我刚从 JBDC 开始。我需要创建一个 Java/MySQL 插入语句，该语句插入 null、字符串和解析为 int 的字符串（作为用户使用 Scanner 的输入）。我尝试了很多可能性，但到目前为止没有任何效果。编写这样的插入语句的正确方法是什么，或者我应该考虑其他推荐的方法？谢谢你的帮助！
import java.util.ArrayList;
import java.util.Scanner;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class AddBook {
static Scanner keyboard = new Scanner(System.in);
static InvMenu invmenu = new InvMenu();
static MainMenu mainmenu = new MainMenu();
static boolean b = true;
static int x;
static double y;
static double z;
static String choice;
static char letter;
public static void addBook(){
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
System.out.println("+----------------+");
System.out.println("| Add a Book |");
System.out.println("+----------------+\n");
System.out.print("\nEnter ISBN number: ");
String isbn = keyboard.next();
System.out.print("Enter Book Title: ");
String title = keyboard.next();
System.out.print("Enter Author's name: ");
String author = keyboard.next();
System.out.print("Enter Publisher's name: ");
String publisher = keyboard.next();
System.out.print("Enter The Date the Book is Added to the Inventory (MM/DD/YYYY): ");
String dateAdded = keyboard.next();
do{
b = true;
System.out.print("Enter The Quantity of Book Being Added: ");
String qtyOnHand = keyboard.next();
try {
x = Integer.parseInt(qtyOnHand);
}
catch(NumberFormatException nFE) {
b = false;
System.out.println();
System.out.println("--------------------------------------------------------");
System.out.println(" !!! You did not enter a valid value. Try again !!!");
System.out.println("--------------------------------------------------------");
System.out.println();
}
}while(b == false);
do{
b = true;
System.out.print("Enter The Wholesale Cost of the Book: ");
String wholesale = keyboard.next();
try {
y = Double.parseDouble(wholesale);
}
catch(NumberFormatException nFE) {
b = false;
System.out.println("--------------------------------");
System.out.println(" ! Wrong Value. Try again !");
System.out.println("--------------------------------\n");
}
}while(b == false);
do{
b = true;
System.out.print("Enter The Retail Price of the Book: ");
String retail = keyboard.next();
try {
z = Double.parseDouble(retail);
}
catch(NumberFormatException nFE) {
b = false;
System.out.println("--------------------------------");
System.out.println(" ! Wrong Value. Try again !");
System.out.println("--------------------------------\n");
}
}while(b == false);
System.out.println("-------------------------------------------");
System.out.println("ISBN number: " + isbn);
System.out.println("Book Title: " + title);
System.out.println("Author's name: " + author);
System.out.println("Publisher's name: " + publisher);
System.out.println("The Date the Book is Added to the Inventory (MM/DD/YYYY): " + dateAdded);
System.out.println("The Quantity of Book Being Added: " + x);
System.out.printf("The Wholesale Cost of the Book: $ %6.2f\n", y);
System.out.printf("The Retail Price of the Book: $ %6.2f\n", z);
System.out.println("-------------------------------------------\n");
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
String connectionUrl = "jdbc:mysql://localhost:3306/serendipity";
String connectionUser = "root";
String connectionPassword = "password";
conn = DriverManager.getConnection(connectionUrl, connectionUser, connectionPassword);
stmt = conn.createStatement();
stmt.executeUpdate("INSERT INTO books(book_id, isbn, title, author, publisher, dateAdded, qtyOnHand, wholesale, retail) VALUES ('"+null+ "','" +isbn+ " ','" +title+ " ',' " +author+ " ',' " +publisher+ " ',' " +dateAdded+ " ',' " +x+ " ',' " +y+ " ',' " +z+" ')");
}
catch (Exception e) {
e.printStackTrace();
}
finally {
try {
if (rs != null) rs.close();
}
catch (SQLException e) {
e.printStackTrace();
}
try {
if (stmt != null) stmt.close();
}
catch (SQLException e) {
e.printStackTrace();
}
try {
if (conn != null) conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
System.out.println("+------------------------------------+");
System.out.println("| The Book is Added to the Inventory |");
System.out.println("+------------------------------------+\n");
}
}
}