JDBC

In simple words#

Learning objectives#

• Connect to a database
• Query with PreparedStatement
• Map ResultSet rows to records
• Use transactions

Explanation#

Add the driver dependency (e.g. com.microsoft.sqlserver:mssql-jdbc, org.postgresql:postgresql).

Get a Connection from DriverManager or, in real apps, a connection pool (HikariCP).

PreparedStatement with ? placeholders prevents SQL injection and handles types correctly.

conn.setAutoCommit(false) + commit/rollback groups changes into a transaction. Use try-with-resources for everything.

Code example: Querying products safely#

1import java.sql.*;
2import java.util.ArrayList;
3import java.util.List;
4

5record Product(int id, String name, double price) {}
6

7public class ProductDao {
8    private static final String URL =
9        "jdbc:sqlserver://localhost:1433;databaseName=ShopDB;encrypt=true;trustServerCertificate=true";
10

11    static List<Product> findCheaperThan(double maxPrice) throws SQLException {
12        String sql = "SELECT Id, Name, Price FROM Products WHERE Price < ? ORDER BY Price";
13        try (Connection conn = DriverManager.getConnection(URL, System.getenv("DB_USER"), System.getenv("DB_PASSWORD"));
14             PreparedStatement ps = conn.prepareStatement(sql)) {
15            ps.setDouble(1, maxPrice);
16            try (ResultSet rs = ps.executeQuery()) {
17                List<Product> list = new ArrayList<>();
18                while (rs.next()) list.add(new Product(rs.getInt("Id"), rs.getString("Name"), rs.getDouble("Price")));
19                return list;
20            }
21        }
22    }
23

24    public static void main(String[] args) throws SQLException {
25        findCheaperThan(5000).forEach(System.out::println);
26    }
27}

Product[id=2, name=Mouse, price=1400.0]
Product[id=3, name=Keyboard, price=2200.0]

This example is illustrative. Copy or download it and run it in your own environment; the expected output is shown above.

Step-by-step explanation#

1. Credentials come from environment variables.
2. The ? placeholder is filled with setDouble.
3. rs.next() moves through rows; columns map to a record.
4. try-with-resources closes connection, statement and result set.

Real-world use case#

Common mistakes#

Best practices#

• PreparedStatement always
• Connection pool in apps
• try-with-resources
• Credentials from environment or vault

Remember this#

Practice exercise#

1try (var ps = conn.prepareStatement("INSERT INTO Products (Name, Price) VALUES (?, ?)")) {
2    ps.setString(1, "Webcam");
3    ps.setDouble(2, 3200);
4    ps.executeUpdate();
5}

Mini quiz#

Want more? Practise all Java MCQs · Java interview questions

Related topics#

My notes#

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