+        super(message, cause);
+    }
+}

WEB-INF/src/Servlets/IngredientServlet.java

@@ -4,7 +4,7 @@ package Servlets;
 
 import DAO.IngredientDAO;
 import POJO.Ingredient;
-import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.*;
 
 import javax.servlet.ServletException;
 import javax.servlet.annotation.WebServlet;