package org.example; import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; // 按两次 Shift 打开“随处搜索”对话框并输入 `show whitespaces`, // 然后按 Enter 键。现在,您可以在代码中看到空格字符。 public class Main3 { public static void main(String[] args) throws Exception { Class.forName("com.mysql.jdbc.Driver"); String url="jdbc:mysql://127.0.0.1:3306/small?useSSL=false"; // String url="jdbc:mysql:///small"; // String url="jdbc:mysql:///small?useSSL=false"; String username="root"; String password="123456"; Connection conn =DriverManager.getConnection(url,username,password); String sql1="select *from instructor " ; Statement stmt=conn.createStatement(); ResultSet rs=stmt.executeQuery(sql1); while (rs.next()){ int id=rs.getInt(1); String name=rs.getString(2); String d_name= rs.getString(3); double money=rs.getDouble(4); System.out.println(id); System.out.println(name); System.out.println(d_name); System.out.println(money); System.out.println("---------------------"); } rs.close(); stmt.close(); conn.close(); } }
时间: 2024-02-14 07:25:21 浏览: 21
您的代码看起来没有问题。您提供的代码片中,您已经加载MySQL驱动程序并提供的URL、用户名密码成功连接到数据库然后,您执行了SELECT查询,并在控台打印了结果集中的。
请确保您的MySQL服务器正在运行,并且数据库`small`以及其中的`instructor`存在,并且包含所需的。如果数据库或表不存在您可能需要创建它,并确保表中存在以供查询。
另外,请确保您已经正确地将MySQL驱动程序JAR文件添加到项目的依赖项中并放置在类路径下。
如果您遇到任何错误或问题,请提供相关的错误消息以便我更好地帮助您。
相关问题
用java语言,在包中创建测试类FindAllUsersTest,实现读取users表中所有的数据。运行FindAllUsersTest.java程序后,控制台会打印出users表中所有的username值
假设你已经有了一个User类,该类对应着users表的结构,同时也已经配置好了JDBC连接数据库。那么你可以按照如下步骤来创建测试类FindAllUsersTest:
1. 在你的项目中新建一个包,例如com.example.test。
2. 在该包下创建一个类FindAllUsersTest,并添加如下代码:
```java
package com.example.test;
import com.example.User;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class FindAllUsersTest {
public static void main(String[] args) {
String url = "jdbc:mysql://localhost:3306/mydatabase";
String user = "root";
String password = "mypassword";
try (Connection connection = DriverManager.getConnection(url, user, password)) {
Statement statement = connection.createStatement();
ResultSet resultSet = statement.executeQuery("SELECT username FROM users");
while (resultSet.next()) {
String username = resultSet.getString("username");
System.out.println(username);
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
```
上述代码中,我们首先定义了连接数据库所需的url、user和password。然后,在try-with-resources语句块中,我们获取了数据库连接,并创建了一个Statement对象。接着,我们执行了一条SELECT语句,查询users表中的所有username值,并使用ResultSet对象遍历结果集,将每个username值输出到控制台。
3. 运行FindAllUsersTest.java程序,即可在控制台看到users表中所有的username值。
需要注意的是,上述代码中的url、user和password应该根据你的实际情况进行修改。另外,如果你的User类中已经定义了一个toString()方法,你也可以直接使用resultSet.getObject()方法获取整个User对象,并直接将User对象输出到控制台。
使用mvc模式,实现订单的增删改查,包括list.jsp.listServlet,listDao
好的,我会根据您的要求来回答问题,以下是使用MVC模式实现订单的增删改查的代码:
list.jsp:
```html
<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<title>订单列表</title>
</head>
<body>
<h1>订单列表</h1>
<table>
<tr>
<th>订单号</th>
<th>订单名称</th>
<th>订单金额</th>
<th>操作</th>
</tr>
<c:forEach items="${orders}" var="order">
<tr>
<td>${order.orderId}</td>
<td>${order.orderName}</td>
<td>${order.orderAmount}</td>
<td>
<a href="updateServlet?orderId=${order.orderId}">修改</a>
<a href="deleteServlet?orderId=${order.orderId}">删除</a>
</td>
</tr>
</c:forEach>
</table>
<a href="add.jsp">添加订单</a>
</body>
</html>
```
listServlet:
```java
package com.example.controller;
import com.example.dao.OrderDao;
import com.example.model.Order;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.util.List;
@WebServlet("/listServlet")
public class ListServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
OrderDao orderDao = new OrderDao();
List<Order> orders = orderDao.findAll();
request.setAttribute("orders", orders);
request.getRequestDispatcher("/list.jsp").forward(request, response);
}
}
```
listDao:
```java
package com.example.dao;
import com.example.model.Order;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
public class OrderDao {
private static final String URL = "jdbc:mysql://localhost:3306/order_db?useSSL=false&serverTimezone=UTC";
private static final String USER = "root";
private static final String PASSWORD = "123456";
private Connection conn = null;
private PreparedStatement pstmt = null;
private ResultSet rs = null;
public List<Order> findAll() {
List<Order> orders = new ArrayList<>();
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection(URL, USER, PASSWORD);
String sql = "SELECT * FROM orders";
pstmt = conn.prepareStatement(sql);
rs = pstmt.executeQuery();
while (rs.next()) {
Order order = new Order();
order.setOrderId(rs.getInt("orderId"));
order.setOrderName(rs.getString("orderName"));
order.setOrderAmount(rs.getDouble("orderAmount"));
orders.add(order);
}
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
close(conn, pstmt, rs);
}
return orders;
}
public void add(Order order) {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection(URL, USER, PASSWORD);
String sql = "INSERT INTO orders(orderName, orderAmount) VALUES (?, ?)";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, order.getOrderName());
pstmt.setDouble(2, order.getOrderAmount());
pstmt.executeUpdate();
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
close(conn, pstmt, rs);
}
}
public void update(Order order) {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection(URL, USER, PASSWORD);
String sql = "UPDATE orders SET orderName = ?, orderAmount = ? WHERE orderId = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setString(1, order.getOrderName());
pstmt.setDouble(2, order.getOrderAmount());
pstmt.setInt(3, order.getOrderId());
pstmt.executeUpdate();
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
close(conn, pstmt, rs);
}
}
public void delete(int orderId) {
try {
Class.forName("com.mysql.cj.jdbc.Driver");
conn = DriverManager.getConnection(URL, USER, PASSWORD);
String sql = "DELETE FROM orders WHERE orderId = ?";
pstmt = conn.prepareStatement(sql);
pstmt.setInt(1, orderId);
pstmt.executeUpdate();
} catch (ClassNotFoundException | SQLException e) {
e.printStackTrace();
} finally {
close(conn, pstmt, rs);
}
}
private void close(Connection conn, PreparedStatement pstmt, ResultSet rs) {
try {
if (rs != null) {
rs.close();
}
if (pstmt != null) {
pstmt.close();
}
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
```
以上就是使用MVC模式实现订单的增删改查的代码,希望能够帮助到您。