从JAVA到JDBC的感受
1.在JDBC中excuteUpdate()与executeUpdate(sql)的区别：
如果执行的sql语句中有变量，则应选用不带参数的excute语句，若sql语句不带变量，则应选用不带参数的语句。
2.带变量的sql语句可以有两种方式表示（以insert语句为例）：
1⃣️ PreparedStatment stmt = new PreparedStatment()
sql = "insert into tableName (a,b,c,d,e) values(?,?,?,?,?)";
stmt.set[String](1,a);
stmt.set[String](2,b);
stmt.set[String](3,c);
stmt.set[String](4,d);
stmt.set[String](5,e);
2⃣️ Statementst =conn.createStatement();
String sql = "insert into tableName (a,b) values ('"+a+"','"+b+"')";
3.可以定义配置文件以工厂形式来存放数据库连接的数据；
4.可以将数据库中的列封装到对象<List>中;
5.初步代码如下：
MysqlCon.java
import java.io.FileReader;
import java.io.Reader;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
import com.mysql.jdbc.PreparedStatement;
public class MysqlCon {
private static String driver;
private static String url;
private static String username;
private static String password;
static{
Properties prop = new Properties();
Reader in;
try{
in = new FileReader("src//config.properties");
prop.load(in);
}catch(Exception e){
e.printStackTrace();
}
driver = prop.getProperty("driver");
url = prop.getProperty("url");
username = prop.getProperty("username");
password = prop.getProperty("password");
try{
Class.forName(driver);
}catch(ClassNotFoundException e){
System.out.println(e);
}
}
public static String Mysqllogin_compare(String username_cp){
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql = "select * from user where user.name='"+username_cp+"'";
ResultSet rs = st.executeQuery(sql);
String password_cp = null;
if(rs.next()){
password_cp = rs.getString(5);
}
rs.close();
conn.close();
return password_cp;
}
}catch (SQLException e) {
// e.printStackTrace();
}
return null;
}
public void Mysql_save(String name, String num, String sex, int age){
String name_save = name;
String num_save = num;
String sex_save = sex;
int age_save = age;
String password_save = num;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
String sql = "insert into user (name,num,age,sex,password) values(?,?,?,?,?)";
String sql1 = "insert into base (ANAME,NUM,ACCOUNT) values(?,?,?)";
PreparedStatement st= (PreparedStatement) conn.prepareStatement(sql);
st.setString(1, name_save);
st.setString(2, num_save);
st.setInt(3, age_save);
st.setString(4, sex_save);
st.setString(5, password_save);
st.executeUpdate();
PreparedStatement st1= (PreparedStatement) conn.prepareStatement(sql1);
st1.setString(1, name_save);
st1.setString(2, num_save);
st1.setInt(3, 0);
st1.executeUpdate();
System.out.println("注册成功");
} conn.close();
}catch(Exception e){
e.printStackTrace();
}
}
public static void save_money(String username_cp,int account_cp){
String name = username_cp;
int account = 0;
int account_inc = account_cp;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql1 = "select * from base where base.ANAME='"+name+"'";
ResultSet rst = st.executeQuery(sql1);
if(rst.next()){
account = rst.getInt(3);
// System.out.println(account);
}
account = account + account_inc;
String sql = "update base set base.ACCOUNT='"+account+"' where base.ANAME='"+name+"'";
st.executeUpdate(sql);
System.out.println("存款成功");
rst.close();
conn.close();
}
}catch (SQLException e) {
// e.printStackTrace();
}
}
public static void out_money(String username_cp,int account_cp){
String name = username_cp;
int account = 0;
int out_account = account_cp;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql1 = "select * from base where base.ANAME='"+name+"'";
ResultSet rst = st.executeQuery(sql1);
if(rst.next()){
account = rst.getInt(3);
// System.out.println(account);
}
if((account - out_account) >= 0){
account = account - out_account;
String sql = "update base set base.ACCOUNT='"+account+"' where base.ANAME='"+name+"'";
st.executeUpdate(sql);
System.out.printf("取款成功，您的账户余额为%d",account);
rst.close();
conn.close();
}
}
else{
System.out.println("您的余额不足，别逗了!");
}
}catch (SQLException e) {
// e.printStackTrace();
}
}
public static void pass_money(String username_cp, String num_cp, int account_cp) {
String name = username_cp;
String num = num_cp;
int out_account = account_cp;
int left_account = 0;
int inc_account = 0;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql1 = "select * from base where base.ANAME='"+name+"'";
ResultSet rst = st.executeQuery(sql1);
if(rst.next()){
left_account = rst.getInt(3);
// System.out.println(account);
}
if((left_account - out_account) >= 0){
left_account = left_account - out_account;
String sql = "update base set base.ACCOUNT='"+left_account+"' where base.ANAME='"+name+"'";
st.executeUpdate(sql);
String sq3 = "select * from base where base.NUM='"+num+"'";
ResultSet rst2 = st.executeQuery(sq3);
if(rst2.next()){
inc_account = rst2.getInt(3);
}
inc_account = inc_account + out_account;
String sq2 = "update base set base.ACCOUNT='"+inc_account+"' where base.NUM='"+num+"'";
st.executeUpdate(sq2);
System.out.printf("转账成功，您的账户余额为%d\n",left_account);
rst2.close();
rst.close();
conn.close();
}
else{
System.out.println("您的余额不足，别逗了!");
}
}
}catch (SQLException e) {
// e.printStackTrace();
}
}
public static void lord_money(String username_cp,int account_cp){
String name = username_cp;
int account = 0;
int account_inc = account_cp;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql1 = "select * from base where base.ANAME='"+name+"'";
ResultSet rst = st.executeQuery(sql1);
if(rst.next()){
account = rst.getInt(3);
// System.out.println(account);
}
account = account + account_inc;
String sql = "update base set base.ACCOUNT='"+account+"' where base.ANAME='"+name+"'";
st.executeUpdate(sql);
System.out.println("贷款成功");
// System.out.println("您的还款日期为");
rst.close();
conn.close();
}
}catch (SQLException e) {
// e.printStackTrace();
}
}
public static void show_money(String username_cp){
String name = username_cp;
int account = 0;
try {
Connection conn = DriverManager.getConnection(url, username, password);
if(!conn.isClosed()){
System.out.println("Succeeded connecting to the Database!");
Statement st = conn.createStatement();
String sql1 = "select * from base where base.ANAME='"+name+"'";
ResultSet rst = st.executeQuery(sql1);
if(rst.next()){
account = rst.getInt(3);
// System.out.println(account);
}
System.out.println(account);
rst.close();
conn.close();
}
}catch (SQLException e) {
// e.printStackTrace();
}
}
}
import java.util.Scanner;
public class ShowWindow {
private static String name;
private static int in_account;
private static int out_account;
private static int pass_account;
private static String pass_num;
private static int lord_account;
static MysqlCon msq = new MysqlCon();
public static void show_menu( ){
System.out.println(".......1.存款.......\n");
System.out.println(".......2.取款.......\n");
System.out.println(".......3.转账.......\n");
System.out.println(".......4.贷款.......\n");
System.out.println(".......5.退出.......\n");
System.out.println(".......6.显示余额.......\n");
}
public static void main(String[] args){
System.out.println("请登陆：新用户请输入1创建账户，老用户请输入2登陆");
Scanner sc = new Scanner(System.in);
int choice = sc.nextInt();
if(choice == 2){
System.out.println("请输入姓名");
name = sc.next();
System.out.println("请输入您的密码，您只有三次机会去输入正确的密码\n，如果超过三次，"
+ "处于对您财产安全的考虑，您的账户将会被"+ "冻结一小时，请谅解");
int count = 1;
while(count <= 3)
{
String password = sc.next();
if(password.equals(MysqlCon.Mysqllogin_compare(name))){
break;
}
else{
System.out.println("\n请输入正确的密码，您还有两次机会");
count++;
}
}
if(count > 3)
choice = 2;
}
else if(choice == 1){
System.out.println("请输入您的姓名:");
String name = sc.next();
System.out.println("请输入您的学号:");
String num = sc.next();
System.out.println("请输入您的性别:");
String sex = sc.next();
System.out.println("请输入您的年龄:");
int age = sc.nextInt();
System.out.println("您的密码将自动生成为您的学号:\n");
msq.Mysql_save(name, num, sex, age);
System.out.println("创建成功，即将退回到登陆界面\n");
}
System.out.println("登陆成功\n");
System.out.println("请选择您要进行的操作\n");
int num = 1;
while(num != 0){
show_menu();
num = sc.nextInt();
switch(num){
case 1:
System.out.println("你选择的是存款\n");
System.out.println("请输入您要存入的数额：");
in_account = sc.nextInt();
MysqlCon.save_money(name,in_account);
break;
case 2:
System.out.println("你选择的是取款\n");
System.out.println("请输入您要取出的数额:");
out_account = sc.nextInt();
MysqlCon.out_money(name,out_account);
break;
case 3:
System.out.println("你选择的是转账\n");
int i = 1;
while(i == 1){
System.out.println("请输入您要转入的账号:");
pass_num = sc.next();
System.out.println("请输入转账金额");
pass_account = sc.nextInt();
MysqlCon.pass_money(name,pass_num,pass_account);
break;
}
break;
case 4:
System.out.println("你选择的是贷款\n");
System.out.println("请输入您要贷款的金额");
lord_account = sc.nextInt();
MysqlCon.lord_money(name,lord_account);
break;
case 5:
System.out.println("你选择的是退出\n");
num = 0;
break;
case 6:
System.out.println("您选择的是显示余额\n");
MysqlCon.show_money(name);
}
}
sc.close();
}
}
配置文件
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