题目：
编写一个应用程序，输入用户名和密码，访问test数据库中t_login表（字段包括id、username、password），验证登录是否成功。在上一题基础上，当登录成功后，将t_user表（id、name、sex、birthday）的信息进行显示（要求使用DB.java完成登录和获取t_user表中数据的操作），最后再对t_user表进行一条记录的添加操作。
代码：
DB类：
1 package 第15周作业;
2
3 import java.sql.Connection;
4 import java.sql.DriverManager;
5 import java.sql.PreparedStatement;
6 import java.sql.ResultSet;
7 import java.sql.SQLException;
8
9 import com.mysql.cj.xdevapi.Statement;
10 /**
11 * 封装连接数据库以及增删改查操作。
12 *
13 */
14 public class DB {
15 private static DB db;
16 private Connection con;
17 private PreparedStatement ps;
18 private ResultSet rs;
19 static {
20 try {
21 Class.forName("com.mysql.cj.jdbc.Driver");
22 } catch (ClassNotFoundException e) {
23 e.printStackTrace();
24 }
25 }
26
27 public static DB getInstance() {
28 if (db == null) {
29 db = new DB();
30 }
31 return db;
32 }
33
34 private DB() {// 通过构造方法创建数据库链接
35 try {
36 con = DriverManager.getConnection("jdbc:mysql://localhost:3306/java?serverTimezone=UTC", "root", "");
37 } catch (SQLException e) {
38 e.printStackTrace();
39 }
40 }
41
42 public ResultSet DBQuery(String sql, Object[] field) {
43 try {
44 ps = con.prepareStatement(sql);
45 if (field.length > 0) {
46 for (int i = 0; i < field.length; i++) {
47 ps.setObject(i + 1, field[i]);
48 }
49 }
50 rs = ps.executeQuery();
51 } catch (SQLException e) {
52 e.printStackTrace();
53 }
54 return rs;
55 }
56
57 public ResultSet DBQuery(String sql) {
58 try {
59 ps = con.prepareStatement(sql);
60 rs = ps.executeQuery();
61 } catch (SQLException e) {
62 e.printStackTrace();
63 }
64 return rs;
65 }
66
67 public int DBModify(String sql, Object[] field) {
68 int n = 0;
69 try {
70 ps = con.prepareStatement(sql);
71 if (field.length > 0)
72 for (int i = 0; i < field.length; i++) {
73 ps.setObject(i + 1, field[i]);
74 }
75 n = ps.executeUpdate();
76 } catch (SQLException e) {
77 e.printStackTrace();
78 }
79 return n;
80 }
81
82 public void close() {
83 try {
84 if (rs != null) {
85 rs.close();
86 }
87 ps.close();
88 con.close();
89 } catch (SQLException e) {
90 e.printStackTrace();
91 }
92 }
93 }
测试类：
1 package 第15周作业;
2
3 import java.sql.ResultSet;
4 import java.sql.SQLException;
5 import java.util.Scanner;
6
7 import javax.swing.plaf.synth.SynthStyle;
8 import javax.xml.crypto.Data;
9
10 /**
11 *
12 *
13 * 调用数据库进行增删改查
14 *
15 */
16 public class Test {
17
18 public static void main(String[] args) {
19 DB db = DB.getInstance();
20 boolean flag = false;
21 Scanner scan = new Scanner(System.in);
22 String[] user = new String[2];
23 user[0] = scan.next();
24 user[1] = scan.next();
25 String sql = "SELECT * FROM t_login where username = ? AND password=?";
26 ResultSet rs = db.DBQuery(sql, user);
27 try {
28 if (rs.next()) {
29 System.out.println("登录成功！");
30 flag = true;
31 }
32 } catch (SQLException e) {
33 e.printStackTrace();
34 }
35 if (flag) {
36 sql = "select id,name,CASE sex WHEN 0 THEN '男' ELSE '女' END as sex,birthday from t_user";
37 rs = db.DBQuery(sql);
38 try {
39 while (rs.next()) {
40 System.out.print(rs.getInt(1));
41 System.out.print(" ");
42 System.out.print(rs.getString(2));
43 System.out.print(" ");
44 System.out.print(rs.getString(3));
45 System.out.print(" ");
46 System.out.println(rs.getString(4));
47 }
48 } catch (SQLException e) {
49 e.printStackTrace();
50 }
51 String name = "a";
52 int sex = 0;
53 String date = "1998-01-01";
54 sql = "insert into t_user (name,sex,birthday)values(?,?,?)";
55 if (db.DBModify(sql, new Object[] { name, sex, date }) > 0) {
56 System.out.println("更新成功");
57 } else {
58 System.out.println("数据未更改");
59 }
60 } else {
61 System.out.println("账号或密码错误");
62 }
63
64 }
65
66 }
来源：https://www.cnblogs.com/laxla/p/12040950.html