request doesn't contain a multipart/form-data or multipart/mixed stream
form的enctype属性为编码方式，常用有两种：application/x-www-form-urlencoded和multipart/form-data，默认为application/x-www-form-urlencoded。?
当action为get时候，浏览器用x-www-form-urlencoded的编码方式把form数据转换成一个字串（name1=value1&name2=value2...），然后把这个字串append到url后面，用?分割，加载这个新的url。?
当action为post时候，浏览器把form数据封装到http body中，然后发送到server。?
如果没有type=file的控件，用默认的application/x-www-form-urlencoded就可以了。?
但是如果有type=file的话，就要用到multipart/form-data了。浏览器会把整个表单以控件为单位分割，并为每个部分加上Content-Disposition(form-data或者file),Content-Type(默认为text/plain),name(控件name)等信息，并加上分割符(boundary)。?
如果有以下form，并选择了file1.txt上传?
<form action="http://server.com/cgi/handle"?
?????? enctype="multipart/form-data"?
?????? method="post">?
?? <input type="text" name="submit-name" value="chmod777"><br />?
?? What files are you sending? <input type="file" name="files"><br />?
</form>?
则有如下body:?
Content-Type: multipart/form-data; boundary=AaB03x?
?? --AaB03x?
?? Content-Disposition: form-data; name="submit-name"?
?? chmod777?
?? --AaB03x?
?? Content-Disposition: form-data; name="files"; filename="file1.txt"?
?? Content-Type: text/plain?
?? ... contents of file1.txt ...?
?? --AaB03x--
?
1.上传组件
①Apache的Commons FileUpload
②JavaZoom的UploadBean
③JspSmartUpload
2.下载Commons的FileUpload组件
地址:http://commons.apache.org/fileupload/
同时还要下载Commons的IO组件
地址:http://commons.apache.org/io/
3.使用实例
步骤一：创建文件上传的页面：fileUpload.jsp
注意表单的 enctype 属性，这个设置很重要，详情请见：http://www.cnblogs.com/yinger/archive/2011/09/11/2173689.html
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
? <head>
??? <title>文件上传</title>
? </head>
? <body>
????? <form action="<%=request.getContextPath() %>/servlet/FileUploadServlet" method="post" enctype="multipart/form-data" >
??????? 上传人名:<input type="text" name="name" /><br/>?????
????????? 上传文件:<input type="file" name="file" /><br/>
????????? <input type="submit" name="submit" value="提交" />
????? </form>
? </body>
</html>
步骤二：创建处理文件上传的servlet：fileUploadServlet
package com.yinger.servlet;
import java.io.File;
import java.io.IOException;
import java.util.Iterator;
import java.util.List;
import javax.servlet.ServletConfig;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.apache.commons.fileupload.FileItem;
import org.apache.commons.fileupload.disk.DiskFileItemFactory;
import org.apache.commons.fileupload.servlet.ServletFileUpload;
public class FileUploadServlet extends HttpServlet {
???
??? private ServletContext sc;
??? private String savePath;
??? private static final long serialVersionUID = 151650843430214502L;
??? public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
??????? doPost(request, response);
??? }
??? public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
???????
??????? request.setCharacterEncoding("UTF-8");
???
??????? DiskFileItemFactory factory = new DiskFileItemFactory();
??????? ServletFileUpload servletFileUpload = new ServletFileUpload(factory);//通过工厂生成一个处理文件上传的servlet对象
???????
??????? try {
??????????? List items = servletFileUpload.parseRequest(request);//解析request
??????????? Iterator iterator = items.iterator();
??????????? while (iterator.hasNext()) {
??????????????? FileItem item = (FileItem) iterator.next();
??????????????? if(item.isFormField()){//表单的参数字段
??????????????????? System.out.println("表单的参数名称："+item.getFieldName()+",表单的参数值："+item.getString("UTF-8"));
??????????????? }else {
??????????????????? if(item.getName()!=null && !item.getName().equals("")){//一个上传的文件
??????????????????????? System.out.println("文件的名称："+item.getName());
??????????????????????? System.out.println("文件的大小："+item.getSize());
??????????????????????? System.out.println("文件的类型："+item.getContentType());
???????????????????????
??????????????????????? File tempFile = new File(item.getName());//getName得到的文件名称包含了它在客户端的路径
??????????????????????? File file = new File(sc.getRealPath("/")+savePath,tempFile.getName());
??????????????????????? item.write(file);//将上传的文件写入到file中
???????????????????????
??????????????????????? request.setAttribute("message", "上传文件成功！");
??????????????????? }else{
??????????????????????? request.setAttribute("message", "没有选择上传文件！");
??????????????????? }
??????????????? }
??????????? }
??????? } catch (Exception e) {
??????????? e.printStackTrace();
??????????? request.setAttribute("message", "上传文件失败！");
??????? }
???????
??????? request.getRequestDispatcher("/fileUploadResult.jsp").forward(request, response);//转向，输出结果
??? }
??? @Override
??? public void init(ServletConfig config) throws ServletException {
??????? savePath = config.getInitParameter("savePath");
??????? sc = config.getServletContext();???????
??? }
???
}
步骤三：修改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_2_5.xsd" version="2.5">
? <display-name></display-name>
? <servlet>
??? <description>This is the description of my J2EE component</description>
??? <display-name>This is the display name of my J2EE component</display-name>
??? <servlet-name>FileUploadServlet</servlet-name>
??? <servlet-class>com.yinger.servlet.FileUploadServlet</servlet-class>
??? <init-param> <!-- Servlet的初始化参数，配置上传文件的保存路径，这里是当前应用的uplods目录下 -->
??? <param-name>savePath</param-name>
??? <param-value>uploads</param-value>
??? </init-param>
? </servlet>
? <servlet-mapping>
??? <servlet-name>FileUploadServlet</servlet-name>
??? <url-pattern>/servlet/FileUploadServlet</url-pattern>
? </servlet-mapping>
? <welcome-file-list>
??? <welcome-file>index.jsp</welcome-file>
? </welcome-file-list>
</web-app>
同时在项目的根目录下创建文件夹 uploads （可以就在WebRoot中创建）
步骤四：创建显示上传结果的页面：fileUploadResult.jsp
<%@ page language="java" pageEncoding="UTF-8"%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
? <head>
??? <title>文件上传</title>
? </head>
? <body>
? <p>
????? ${requestScope['message'] }<br/>
? </p>
? </body>
</html>
效果展示
?