我正在编写一个管理产品的网络应用程序（用于学校）。设计如下：
在我用servlet检查登录后，我转发到另一个名为ManageMainPageServlet的servlet，其中doGet a）发布html，其中包含两个用于搜索产品的表单，以及b）将产品插入数据库。
填写第一个表单（搜索产品表单）后，它将传递给同一个servlet中的post方法，后者又将其重定向到SearchProduct servlet。
我在那里定义了init（）来注册所有用于连接数据库的变量（我已经测试并运行）。
在init（我知道第一次只运行一次）后，我假设代码转到doGet方法，开始管理查询。这对我不起作用，它会返回到ManageMainPageServlet。
我尝试使用dispatcher.forward，我现在写的是会发生什么，如果我尝试将其更改为response.redirect，它甚至不会进入SearchProduct中的init（）函数。
我缺少什么？
这是ManageMainPageServlet的代码：
@WebServlet(name = "ManageMainPageServlet", urlPatterns = {"/ManageMainPageServlet"})
public class ManageMainPageServlet extends HttpServlet {
/**
* Handles the HTTP
* <code>GET</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
HttpSession session = request.getSession(false);
if(session==null || (Boolean)session.getAttribute("logged") == false)
response.sendRedirect("index.html");
out.println("<!DOCTYPE html>"+
"<html>\n"+
"<head><title>Welcome to Main Page</title></head>\n"+
"<body>\n"+
"<h1> Welcome to Main Page</h1>\n"+
"<form action=\"ManageMainPageServlet\" method=\"POST\">\n"+
" Enter product name and\\or product id to search:<br>\n"+
"Product Name: <input type=\"text\" name=\"productName\" /><br>\n"+
"Product ID:<input type=\"text\" name=\"productId\" /> <br>\n"+
" <input type=\"hidden\" name=\"direction\" value=\"/SearchProduct\">\n"+
" <input type=\"submit\" />\n"+
"</form>\n"+
" <form action=\"ManageMainPageServlet\" method=\"POST\">\n"+
"Fill in the fields to enter new product into DB.\n"+
" <br>Product Name: <input type=\"text\" name=\"productName\" />\n"+
" <br>Product ID: <input type=\"text\" name=\"productId\" />\n"+
"<br>Price: <input type=\"text\" name=\"price\" />\n"+
"<br>Quantity: <input type=\"text\" name=\"productId\" />\n"+
" <br>Product Description: <br><textarea rows=\"4\" cols=\"50\" name=\"description\"></textarea>\n"+
" <input type=\"hidden\" name=\"direction\" value=\"\">\n"+
" <br> <input type=\"submit\" />\n"+
" </form>\n"+
" <form action=\"LogOutServlet\" method=\"GET\">\n"+
" <input type=\"submit\" value=\"logout\"/>\n"+
" </form>\n"+
"</body></html>");
}
/**
* Handles the HTTP
* <code>POST</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String direction = request.getParameter("direction");
//response.sendRedirect(direction);
RequestDispatcher rd = request.getRequestDispatcher(direction);
rd.forward(request, response);
}
这是SearchProduct servlet的代码：
@WebServlet(name = "SearchProduct", urlPatterns = {"/SearchProduct"})
public class SearchProduct extends HttpServlet {
private Connection con=null;
private String url=null;
private String user=null;
private String password=null;
private String odbcDriver=null;
/**
* initializes servlet with db connection and throws back error if the
* connection failed for some reason
*/
@Override
public void init(ServletConfig servletConfig) throws ServletException {
try {
this.url = servletConfig.getInitParameter("dbUrl");
this.user = servletConfig.getInitParameter("user");
this.odbcDriver = servletConfig.getInitParameter("odbcDriver");
Class.forName(odbcDriver);
} catch (Exception e) {
//decide how to handle the exception
System.out.println("Failed to load the driver");
return;
}
}
/**
* Handles the HTTP
* <code>GET</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
String productName = request.getParameter("productName");
String productID = request.getParameter("productID");
try {
try {
// Create the connection to the database
con = DriverManager.getConnection(url,user,password);
System.out.println("Made a connection to the database");
} catch (Exception e) {
System.out.println("Exception was thrown:\n");
e.printStackTrace();
}
// Get a statement object from the connection
//
Statement statement = con.createStatement();
if(productID==null);
} catch (Exception e) {
System.out.println("Exception was thrown:\n");
e.printStackTrace();
} finally {
try {
if (con != null) { con.close(); }
}catch (SQLException e) {
e.printStackTrace();
}
}
}
}