General query operations for Customers table and Order table respectively

1. General query operation for customers table

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;

// Query operations on the Customers table 
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);
        
    }

    // General query operation for customers table 
    public Customer queryForCustomers (String sql, Object ... args) {
        Connection conn = null;
        PreparedStatement ps = null ;
         // Result set 
        ResultSet rs = null ;
         try {
            conn = JDBCUtils.getConnection ();
             // Pre-compiled 
            ps = conn.prepareStatement (sql);
             // Padded placeholder 
            for ( int i = 0; i <args.length; i ++ ) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery ();
             // Get the result set metadata ResultSetMetaData 
            ResultSetMetaData rsmd = rs.getMetaData ();
             // Get the number of columns in the result set through ResultSetMetaData 
            int columnCount = rsmd.getColumnCount ();
             if (rs.next ()) {
                 // The object can be transferred once, one piece of data, only one object is created 
                Customer cust = new Customer ();
                 for ( int i = 0; i <columnCount; i ++ ) {
                     // Process the result set, that is, the table Each column in a row in 
                    Object Columvalue = rs.getObject (i + 1);// Get column value 
                    String columName = rsmd.getColumnName (i + 1); // Get column name

                    // The columnName attribute specified for the cust object is assigned a columnvalue, which is done by reflection.
                     // Get the attribute named columnName, because the column names and attributes in the table are the corresponding 
                    Field field = Customer. Class .getDeclaredField (columName); / / The same property as the column name 
                    field.setAccessible ( true ); // May be private, this setting makes it accessible

                    // Set the value of this property name to the current cust, and assign the value to columnvalue 
                    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 ;
         // Execute and return a result set 
        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 ();
             // Process the result set 
            if (rs.next ()) { // Determine whether the next item in the result set has data, if there is data, return true and move the pointer down, 
                            // return a false pointer Without moving down, directly end 
                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 ();
        }
        // Close resource 
        JDBCUtils.closeResource (conn, ps, rs);
    }
}

 

2. General query for Order table

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;

// General query for Order table 
public  class OrderForQuery {
     / *
     * For the case where the field name of the table is different from the attribute name of the class
     * 1. When SQL must be declared, the attribute name of the class used is used to name the field's alias
     * 2. When using ResultSetMetaData, you need to use getColumnLabel () to replace getColumnName () method to get the class alias
     * Note: There is no alias for the field in sql, then getColumnLabel () gets the column name
     */

    @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);
    }

    // General query for Order table 
    public Order orderForQuery (String sql, Object ... args) {
        Connection conn = null;
        PreparedStatement ps = null;
        ResultSet rs = null;
        try {
            conn = JDBCUtils.getConnection ();
             // Execute, get result set 
            ps = conn.prepareStatement (sql);
             // Fill placeholder 
            for ( int i = 0; i <args.length; i ++ ) {
                ps.setObject(i + 1, args[i]);
            }
            rs = ps.executeQuery ();
             // Get the metadata of the result set 
            ResultSetMetaData rsmd = rs.getMetaData ();
             // Get the number of columns 
            int columnCount = rsmd.getColumnCount ();
             if (rs.next ()) {

                Order order = new Order ();
                 for ( int i = 0; i <columnCount; i ++ ) {
                     // Get the column value of each column 
                    Object columnValue = rs.getObject (i + 1 );

                    // Get the column name of the column, the column number column name is used to modify the ResultSet (result set),
                     // String columnName = rsmd.getColumnName (i + 1);- // It is not recommended
                     // to get the column instead Alias 
                    String ColumnLabel = rsmd.getColumnLabel (i + 1 );

                    // The property of the object named columnName is assigned to the specified value columnValue by reflection
                     // First get the 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);
             // Query id = 1 data 
            ps.setObject (1, 1 );
            rs = ps.executeQuery ();
             if (rs.next ()) {
                 // One row and three columns of data in the corresponding table 
                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 programming ideas Object relational mapping
 // A data table corresponds to a java class
 // A record in the table corresponds to an object of the java class
 // A field in the table corresponds to an attribute of the java class
 // java.sql.Date -------------- Date sql type 
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 + "]";
    }

}