在 JSP 中将 JavaBean 放入 HttpSession [英] Putting a JavaBean into a HttpSession in JSP
问题描述
我试图做一个关于调查的简单"应用程序.您有一些选项(复选框)，然后结果(投票)显示在其他页面中.
I was trying to do a "simple" application about a survey. Where you have some options (checkboxes) and then the results (votes) are shown in other page.
我有这个类，我可以一直保存结果(我想使用 HttpSession 更新这个类).我用的是HashMap这个类，但是我改了，我觉得没关系:
I have this class where I can keep the results all time (I want to update this class, using HttpSession). I was using the class HashMap, but I changed, I think it doesn't matter:
package beans;
import java.util.ArrayList;
import java.util.List;
public class SurveyBean {
private List<String> keys;
private List<String> values;
public SurveyBean() {
keys = new ArrayList<String>(); //keys: {"Cat", "Dog", "Other animal"}
values = new ArrayList<String>(); //Values: {"12","5","4"}
// By example, a value of 12 means, 12 people like cats.
keys.add("Cat");
keys.add("Dog");
keys.add("Bird");
// Don't ask me why did I use Strings instead of Integers.
values.add("0"); // Zero votes
values.add("0");
values.add("0");
}
// add one vote to the list of values
public void addVote( String key, int value ) {
int index = keys.indexOf(key);
int newValue = Integer.parseInt(values.get(index)) + value;
values.set(index, "" + newValue);
}
/********* Get and set methods *********/
现在，这是主窗体 (jsp)，它尝试将 JavaBean 放入会话中:注意:我正在使用旧的 JSP sintaxis，因为我还在学习中.
Now, this is the main form (jsp), which tries to put a JavaBean into the session: Note: I'm using old sintaxis of JSP, because I'm still learning.
<%@page contentType="text/html" session="true" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<!-- Create the JavaBean "SurveyBean" (Scope: session) -->
<jsp:useBean id="survey" class="beans.SurveyBean" scope="session" />
What's your favorite animal ?
<form action="page2.jsp" method="POST">
<%
java.util.List<String> list = survey.getKeys();
/* It prints:
* What's your favorite animal? (Bird,Dog,Cat, etc.)
*/
for( int i = 0; i < list.size(); i++ ) {
out.println("<input type=\"radio\" name=\"name\" value=\"" + list.get(i) +"\">" + list.get(i) + "<br>");
}
%>
<input type="submit" value="Send" />
</form>
</body>
这是结果页面:
<%@page import="beans.SurveyBean, java.util.*"%>
<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>JSP Page</title>
</head>
<body>
<%
// getting the checKbox selected
String name = request.getParameter("name");
// Trying to get the object survey from the session
HttpSession ses = request.getSession(false);
SurveyBean sv = (SurveyBean) request.getAttribute("survey");
// Add one vote to the list of values
List<String> keys = sv.getKeys();
List<String> values = sv.getValues();
// I can't use the objects "Keys" and "values", because they are marked as Null.
// Why they are Null !!!! ???
%>
</body>
这里的问题是我不能使用对象SurveyBean.我不确定第一页(表单)是否正确初始化了 bean.而且我无法从会话中获取对象.
注意:对不起，我的英语真的很差.
The problem here is I can't use the object SurveyBean. I'm not sure if the first page (form) initializes the bean correctly. And I can't get the object from the session.
Note: Sorry, my English is really bad.
推荐答案
现在我已经解决了这个问题.在第一个 jsp 中，它将对象调查放在会话中.我添加这一行:
Now I've solved the problem. In the first jsp, which puts the object survey in the session. I add this line:
request.setAttribute("survey2",survey2);
在接收对象的第二页中，我添加了另一行:
And in the second page, which receives the object, I add this other line:
<%@page contentType="text/html" pageEncoding="UTF-8" session="true"%>
我认为有必要在指令@page 中添加属性session".
I suposse it was neccesary to add the attribute "session" in the directive @page.
实际上，这不是解决方案.我认为它有效，因为我已将代码放入 Servlet 中，如下所示:
In reality, that's not the solution. I think it works because I've put the code into a Servlet, like this:
PrintWriter out = response.getWriter();
try {
//Getting the parameter and the object survey
String name = request.getParameter("name");
HttpSession ses = request.getSession(false);
SurveyBean survey = (SurveyBean) ses.getAttribute("survey");
// Adding one vote
survey.addVote(name,1);
// Forwarding
ses.setAttribute("survey", survey);
RequestDispatcher rd = request.getRequestDispatcher("/page2.jsp");
rd.forward(request, response);
} finally {
out.close();
}
这篇关于在 JSP 中将 JavaBean 放入 HttpSession的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
