请帮我解释以下代码:@WebServlet("/demo2") public class SessionDemo2 extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { HttpSession session = request.getSession(); System.out.println(session); Object username = session.getAttribute("username"); System.out.println(username); } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request, response); } }
时间: 2024-04-26 14:26:35 浏览: 33
这段代码是一个使用Java Servlet技术实现的Servlet类,它的URL映射路径为"/demo2"。当客户端向服务器发送一个GET请求时,Servlet会调用doGet()方法来响应请求,当客户端向服务器发送一个POST请求时,Servlet会调用doPost()方法来响应请求。在这个Servlet中,doGet()方法中获取了一个HttpSession对象,并通过getAttribute()方法获取了这个Session中名为"username"的属性值,最后将其打印到控制台上。如果这个属性不存在,它将打印null。这段代码可以用于演示如何在Java Servlet中使用Session对象来存储和获取用户信息。
相关问题
@WebServlet(name = "deleteServlet", value = "/deleteServlet") public class deleteServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } @Override protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doGet(request,response); } }在这个页面填好
这个 Servlet 是一个空实现,需要根据具体需求进行修改。以下是一个简单的删除操作的示例:
```java
@WebServlet(name = "deleteServlet", value = "/deleteServlet")
public class deleteServlet extends HttpServlet {
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String id = request.getParameter("id");
// 根据具体需求进行删除操作,以下是一个示例代码
Connection conn = null;
PreparedStatement ps = null;
try {
conn = DBUtil.getConnection();
String sql = "DELETE FROM user WHERE id = ?";
ps = conn.prepareStatement(sql);
ps.setString(1, id);
ps.executeUpdate();
response.sendRedirect("userList.jsp");
} catch (SQLException e) {
e.printStackTrace();
} finally {
DBUtil.close(conn, ps, null);
}
}
}
```
该 Servlet 接收一个 POST 请求,从请求参数中获取一个 `id` 值,然后连接数据库,执行 SQL 语句删除对应的行,并重定向到用户列表页。需要注意的是,这里使用了一个 DBUtil 类来获取数据库连接和关闭资源,可以根据自己的情况进行修改。另外,需要将 SQL 语句中的 `user` 替换成实际的表名。
@WebServlet("/*") public class StartServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { RequestDispatcher dispatcher = req.getRequestDispatcher("/main.html"); dispatcher.forward(req, resp); } } 这个servlet执行后,为什么显示的main.html没有css格式,但是我在本地打开main.html文件的时候它的静态页面css是正常加载的
这可能是因为在servlet中将请求转发到main.html时,路径没有正确处理。在servlet中,请求转发的路径是相对于servlet上下文的。所以,如果你在main.html中使用的是相对路径引用CSS文件,那么在servlet中请求转发后,相对路径就会改变,导致CSS文件无法加载。
你可以尝试在main.html中使用绝对路径来引用CSS文件,或者在servlet中使用绝对路径来转发请求。例如:
```java
@WebServlet("/*")
public class StartServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
RequestDispatcher dispatcher = req.getRequestDispatcher("/WEB-INF/main.html");
dispatcher.forward(req, resp);
}
}
```
在这个例子中,我们将请求转发到了WEB-INF文件夹下的main.html文件,这样就可以使用绝对路径来引用CSS文件了。
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谅解一下这段代码:6.BuyPhoneServlet: package Session01; 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.io.PrintWriter; import java.util.ArrayList; @WebServlet("/buyPhoneServlet") public class BuyPhoneServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.setContentType("text/html;charset=utf-8"); PrintWriter out=resp.getWriter(); String idstr=req.getParameter("id"); int id=Integer.parseInt(idstr); ArrayList ckDB= PhoneDb.getAll(); Phone ck=ckDB.get(id-1); out.println("您购买的"+ck.getName()+"手机下单成功。"); out.println("继续选购"); } }
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大致讲解一下这段代码:ListPhoneServlet: package Session01; 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.io.PrintWriter; import java.util.ArrayList; @WebServlet("/listPhones") public class ListPhoneServlet extends HttpServlet { @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { resp.setContentType("text/html;charset=utf-8"); PrintWriter out = resp.getWriter(); out.println("目前可供选择的手机如下:"); ArrayList allPhones = PhoneDb.getAll(); if (allPhones != null && allPhones.size() > 0) { for (int i = 0; i < allPhones.size(); i++) { Phone ck = allPhones.get(i); out.println("手机名:"+ck.getName()+" 价格:"+ck.getPrice()+" 立即购买 "); out.println("加入购物车
"); } } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { } }
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