请编写一个用java代码查询的代码实现

好的，我可以帮你编写一个Java代码查询实现的例子：

import java.sql.*;

public class QueryExample {
    public static void main(String[] args) {
        Connection conn = null;
        Statement stmt = null;
        ResultSet rs = null;

        try {
            // Register JDBC driver
            Class.forName("com.mysql.jdbc.Driver");

            // Open a connection
            System.out.println("Connecting to database...");
            conn = DriverManager.getConnection("jdbc:mysql://localhost/test", "username", "password");

            // Execute a query
            System.out.println("Creating statement...");
            stmt = conn.createStatement();
            String sql;
            sql = "SELECT id, name, age FROM users";
            rs = stmt.executeQuery(sql);

            // Extract data from result set
            while (rs.next()) {
                // Retrieve by column name
                int id = rs.getInt("id");
                String name = rs.getString("name");
                int age = rs.getInt("age");

                // Display values
                System.out.print("ID: " + id);
                System.out.print(", Name: " + name);
                System.out.println(", Age: " + age);
            }
            // Clean-up environment
            rs.close();
            stmt.close();
            conn.close();
        } catch (SQLException se) {
            // Handle errors for JDBC
            se.printStackTrace();
        } catch (Exception e) {
            // Handle errors for Class.forName
            e.printStackTrace();
        } finally {
            // Finally block used to close resources
            try {
                if (stmt != null)
                    stmt.close();
            } catch (SQLException se2) {
            } // nothing we can do
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException se) {
                se.printStackTrace();
            }
        }
        System.out.println("Goodbye!");
    }
}

上述代码实现了从数据库中查询用户表中的id、name和age字段，并将结果输出到控制台中。你可以将上述代码改为你所使用的数据库和表结构，以适应你的需求。