java编写数据库系统

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DatabaseConnector {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "username";
        String password = "password";

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            System.out.println("Connected to the database!");
        } catch (SQLException e) {
            System.err.println("Failed to connect to the database: " + e.getMessage());
        }
    }
}

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

public class SafeQueryExample {
    public static void main(String[] args) {
        String url = "jdbc:mysql://localhost:3306/mydatabase";
        String user = "username";
        String password = "password";
        String userInput = "some user input"; // 假设这是从用户获取的输入

        try (Connection conn = DriverManager.getConnection(url, user, password)) {
            String sql = "SELECT * FROM users WHERE username = ?";
            try (PreparedStatement pstmt = conn.prepareStatement(sql)) {
                pstmt.setString(1, userInput);
                pstmt.executeQuery();
            }
        } catch (SQLException e) {
            System.err.println("Database error: " + e.getMessage());
        }
    }
}