我有一个简单的 JSP 项目，其中有 3 个类、 Controller 和 DAO 我可以登录，但是当我单击按钮时，我无法从表单中获取参数。
让我展示一下代码，也许你会明白:
package school.controller;
import java.io.IOException;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import school.dao.StudentDAO;
import school.model.Student;
public class StudentController extends HttpServlet {
private static final long serialVersionUID = 1L;
private static String UPDATE = "/student.jsp";
private static String VIEW_COURSES = "CourseController";
private static String VIEW_GRADES = "GradeController";
private StudentDAO dao;
public StudentController() {
dao = new StudentDAO();
}
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
String forward = "";
String action = request.getParameter("name");
if (action.equalsIgnoreCase("update")) {
forward = UPDATE;
Student student = (Student) request.getAttribute("student");
request.setAttribute("student", student);
} else if (action.equalsIgnoreCase("viewgrades")) {
forward = VIEW_GRADES;
Student student = (Student) request.getAttribute("student");
request.setAttribute("student", student);
} else if (action.equalsIgnoreCase("viewcourses")) {
forward = VIEW_COURSES;
Student student = (Student) request.getAttribute("student");
request.setAttribute("student", student);
}
RequestDispatcher view = request.getRequestDispatcher(forward);
view.forward(request, response);
}
protected void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
这是 WEB.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
<display-name>School_JSP</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<description></description>
<display-name>CourseController</display-name>
<servlet-name>CourseController</servlet-name>
<servlet-class>school.controller.CourseController</servlet-class>
</servlet>
<servlet>
<description></description>
<display-name>StudentController</display-name>
<servlet-name>StudentController</servlet-name>
<servlet-class>school.controller.StudentController</servlet-class>
</servlet>
<servlet>
<description></description>
<display-name>LoginServlet</display-name>
<servlet-name>LoginServlet</servlet-name>
<servlet-class>school.controller.LoginServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>StudentController</servlet-name>
<url-pattern>/StudentController</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>CourseController</servlet-name>
<url-pattern>/CourseController</url-pattern>
</servlet-mapping>
</web-app>
和 mainPage.jsp
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core"%>
<!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>Main Page</title>
</head>
<body>
<h3>
Welcome,
<c:out value="${student.firstName}" />
</br>
<h1>My Personal Information</h1>
<center>
<form method="POST" action='StudentController' name="viewgrades">
<input type="submit" value="View My Grades" />
</form>
<form method="POST" action='StudentController' name="viewcourses">
<input type="submit" id="hidden" value="View My Courses" />
</form>
<form method="POST" action='StudentController' name="update">
<input type="submit" id="hidden" value="Update Personal Information" />
</form>
</center>
</h3>
</body>
</html>
最佳答案
您混淆了属性和参数。
参数是浏览器发送的字符串值。可使用 getParameterXxx() 系列方法来访问它们。
属性是您可以添加到请求(或 session 或 servlet 上下文)或任何类型的数据，以便稍后获取它们。您通常会在 servlet 中向请求添加一个属性(例如，有关登录用户的信息)，以便在 JSP 中取回该属性并显示该信息。
在您的代码中，您获取参数的唯一位置已被注释掉。您正在尝试获取一个名为“hidden”的参数，尽管没有一个表单具有包含该名称的输入字段。它是浏览器提交的输入字段的 name 属性，而不是其 id 属性。
此外，对于获取或读取内容的操作，您应该使用 GET 而不是 POST。
关于java - JSP获取参数，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/16257420/