我有一个模型，其中有一个数组列表。我还有一个需要从模型中提取的 servlet。最后，JSP 需要获取从 servlet( Controller )检索的信息并生成选择列表的选项。我不明白为什么这根本不起作用。我刚刚进入 jsp，所以任何帮助将不胜感激。
我有下面 3 页和堆栈跟踪。
所建议的任何有助于 future 发展的更改也会有所帮助。我非常开放，并且希望以正确的方式做到这一点。
模型(有数组列表)
package edu.witc.Assignment03.model;
import java.util.ArrayList;
import java.util.List;
public class States {
private List<String> states = new ArrayList<>();{
states.add("Alabama");
states.add("Alaska");
states.add("Arizona");
states.add("Arkansas");
states.add("California");
states.add("Colorado");
states.add("Connecticut");
states.add("Delaware");
states.add("Florida");
states.add("Georgia");
states.add("Hawaii");
states.add("Idaho");
states.add("Illinois");
states.add("Indiana");
states.add("Iowa");
states.add("Kansas");
states.add("Kentucky");
states.add("Louisiana");
states.add("Maine");
states.add("Maryland");
states.add("Massachusetts");
states.add("Michigan");
states.add("Minnesota");
states.add("Mississippi");
states.add("Missouri");
states.add("Montana");
states.add("Nebraska");
states.add("Nevada");
states.add("New Hampshire");
states.add("New Jersey");
states.add("New Mexico");
states.add("New York");
states.add("North Carolina");
states.add("North Dakota");
states.add("Ohio");
states.add("Oklahoma");
states.add("Oregon");
states.add("Pennsylvania");
states.add("Rhode Island");
states.add("South Carolina");
states.add("South Dakota");
states.add("Tennessee");
states.add("Texas");
states.add("Utah");
states.add("Vermont");
states.add("Virginia");
states.add("Washington");
states.add("West Virginia");
states.add("Wisconsin");
states.add("Wyoming");
}
public List<String> getStates(){
return this.states;
}
}
Controller (Servlet)
package edu.witc.Assignment03.controller;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.*;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
//import javax.servlet.annotation.WebServlet;
//import javax.servlet.http.HttpServlet;
//import javax.servlet.http.HttpServletRequest;
//import javax.servlet.http.HttpServletResponse;
import edu.witc.Assignment03.model.Customer;
import edu.witc.Assignment03.model.Phone;
import edu.witc.Assignment03.model.States;
/*
* Not thread-safe. For illustration purpose only
*/
@WebServlet(name = "CustomerServlet", urlPatterns = {
"/customerManagement"})
public class CustomerServlet extends HttpServlet {
private static final long serialVersionUID = -20L;
private edu.witc.Assignment03.model.States states = new States();
private List<edu.witc.Assignment03.model.Customer> customers = new ArrayList<Customer>();
private void addCustomer(HttpServletResponse response, HttpServletRequest request)//redirect to index
throws IOException, ServletException {
String url = "/customerManagement.jsp";
request.setAttribute("customers", customers);
request.getRequestDispatcher(url).forward(request,response);
}
private void editCustomer(HttpServletResponse response, HttpServletRequest request)//redirect to index
throws IOException, ServletException {
String url = "/customerManagement.jsp";
request.setAttribute("customers", customers);
request.getRequestDispatcher(url).forward(request,response);
}
private void sendCustomerList(HttpServletResponse response, HttpServletRequest request)//redirect to index
throws IOException, ServletException {
String url = "/index.jsp";
request.setAttribute("customers", customers);
request.getRequestDispatcher(url).forward(request,response);
}
private Customer getCustomer(int customerId) {
for (Customer customer : customers) {
if (customer.getCustomerId() == customerId) {
return customer;
}
}
return null;
}
private void sendEditCustomerForm(HttpServletRequest request,
HttpServletResponse response) throws IOException, ServletException {
String url = "/customerManagement.jsp";
request.setAttribute("customers", customers);
request.getRequestDispatcher(url).forward(request,response);
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String uri = request.getRequestURI();
if (uri.endsWith("/customer")) {
sendCustomerList(response, request);
} else if (uri.endsWith("/editCustomer")) {
sendEditCustomerForm(request, response);
}
request.setAttribute("states", states);
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// update customer
int customerId = 0;
try {
customerId =
Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e) {
}
Customer customer = getCustomer(customerId);
if (customer != null) {
customer.setFirstName(request.getParameter("firstName"));
customer.setLastName(request.getParameter("lastName"));
customer.setEmail(request.getParameter("email"));
customer.setPhone(request.getParameter("phone"));
customer.setAddress(request.getParameter("address"));
customer.setCity(request.getParameter("city"));
customer.setZip(request.getParameter("zip"));
}
addCustomer(response, request);
}
}
JSP页面(带有选择/选项列表的表单)
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.ArrayList" %>
<!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=ISO-8859-1">
<title>Customer Management</title>
</head>
<body>
<form action="/CustomerServlet" method="post">
First Name:<br>
<input type="text" name="firstName"/><br>
Last Name:<br>
<input type="text" name="lastName"/><br>
Email:<br>
<input type="text" name="email"/><br>
Phone:<br>
<input type="text" name="phone"/><br>
Phone Type:<br>
Street Address:<br>
<input type="text" name="streetAddress"/><br>
Apartment Number:<br>
<input type="text" name="apartmentNumber"/><br>
City:<br>
<input type="text" name="city"/><br>
State:<br>
<select>
<%
edu.witc.Assignment03.model.States states = request.getAttribute("states");
if(states!=null){
for (String state : states.getStates()) {
out.println("<option>"+state+"</option>");
}
}else{
System.out.print("states is null");
}
%>
</select><br>
<input type="submit" value="submit">
</form>
</body>
</html>
堆栈跟踪
Mar 30, 2014 8:17:13 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/Justin_EJ_Assignment03_15400579] threw exception [Unable to compile class for JSP:
An error occurred at line: 33 in the jsp file: /customerManagement.jsp
Type mismatch: cannot convert from Object to States
30: State:<br>
31: <select>
32: <%
33: edu.witc.Assignment03.model.States states = request.getAttribute("states");
34: if(states!=null){
35: for (String state : states.getStates()) {
36: out.println("<option>"+state+"</option>");
Stacktrace:] with root cause
org.apache.jasper.JasperException: Unable to compile class for JSP:
An error occurred at line: 33 in the jsp file: /customerManagement.jsp
Type mismatch: cannot convert from Object to States
30: State:<br>
31: <select>
32: <%
33: edu.witc.Assignment03.model.States states = request.getAttribute("states");
34: if(states!=null){
35: for (String state : states.getStates()) {
36: out.println("<option>"+state+"</option>");
Stacktrace:
at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:103)
at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:366)
at org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:468)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:378)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:353)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:340)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:657)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:357)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:241)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:170)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:98)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1040)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:607)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:313)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)
最佳答案
getAttribute()返回 Object 所以你需要添加强制转换，最好在这里使用 JSTL
<c:forEach var="state" items="states">
<option>
<c:out value="${person.name}" />
</option>
</c:forEach>
关于java - 从模型获取信息到 Servlet 再到 JSP 选项列表，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/22751696/