分别针对Customers表与Order表的通用查询操作

1.针对customers表通用的查询操作

CustomerForQuery

package com.aff.PreparedStatement;

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import org.junit.Test;

import com.aff.bean.Customer;
import com.aff.utils.JDBCUtils;

//对于Customers表的查询操作
public class CustomerForQuery {
    @Test
    public void testqueryForCustomers() {
        String sql = "select id,name,email from customers where id =?";
        Customer customer = queryForCustomers(sql, 12);
        System.out.println(customer);
        
    }

    // 针对customers表通用的查询操作
    public Customer queryForCustomers(String sql, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        // 结果集
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            // 预编译
            ps = conn.prepareStatement(sql);
            // 填充占位符
            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
            ResultSetMetaData rsmd = rs.getMetaData();
            // 通过ResultSetMetaData获取结果集中的列数
            int columnCount = rsmd.getColumnCount();
            if (rs.next()) {
                // 对象调一次就行了,一条数据，只造一个对象
                Customer cust = new Customer();
                for (int i = 0; i < columnCount; i++) {
                    // 处理结果集，也就是表中的一行中的每一个列
                    Object columvalue = rs.getObject(i + 1);// 获取列值
                    String columName = rsmd.getColumnName(i + 1);// 获取列名

                    // 给cust对象指定的columName属性，赋值为columvalue,通过反射完成
                    // 把名为columName的属性拿到，因为表中列名和属性是对应的
                    Field field = Customer.class.getDeclaredField(columName);// 和列名相同的属性
                    field.setAccessible(true);// 可能是私有的，这样设置使的能够访问

                    // 把这个属性名的值设置给当前的cust，赋值为columvalue
                    field.set(cust, columvalue);
                }
                return cust;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }
        return null;
    }

    @Test
    public void tesQuery() {
        Connection conn = null;
        PreparedStatement ps = null;
        // 执行，并返回一个结果集
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            String sql = "select id ,name, email,birth from customers where id =?";
            ps = conn.prepareStatement(sql);
            ps.setObject(1, 1);

            rs = ps.executeQuery();
            // 处理结果集
            if (rs.next()) {//判断结果集的下一条是否有数据，如果有数据返回true，并指针下移，
                            //返回false指针不下移,直接结束
                int id = rs.getInt(1);
                String name = rs.getString(2);
                String email = rs.getString(3);
                Date birth = rs.getDate(4);
                // 方式一
                // System.out.println("id = " + id + ",name = " + name + ",email
                // = "
                // + email + ",birth = " + birth);

                // 方式二
                // Object[] data = new Object[] { id, name, email, birth };

                // 方式三
                Customer customer = new Customer(id, name, email, birth);
                System.out.println(customer);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        // 关闭资源
        JDBCUtils.closeResource(conn, ps, rs);
    }
}

2.针对Order表的通用查询

OrderForQuery

package com.aff.PreparedStatement;

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import org.junit.Test;

import com.aff.bean.Order;
import com.aff.utils.JDBCUtils;

//针对Order表的通用查询
public class OrderForQuery {
    /*
     * 针对表的字段名与类的属性名不相同的情况
     *  1.必须声明sql时，使用的类的属性名用来命名字段的别名
     *  2.使用ResultSetMetaData时，需要使用getColumnLabel()来替换getColumnName()方法，获取类的别名
     *  说明： sql中没有给字段起别名，那么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Order表的通用查询
    public Order orderForQuery(String sql, Object... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            // 执行,获取结果集
            ps = conn.prepareStatement(sql);
            // 填充占位符
            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();
            // 获取列数
            int columnCount = rsmd.getColumnCount();
            if (rs.next()) {

                Order order = new Order();
                for (int i = 0; i < columnCount; i++) {
                    // 获取每个列的列值
                    Object columnValue = rs.getObject(i + 1);

                    // 获取列的列名,列数 列名为元数据用来修饰ResultSet(结果集)的，
                    // String columnName = rsmd.getColumnName(i + 1);-- 不推荐使用
                    // 改为获取列的别名
                    String ColumnLabel = rsmd.getColumnLabel(i+1);

                    // 通过反射将对象指定名columnName的属性赋给指定的值columnValue
                    // 先拿到class
                    Field field = Order.class.getDeclaredField(ColumnLabel);
                    field.setAccessible(true);
                    field.set(order, columnValue);
                }
                return order;
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }
        return null;
    }

    @Test
    public void testQuery1() {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection();
            String sql = "select order_id, order_name,order_date from `order` where order_id = ?";
            ps = conn.prepareStatement(sql);
            // 查询id = 1数据
            ps.setObject(1, 1);
            rs = ps.executeQuery();
            if (rs.next()) {
                // 对应表中一行三列数据
                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 (Exception e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.closeResource(conn, ps, rs);
        }
    }
}

Customer

package com.aff.bean;

import java.sql.Date;

//ORM编程思想   Object  relational  mapping
//一个数据表对应一个java类
//表中的一条记录对应java类的一个对象
//表中的一个字段对应java类的一个属性
//java.sql.Date -------------- Date  sql类型
public class Customer {
    private int id;
    private String name;
    private String email;
    private Date birth;
    public Customer() {
        super();
        // TODO Auto-generated constructor stub
    }
    public Customer(int id, String name, String email, Date birth) {
        super();
        this.id = id;
        this.name = name;
        this.email = email;
        this.birth = birth;
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public String getEmail() {
        return email;
    }
    public void setEmail(String email) {
        this.email = email;
    }
    public Date getBirth() {
        return birth;
    }
    public void setBirth(Date birth) {
        this.birth = birth;
    }
    @Override
    public String toString() {
        return "Customer [id=" + id + ", name=" + name + ", email=" + email + ", birth=" + birth + "]";
    }
    
}

Order

package com.aff.bean;

import java.sql.Date;

public class Order {
    private int orderId;
    private String orderName;
    private Date orderDate;

    public Order() {
        super();
    }

    public Order(int orderId, String orderName, Date orderDate) {
        super();
        this.orderId = orderId;
        this.orderName = orderName;
        this.orderDate = orderDate;
    }

    public int getOrderId() {
        return orderId;
    }

    public void setOrderId(int orderId) {
        this.orderId = orderId;
    }

    public String getOrderName() {
        return orderName;
    }

    public void setOrderName(String orderName) {
        this.orderName = orderName;
    }

    public Date getOrderDate() {
        return orderDate;
    }

    public void setOrderDate(Date orderDate) {
        this.orderDate = orderDate;
    }

    @Override
    public String toString() {
        return "Order [orderId=" + orderId + ", orderName=" + orderName + ", orderDate=" + orderDate + "]";
    }

}