得到了一个给我带来问题的家庭作业......它修改了一个带有两个页面和一个 bean 的 JSF 项目，通过添加另外两个页面和一个控制器 servlet 和另一个 bean 来适应 MVC2 两个附加页面。新的主页转发到第二个新页面或旧的第一页。我的问题是 response.getParameter() 总是导致 null。
<%@page session="false" import="java.util.Iterator"%>
<%@taglib prefix="f" uri="http://java.sun.com/jsf/core"%>
<%@taglib prefix="h" uri="http://java.sun.com/jsf/html"%>
<jsp:useBean id="status" scope="request" class="JSFRegistration.Status" />
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"
"http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"/>
<title>JSP Page</title>
</head>
<body>
<% if (status!=null && !status.isSuccessful()){%>
<font color="red">Processing errors:
<ul><%Iterator errors=status.getExceptions();
while (errors.hasNext()){
Exception e = (Exception) errors.next();%>
<li><%= e.getMessage()%><%}%></ul></font><%}%>
<form action="LoginServlet" method="POST">
<% String username = request.getParameter("username");
if (username==null) username="";%>
<input type="text" name="usernameTF" value="<%=username%>" />
<% String password = request.getParameter("password");
if (password==null) password="";%>
<input type="password" name="passwordTF" value="<%=password%>" />
<input type="submit" value="Login" />
</form>
</body>
</html>
这基本上是我们书中的直接副本，但是我需要新主页的字段。与控制器 servlet 相同，直接复制除了只包含我需要的字段。
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
RequestDispatcher view = null;
Status status = new Status();
request.setAttribute("status", status);
String username = request.getParameter("username");
String password = request.getParameter("password");
if (username==null || username.length()==0)
status.addException(new Exception("Please enter username"));
if (password==null)
status.addException(new Exception("Please enter password"));
if (!status.isSuccessful()){
view = request.getRequestDispatcher("Login.jsp");
//view.forward(request, response);
}
else
try{
request.setAttribute("username", username);
request.setAttribute("password", password);
view = request.getRequestDispatcher("Registration.jsp");
} catch (Exception e) {
status.addException(new Exception("Error"));
view = request.getRequestDispatcher("Login.jsp");
}
view.forward(request, response);
}
和 Status 类，同样是本书的直接副本。
public class Status {
private ArrayList exceptions;
public Status(){
exceptions = new ArrayList();
}
public void addException(Exception exception) {
exceptions.add(exception);
}
public boolean isSuccessful(){
return (exceptions.isEmpty());
}
public Iterator getExceptions(){
return exceptions.iterator();
}
无论在两个框中键入什么，单步调试都会显示未传递给参数的值。如果两个字段都有文本，如果只有一个有文本并且两个字段都为空，我会在屏幕上方打印创建的异常。