从豆类型的数组列表填充在JSP中的下拉列表 [英] Populating a drop down list in JSP from a Array List of Bean type
问题描述
在我的Java EE项目，我有以下的Servlet：
In my Java EE project I have the following Servlet:
import java.io.IOException;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ArrayList;
import javax.naming.InitialContext;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.sql.DataSource;
/**
* Servlet implementation class TitlePopulatorServlet
*/
@WebServlet("/TitlePopulatorServlet")
public class TitlePopulatorServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* @see HttpServlet#HttpServlet()
*/
public TitlePopulatorServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
System.out.println("Inside doGet()!");
ArrayList<BeanTitle> bt=new ArrayList<BeanTitle>();
java.io.PrintWriter out = response.getWriter();
response.setContentType("text/html");
Connection conn=null;
try {
/* get the DataSource from using the JNDI name */
Class.forName("com.mysql.jdbc.Driver");
InitialContext ctx = new InitialContext();
DataSource ds = (DataSource)ctx.lookup("java:comp/env/jdbc/Test");
//Create connection and then continue as usual other JDBC calls
conn=ds.getConnection();
System.out.println("\nConnection Successful in TitlePopulatorServlet !");
Statement s= conn.createStatement();
ResultSet rs=s.executeQuery("SELECT * FROM story");
while (rs.next() )
{
BeanTitle b = new BeanTitle();
b.setBtitle(rs.getString(1));
bt.add(b);
}
} catch (Exception e){
out.println("Failed!"+ e);
}
request.setAttribute("bt", bt);
request.getRequestDispatcher("/StoryTitlePage.jsp").forward(request,response);
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
}
}
的BeanTitle如下：
The BeanTitle is as follows:
public class BeanTitle
{
private String btitle;
public String getBtitle() {
return btitle;
}
public void setBtitle(String btitle) {
this.btitle = btitle;
}
}
和JSP页面（StoryTitlePage.jsp）如下：
And the JSP page ("StoryTitlePage.jsp") is as follows:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<jsp:useBean id="storylist" class="serv.TitlePopulatorServlet" scope="request" />
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Story Title Page</title>
</head>
<body>
<form action="/ReportData/DisplayReport" method="post" >
Please select an element:
<select id="selectedRecord" name="selectedRecord">
<c:forEach var="item" items=${storylist.bt} >
<option>${item.tarr}</option>
</c:forEach>
</select>
<input type="submit" value="Submit">
</form>
</body>
</html>
但是，当我启动服务器上TitlePopulatorServlet这是行不通的。
我在哪里在迭代脚麻/ EL？
But when I launch the TitlePopulatorServlet on the server it doesn't work. Where am I going wrong in the iteration/EL?
推荐答案
该servlet存储列表中的要求，命名为BT的属性下。因此，它已经存在，在请求中。没有必要做
The servlet store the list in the request, under the attribute named "bt". So it's already there, in the request. There is no need to do
<jsp:useBean id="storylist" class="serv.TitlePopulatorServlet" scope="request" />
这只会造成你的servlet，它没有任何意义的新实例。和BT是一个请求属性。这不是在servlet的属性。因此，使用 $ {storylist.bt} 没有任何意义无论是。
That will only create a new instance of your servlet, which doesn't make any sense. and bt is a request attribute. It's not a property of the servlet. So using ${storylist.bt} doesn't make any sense either.
您想遍历的BT 的元素，因此，所有你需要的是
You want to iterate over the elements of bt, so all you need is
<c:forEach var="item" items="${bt}">
最后，BT 的每一个项目的类型为 BeanTitle 。而你正在做
${item.tarr}
这是等同于调用
beanTitle.getTarr()
和没有在BeanTitle没有塔尔财产。唯一的属性是 BTITLE （因为类的唯一吸气剂被命名为 getBTitle（））。
And there is no tarr property in BeanTitle. The only property is btitle (since the only getter of the class is named getBTitle()).
所以，你必须使用的是
${item.btitle}
您的命名是可怕的，那只有让你更糊涂了。你为什么不使用真正的单词来命名你的类和属性？例如像
Your naming is awful, and that only makes you more confused. Why don't you use real words to name your classes and properties? Like for example
public class Book {
private String title;
public String getTitle()
...
}
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