针对customers表的通用查询操作举例

https://www.bilibili.com/video/BV1eJ411c7rf?p=18

import io.github.jihch.bean.Customer;
import io.github.jihch.util.JDBCUtils;
import org.junit.Test;

import java.lang.reflect.Field;
import java.sql.*;

/**
 * 针对于 Customers 表的查询操作
 */
public class CustomerForQuery {

    @Test
    public void testQueryForCustomers() {
        String sql = "select id, name, email, birth from customers where id = ?";
        Customer customer = queryForCustomers(sql, 2);
        System.out.println(customer);

        sql = "select name, email from customers where id = ?";
        customer = queryForCustomers(sql, 2);
        System.out.println(customer);

    }


    /**
     * 针对 customers表的通用的查询操作
     * @param sql
     * @param args
     * @throws Exception
     */
    public Customer queryForCustomers(String sql, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        Customer customer = null;

        try {
            conn = JDBCUtils.getConnection();
            ps = conn.prepareStatement(sql);
            for (int i = 0; i < args.length; i++) {
                ps.setObject(i+1, args[i]);
            }
            rs = ps.executeQuery();
            //获取结果集的元数据
            ResultSetMetaData rsmd = rs.getMetaData();

            //通过 ResultSetMetaData 获取结果集中的列数
            int columnCount = rsmd.getColumnCount();

            if (rs.next()) {

                customer = new Customer();

                //处理结果集一行数据中的每一列
                for (int i = 0; i < columnCount; i++) {

                    //获取每个列的列名
                    String columnName = rsmd.getColumnName(i+1);

                    Object columnValue = rs.getObject(i + 1);

                    //给 customer 对象指定的某个属性，赋值为 value
                    Field field = Customer.class.getDeclaredField(columnName);
                    field.setAccessible(true);
                    field.set(customer, columnValue);

                }

            }//end if

        } catch (SQLException e) {
            throw new RuntimeException(e);

        } catch (Exception e) {
            throw new RuntimeException(e);

        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }

        return customer;
    }

}

Customer{id=2, name='汪峰', email='wf@126.com', birth=2010-02-02}
Customer{id=0, name='汪峰', email='wf@126.com', birth=null}

https://github.com/jihch/jdbc/blob/main/src/main/java/io/github/jihch/preparedstatement/crud/CustomerForQuery.java