Jsp文件上传

表单 enctype 属性应该设置为 multipart/form-data.
需要引入的 jar 文件：commons-fileupload-1.3.2、commons-io-2.5.jar。

upload.jsp : 文件上传表单

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>文件上传</title>
</head>
<body>
<form  action="UploadServlet" method="post" enctype="multipart/form-data">
   选择一个文件:
   <input type="file" name="uploadFile"/>
   <br/><br/>
   <input type="submit" value="上传"/>
</form>
</body>
</html>

message.jsp : 上传成功后跳转页面。

<%@ page language="java" contentType="text/html; charset=UTF-8"
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>文件上传结果</title>
</head>
<body>
    <center>
        <h2>${message}</h2>
    </center>
</body>
</html>

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"
    id="WebApp_ID" version="2.5">
  <servlet>
    <display-name>UploadServlet</display-name>
    <servlet-name>UploadServlet</servlet-name>
    <servlet-class>com.tanlei.test.UploadServlet</servlet-class>
  </servlet>
   
  <servlet-mapping>
    <servlet-name>UploadServlet</servlet-name>
    <url-pattern>/UploadServlet</url-pattern>
  </servlet-mapping>
</web-app>

UploadServlet.java : 上传处理 Servlet。

package com.tanlei.test;

import java.io.File;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.List;

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 UploadServlet extends HttpServlet {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    
    //上传文件存储目录
    private static  final String UPLOAD_DIRECTORY="upload";
    
    //上传配置
    private static final int MEMORY_THRESHOLD=1024*1024*3;//3MB
    private static final int MAX_FILE_SIZE= 1024 * 1024 * 40; // 40MB
    private static final int MAX_REQUEST_SIZE= 1024 * 1024 * 50; // 50MB

    
    /**
     * 上传数据及保存文件
     */
    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
            throws ServletException, IOException {
    //检测是否为多媒体上传
        if(!ServletFileUpload.isMultipartContent(req)) {
            //如果不是则停止
            PrintWriter writer=resp.getWriter();
            writer.println("Error: 表单必须包含 enctype=multipart/form-data");
            writer.flush();
            return;
        }
        
        //配置上传参数
        DiskFileItemFactory factory=new DiskFileItemFactory();
        //设置内存临界值-超过后将产生临时文件并存储于临时目录中
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        //设置临时存储目录
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));
        
        ServletFileUpload upload=new ServletFileUpload(factory);
        
        //设置最大文件上传值
        upload.setFileSizeMax(MAX_FILE_SIZE);
        
        //设置最大请求值(包含文件和表单数据)
        upload.setFileSizeMax(MAX_REQUEST_SIZE);
        
        //中文处理
        upload.setHeaderEncoding("UTF-8");
        
        //构造临时路径来存储上传的文件
        //这个路径相对当前应用的目录
        String uploadPath=getServletContext().getRealPath("/")+ File.separator + UPLOAD_DIRECTORY;

        //如果目录不存在则创建
        File uploadDir=new File(uploadPath);
        if(uploadDir.exists()) {
            uploadDir.mkdir();
        }
        try {
            // 解析请求的内容提取文件数据
            @SuppressWarnings("unchecked")
            List<FileItem> formItems = upload.parseRequest(req);
 
            if (formItems != null && formItems.size() > 0) {
                // 迭代表单数据
                for (FileItem item : formItems) {
                    // 处理不在表单中的字段
                    if (!item.isFormField()) {
                        String fileName = new File(item.getName()).getName();
                        String filePath = uploadPath + File.separator + fileName;
                        File storeFile = new File(filePath);
                        // 在控制台输出文件的上传路径
                        System.out.println(filePath);
                        // 保存文件到硬盘
                        item.write(storeFile);
                        req.setAttribute("message",
                            "文件上传成功!");
                    }
                }
            }
        } catch (Exception ex) {
            req.setAttribute("message",
                    "错误信息: " + ex.getMessage());
        }
        // 跳转到 message.jsp
        getServletContext().getRequestDispatcher("/message.jsp").forward(
                req, resp);
    
    }
    
    
}