Java Exercise
In this exercise, you will create a Java program that connects to a database using JDBC. First, you will configure the database connection and then execute an SQL query to retrieve data from a specific table. You will then process the query results and display them in the console. Throughout the exercise, you will learn how to handle exceptions and properly close connections to ensure the application runs smoothly.
Instructions:
- Configure a database connection using JDBC.
- Execute an SQL query to retrieve data from a table.
- Iterate over the query results and display the data to the console.
- Handle any database-related exceptions.
- Make sure to properly close the connection, the
Statement, and the ResultSet.
This exercise will help you understand how to use JDBC to interact with databases in Java, an essential skill for enterprise applications that rely on storing and retrieving data from relational databases.
View Example Code
import java.sql.*;
public class ConnectDatabase {
public static void main(String[] args) {
// Database URL, user, and password
String url = "jdbc:mysql://localhost:3306/my_database";
String user = "root";
String password = "my_password";
// Establish the connection to the database
Connection connection = null;
Statement statement = null;
ResultSet resultSet = null;
try {
connection = DriverManager.getConnection(url, user, password);
System.out.println("Successful connection to the database.");
// Create an SQL query
String query = "SELECT * FROM employees";
statement = connection.createStatement();
resultSet = statement.executeQuery(query);
// Iterate over the results
while (resultSet.next()) {
int id = resultSet.getInt("id");
String name = resultSet.getString("name");
String position = resultSet.getString("position");
// Display the data
System.out.println("ID: " + id + ", Name: " + name + ", Position: " + position);
}
} catch (SQLException e) {
System.out.println("Connection or query error: " + e.getMessage());
} finally {
// Explicitly close the resources
try {
if (resultSet != null) resultSet.close();
if (statement != null) statement.close();
if (connection != null) connection.close();
} catch (SQLException e) {
System.out.println("Error closing resources: " + e.getMessage());
}
}
}
}
Output:
Successful connection to the database.
ID: 1, Name: Juan Perez, Position: Manager
ID: 2, Name: Ana Lopez, Position: Developer
ID: 3, Name: Luis Gomez, Position: Administrator
This program demonstrates how to connect a Java application to a database using JDBC. The connection is established via the database URL, username, and password. An SQL query is then executed to retrieve data from the employees table, and the results are displayed in the console. The use of try-with-resources ensures that resources such as the connection, statement, and result set are automatically closed after use.