我在从 .jsp 文件中的组合框获取值到 servlet 时遇到问题。 我在其他 servlet 中使用方法 request.getParameter 并且它有效。在这个类中它没有。 我也试图从文本字段获取值到这个 servlet，但也不起作用。我不知道如何解决这个问题。
我有这样的组合框:
<form action="upload" method="POST" enctype="multipart/form-data">
<p class="folders_save">Folder:
<select name="folders1" id="user">
<%
user = (User)session.getAttribute("user");
listOfFolders = user.listOfFolders();
if(listOfFolders != null){
for(File file : listOfFolders){
out.print("<option value="+file.getName()+">"+file.getName()+"</option>");
}
}
%>
</select>
</p>
<input class="pole" type="file" name="file" />
<input class="wrzuc" type="submit" value="Wrzuc!">
</form>
我想获得值(value):
String folder = request.getParameter("folders1");
我的jsp文件
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org /TR/html4/loose.dtd">
<html>
<head>
<%@ page import="tools.User" %>
<%@ page import="java.io.File" %>
<%@ page import="java.text.DecimalFormat" %>
<%@page language="Java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<link rel="stylesheet" type="text/css" href="style.css" />
<title>Serwer dysku sieciowego </title>
</head>
<body>
<div class="container">
<div class="ramka_zaproszenie">
<%
File[] listOfFolders;
User user;
String username;
String status = null;
if(session.getAttribute("user")!=null){
user = (User)session.getAttribute("user");
username = user.getLogin();
status = user.getType().toString();
} else {
username = "unknown";
}
%>
<p class="loguj">Witaj, <%= username %>!</p><br>
<% if(session.getAttribute("user")!=null){ %>
<p class="tekst">Wrzuc plik na serwer:</p>
<form action="upload" method="POST" enctype="multipart/form-data">
<p class="folders_save">Folder:
<select name="folders1" id="user">
<%
user = (User)session.getAttribute("user");
listOfFolders = user.listOfFolders();
if(listOfFolders != null){
for(File file : listOfFolders){
out.print("<option value="+file.getName()+">"+file.getName()+"</option>");
}
}
%>
</select>
</p>
<input class="pole" type="file" name="file" />
<input class="wrzuc" type="submit" value="Wrzuc!">
</form>
<form action="folder" method="get">
<p class="tekst"> Folder: <br><input class="pole" id="Folder" type="text" name="folderName" />
<br /></p>
<input class="zatwierdz" type="submit" id="submit" value="Utwórz" /><br>
</form>
<br />
<% if(status.equalsIgnoreCase("ADMIN")){ %>
<a class="wroc" href="zmiana_rozmiaru.jsp">Zmiana Pojemnosci</a>
<%}%>
<br />
<br />
<p class="tekst">Posiadane pliki na serwerze:</p>
<form method="post">
Folder:
<select name="folders">
<option value=0 selected="selected" >Wybierz folder</option>
<%
user = (User)session.getAttribute("user");
listOfFolders = user.listOfFolders();
if(listOfFolders != null){
for(File file : listOfFolders){
out.print("<option value="+file.getName()+">"+file.getName()+"</option>");
}
}
%>
</select>
<input type="submit" value="Wybierz"><br>
</form>
<br />
Pliki z folderu: <%=request.getParameter("folders")%>
<center><table id="tabela">
<tr class="alt">
<th>Nazwa</th>
<th>Rozmiar</th>
<th>Pobierz</th>
<th>Usun</th>
</tr>
<%
System.out.println(request.getParameter("folders"));
user = (User)session.getAttribute("user");
File[] listOfFiles = user.listOfFiles(request.getParameter("folders"));
if(listOfFiles != null){
for(File file : listOfFiles){
DecimalFormat twoDForm = new DecimalFormat("#.##");
out.print("<tr class=\"alt\"><td>" + file.getName()+"</td><td>" +twoDForm.format((double)file.length()/1024.0)+" KB</td><td align=center> <a href=\"download?filePath="+file.getAbsolutePath()+"\"><img border=\"0\" src=\"downloadsmall.png\"></a></td><td align=center><a src=\"deletesmall.png\" href=\"delete?filePath="+file.getAbsolutePath()+"\" ><img border=\"0\" src=\"deletesmall.png\"></a></td></tr>");
}
}
%>
</table>
</center><br>
<form action="logout" method="post">
<input type="image" src="wylacznik.png" id="submit">
</form>
<br><br>
<%
if (session.getAttribute("warning") != null) {
%>
<span><%= session.getAttribute("warning") %></span>
<%
session.removeAttribute("warning");
}
%>
<% } %>
<div class="footer">Copyright 2013 by JavaProjectTeam.</div>
</div>
</div>
</body>
</html>
还有我的servlet文件
<pre>package servlets;
import java.io.*;
import java.sql.SQLException;
import java.util.*;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.servlet.annotation.WebServlet;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
import java.sql.Connection;
import java.text.DecimalFormat;
import java.text.DecimalFormatSymbols;
import tools.Connector;
import tools.User;
@WebServlet("/upload")
public class UploadServlet extends HttpServlet {
private boolean isMultipart;
private String filePath;
private File file ;
public void init(){
// Get the file location where it would be stored.
filePath = getServletContext().getInitParameter("file-upload");
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, java.io.IOException {
// Check that we have a file upload request
request.setCharacterEncoding("UTF-8");
String folder = request.getParameter("folders1");
HttpSession session = request.getSession(true);
User user = (User)session.getAttribute("user");
isMultipart = ServletFileUpload.isMultipartContent(request);
response.setContentType("text/html");
java.io.PrintWriter out = response.getWriter( );
if( !isMultipart ){
session.setAttribute("warning", "Nie masz zadnych plikow");
response.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
response.setHeader("Location", "hello.jsp");
return;
}
DiskFileItemFactory factory = new DiskFileItemFactory();
// Create a new file upload handler
ServletFileUpload upload = new ServletFileUpload(factory);
// maximum file size to be uploaded.
upload.setSizeMax(user.getSpace() * 1024);
try{
// Parse the request to get file items.
List fileItems = upload.parseRequest(request);
// Process the uploaded file items
Iterator i = fileItems.iterator();
while ( i.hasNext () )
{
FileItem fi = (FileItem)i.next();
if ( !fi.isFormField () )
{
// Get the uploaded file parameters
String fileName = fi.getName();
// Write the file
if( fileName.lastIndexOf("\\") >= 0 ){
file = new File( filePath+"\\"+user.getId()+"\\"+folder+"\\"+
fileName.substring( fileName.lastIndexOf("\\"))) ;
}else{
file = new File( filePath+"\\"+user.getId()+"\\"+folder+"\\"+
fileName.substring(fileName.lastIndexOf("\\")+1)) ;
}
fi.write(file);
System.out.println(file.getName());
try{
Connection connection = new Connector().getConnection();
DecimalFormatSymbols otherSymbols = new DecimalFormatSymbols(Locale.GERMAN);
otherSymbols.setDecimalSeparator('.');
otherSymbols.setGroupingSeparator('.');
DecimalFormat twoDForm = new DecimalFormat("#.##", otherSymbols);
System.out.println(twoDForm.format((double)file.length()/1024.0));
connection.createStatement().executeUpdate("UPDATE `users` SET `space` = `space`-"+twoDForm.format((double)file.length()/1024.0)+" where id="+user.getId());
} catch(SQLException e){
e.printStackTrace();
}
session.setAttribute("warning", "Plik został dodany do wirtualnego dysku.");
response.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
response.setHeader("Location", "hello.jsp");
}
}
out.println("</body>");
out.println("</html>");
}catch(Exception ex) {
System.out.println(ex);
session.setAttribute("warning", "File is too big! Only "+user.getSpace()+"KB left.");
response.setStatus(HttpServletResponse.SC_MOVED_TEMPORARILY);
response.setHeader("Location", "hello.jsp");
}
}
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, java.io.IOException {
throw new ServletException("GET method used with " +
getClass( ).getName( )+": POST method required.");
}
}<code>
最佳答案
这是因为您要发送 multipart/form-data 默认情况下 servlet 不支持请求。但是，我注意到您仍在使用“旧版”Apache Commons FileUpload 来获取上传的文件，而不是使用新的 Servlet 3.0 提供 HttpServletRequest#getPart() .在这种情况下，您基本上有 2 个选择:
坚持使用 Commons FileUpload。您应该在
else中收集常规表单字段你的 blockif (!fi.isFormField())您目前完全忽略了这一点。if (!fi.isFormField()) { // Collect uploaded file from fi. } else { // Collect normal form field from fi. }摆脱 Commons FileUpload 并使用
@MultipartConfig注释。@WebServlet("/upload") @MultipartConfig public class UploadServlet extends HttpServlet {这样你可以通过
request.getPart()获取文件并继续使用request.getParameter()常规表单字段的常用方法。
另见:
与具体问题无关，那不是组合框，而是下拉列表。组合框是一个可编辑的下拉列表。此外，在 JSP 中编写 Java 代码是一种不好的做法。 Java 代码像 servlet 一样属于 Java 类。要循环选项，请使用 JSTL <c:forEach> .而且，在像 servlet 这样的 Java 类中编写 HTML 代码是一种不好的做法。 HTML 代码属于 JSP 文件。使用 RequestDispatcher#forward()在 JSP 中显示结果。另见 our servlets wiki page .
哦，您的 servlet 中存在一个主要的线程安全问题。在所有 HTTP 请求之间共享的应用程序生命周期中只有一个 servlet 实例。那些领域
private boolean isMultipart;
private String filePath;
private File file ;
将在所有 HTTP 请求之间共享，从而在多个用户同时使用同一个 servlet 时导致潜在的重大问题。摆脱它们并将它们移动到 doXxx() 内部方法 block 。
关于java - 从组合框获取值(value)到jsp中的servlet，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/14872834/