针对order表的通用查询操作
https://www.bilibili.com/video/BV1eJ411c7rf?p=19
import io.github.jihch.bean.Order;
import io.github.jihch.util.JDBCUtils;
import org.junit.Test;
import java.lang.reflect.Field;
import java.sql.*;
/**
* 针对于 Order 表的通用的查询操作
*/
public class OrderForQuery {
/**
* 针对于表的字段名与类的属性名不相同的情况
* 1.必须声明 sql 时，使用类的属性名来命名字段的别名
* 2。使用 ResultSetMetaData 时，需要使用 getColumnLabel() 来替换 getColumnName() 获取列的别名
* 说明：如果 sql 中没有给字段起别名，getColumnLabel() 获取的就是列名
*/
@Test
public void testOrderForQuery() {
String sql = "select order_id orderId, order_name orderName, order_date orderDate from `order` where order_id = ?";
Order order = orderForQuery(sql, 1);
System.out.println(order);
}
/**
* 针对于 Order 表的通用查询操作
* @return
*/
public Order orderForQuery(String sql, Object... args) {
Order order = null;
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JDBCUtils.getConnection();
ps = conn.prepareStatement(sql);
for (int i = 0; i < args.length; i++) {
ps.setObject(i+1, args[i]);
}
//执行获取结果集
rs = ps.executeQuery();
//获取结果集的元数据
ResultSetMetaData rsmd = rs.getMetaData();
int columnCount = rsmd.getColumnCount();
if (rs.next()) {
order = new Order();
for (int i = 0; i < columnCount; i++) {
//获取每个列的列值：通过ResultSet
Object value = rs.getObject(i + 1);
//获取每个列的列名：通过ResultSetMetaData
//获取列的列名：getColumnName() --不推荐使用
//获取列的别名：getColumnLabel()
String columnName = rsmd.getColumnName(i + 1);
String columnLabel = rsmd.getColumnLabel(i + 1);
System.out.printf("columnName:%s, columnLabel:%s\n", columnName, columnLabel);
//通过反射，将对象指定名 columnName 的属性赋值为指定的值 columnValue
// Field field = Order.class.getDeclaredField(columnName);
Field field = Order.class.getDeclaredField(columnLabel);
field.setAccessible(true);
field.set(order, value);
}
//获取每个列的列名
}//end if
} catch (SQLException e) {
throw new RuntimeException(e);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
JDBCUtils.closeResource(conn, ps, rs);
}
return order;
}
@Test
public void testQuery1() {
String sql = "select order_id, order_name, order_date from `order` where order_id = ?";
Connection conn = null;
PreparedStatement ps = null;
ResultSet rs = null;
try {
conn = JDBCUtils.getConnection();
ps = conn.prepareStatement(sql);
ps.setObject(1, 1);
rs = ps.executeQuery();
if (rs.next()) {
int id = (int) rs.getObject(1);
String name = (String) rs.getObject(2);
Date date = (Date) rs.getObject(3);
Order order = new Order(id, name, date);
System.out.println(order);
}
} catch (SQLException e) {
throw new RuntimeException(e);
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
JDBCUtils.closeResource(conn, ps, rs);
}
}
}
columnName:order_id, columnLabel:orderId
columnName:order_name, columnLabel:orderName
columnName:order_date, columnLabel:orderDate
Order{orderId=1, orderName='DD', orderDate=2010-03-04}
测试数据表没有数据的情况下，返回的结果集元数据是否包含 columnName、columnLabel
columnName:column1, columnLabel:column1
columnName:column2, columnLabel:column2
columnName:column3, columnLabel:column3
https://www.bilibili.com/video/BV1eJ411c7rf?p=20
