Java中Jsp和Servlet上传和下载文件

旧城等待， 2023-05-31 10:09 7阅读 0赞

## 上传： ##

**前端页面：**

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>file_up_test</title>
        <style type="text/css">
            #main {
                margin: 200px auto auto 200px;
            }
        </style>
    </head>
    <body>
    <%--enctype:--%>
    <%--1.application/x-www-form-urlencoded（默认）--%>
    <%--2.multipart/form-data（二进制编码）--%>
    <%--注意：使用二进制编码后Servlet无法使用req.getParam来获取参数--%>
    <form action="${pageContext.request.contextPath}/FileUpTest" method="post" enctype="multipart/form-data">
        <div id="main">
            <div>
                选择用户名:
                <select id="selUser" name="userName" style="width: 120px; height: 30px">
                    <option value="1">kobe</option>
                    <option value="2">james</option>
                </select>
            </div>
            <br/>
            <div>
                选择文件：
                <%--这个约束没什么用--%>
                <input type="file" id="fileUp" name="fileUp" multiple="multiple" accept="image/*"
                       style="width: 300px; height: 30px"/>
            </div>
            <br/>
            <div>
                <input type="submit" value="提交" style="width: 120px; height: 30px"/>
            </div>
        </div>
    
    </form>
    </body>
    </html>

**后台代码：**

package com.study.jsp.test;
    
    import com.jdbc.library.common.FileUpUtil;
    import org.apache.commons.fileupload.disk.DiskFileItemFactory;
    import org.apache.commons.fileupload.servlet.ServletFileUpload;
    import org.apache.commons.io.*;
    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 java.io.*;
    import java.text.SimpleDateFormat;
    import java.util.Date;
    import java.util.Map;
    
    
    @WebServlet("/FileUpTest")
    public class FileUpTestServlet extends HttpServlet {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            req.setCharacterEncoding("UTF-8");
            resp.setContentType("text/html;charset=UTF-8");
            boolean isFileForm = ServletFileUpload.isMultipartContent(req);
            if (!isFileForm) {
                return;
            }
            FileUpUtil fileUpUtil = new FileUpUtil(req);
            //保存文件
            saveFile(req, fileUpUtil);
            //获取参数
            Map<String, String> paraMap = fileUpUtil.getFormPara();
            String userName = paraMap.get("userName");
            resp.getWriter().write(userName);
        }
    
        /**
         * 关于上传文件
         */
        private void aboutFile(HttpServletRequest req) {
            try {
                /*********************一.唯一标识**************************/
                //1.唯一标识1
                String dateStr = new SimpleDateFormat("yyyyMMddHHmmsssss").format(new Date());
                //2.唯一标识2
                //String uuId = UUID.randomUUID().toString();
                // (例如：美女.jsp)
                //3.唯一标识3
                //long milSeconds = new Date().getTime();
                /*********************二.文件扩展名**************************/
                //1.获取文件扩展名
                String fileName = "美女.jpg";
                //美女.jpg
                String name = FilenameUtils.getName(fileName);
                //美女
                String baseName = FilenameUtils.getBaseName(fileName);
                //jpg
                String extenName = FilenameUtils.getExtension(fileName);
                //美女.jpg
                String fullName = FilenameUtils.getFullPath(fileName);
                /*******************三.缓存大小和临时目录**************************/
                DiskFileItemFactory factory = new DiskFileItemFactory();
                //1.设置缓存大小(单位：字节 默认大小：10240字节=10kb)
                factory.setSizeThreshold(1024 * 1024 * 10);//10兆
                //2.设置临时目录(不建议更改)
                factory.setRepository(new File(""));
                /*******************四.文件大小限制**************************/
                ServletFileUpload fileUpload = new ServletFileUpload(factory);
                //1.单个上传文件大小(单位：字节 默认大小：2097152字节=2兆)
                fileUpload.setFileSizeMax(1024 * 1024 * 10);//10兆
                //2.一次完整请求的所有上传数据+文件大小
                fileUpload.setSizeMax(1024 * 1024 * 20);//20兆
    
            } catch (Exception ex) {
            }
        }
    
        /**
         * 保存文件
         *
         * @param req
         */
        private void saveFile(HttpServletRequest req, FileUpUtil fileUpUtil) {
            //1.唯一标识1
            String dateStr = new SimpleDateFormat("yyyyMMddHHmmsssss").format(new Date());
            String dirStr = "/upload/" + dateStr + "";
            // (不可用)获取的是磁盘根目录的绝对路径（D:/img/1234565555）
            // String xDirPath = dir.getAbsolutePath();
            // (可用)获取的是web文件夹下面的绝对路径（D:/img/1234565555）
            String xDirPath = req.getServletContext().getRealPath(dirStr);
            File dir = new File(xDirPath);
            if (!dir.exists()) {
                dir.mkdirs();
            }
            fileUpUtil.saveFormFile(xDirPath, "");
        }
    }

package com.jdbc.library.common;
    
    import org.apache.commons.fileupload.FileItem;
    import org.apache.commons.fileupload.FileUploadException;
    import org.apache.commons.fileupload.disk.DiskFileItemFactory;
    import org.apache.commons.fileupload.servlet.ServletFileUpload;
    
    import javax.servlet.http.HttpServletRequest;
    import java.io.File;
    import java.util.HashMap;
    import java.util.List;
    import java.util.Map;
    
    public class FileUpUtil {
    
        private HttpServletRequest _res;
        private DiskFileItemFactory _factory;
        private ServletFileUpload _fileUpload;
        private Map<String, String> _paraMap = new HashMap<String, String>();
    
        public FileUpUtil(HttpServletRequest res) {
            _res = res;
            _factory = new DiskFileItemFactory();
            _fileUpload = new ServletFileUpload(_factory);
        }
    
        /**
         * 保存上传文件到本地
         *
         * @param xDirPath  文件绝对路径（不包含文件名）
         * @param xFileName 文件名（图片.JPG）
         */
        public void saveFormFile(String xDirPath, String xFileName) {
            try {
                List<FileItem> fileItemList = _fileUpload.parseRequest(_res);
                for (FileItem fileItem : fileItemList) {
                    //是否存储在内存中
                    fileItem.isInMemory();
                    //找到文件类型参数
                    if (!fileItem.isFormField()) {
                        String fileName = xFileName.length() > 0 ? xFileName : fileItem.getName();
                        String absoluRootPath = xDirPath.length() > 0 ? xDirPath : _res.getServletContext().getRealPath(_res.getServletContext().getInitParameter("FileUpPath"));
                        String path = absoluRootPath + "/" + fileName;
                        fileItem.write(new File(path));
                    } else {
                        String paraName = fileItem.getFieldName();
                        String paraVal = fileItem.getString();
                        _paraMap.put(paraName, paraVal);
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        /**
         * 获取所有参数名和参数值(除去file类型参数)
         *
         * @return
         */
        public Map<String, String> getFormPara() {
            return _paraMap;
        }
    
    
    }

## 下载： ##

**前端页面：**

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
    <html>
    <head>
        <title>file_download</title>
    </head>
    <body>
    
    <%--GET请求:后台验证--%>
    <%--<a href="${pageContext.request.contextPath}/FileDownTest?fileName=测试.jpg">点击下载</a>--%>
    
    <%--POST请求:后台验证--%>
    <form action="${pageContext.request.contextPath}/FileDownTest">
        <img src="${pageContext.request.contextPath}/upload/测试.jpg" width="200"
             height="200"/>
        <%--无法保证下载安全--%>
        <%--<a href="${pageContext.request.contextPath}/img/测试.jpg">点击下载</a>--%>
        <input type="hidden" name="fileName" value="测试.jpg"/>
        <input type="submit" value="点击下载" style="width:120px; height: 30px"/>
    </form>
    </body>
    </html>

**后台代码：**

package com.study.jsp.test;
    
    import javax.servlet.ServletException;
    import javax.servlet.ServletOutputStream;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.IOException;
    import java.net.URLEncoder;
    import java.nio.file.Files;
    import java.nio.file.Paths;
    
    @WebServlet("/FileDownTest")
    public class FileDownTestServlet extends HttpServlet {
        @Override
        protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            //GET请求设置Server.xml的Connector
            //POST请求设置
            req.setCharacterEncoding("UTF-8");
            String fileName = req.getParameter("fileName");
            if(fileName==null||"".equals(fileName))
            {
                return;
            }
            //GET请求不需要二次编码，POST请求需要二次编码
            fileName = req.getMethod().toLowerCase().equals("get") ? fileName : new String(fileName.getBytes("ISO-8859-1"), "utf-8");
            //找到资源的位置，读取到内存，响应给浏览器：
            String realPath = super.getServletContext().getRealPath(super.getServletContext().getInitParameter("FileDownPath"));
            String filePath = realPath + "\\" + fileName;
            ServletOutputStream out = resp.getOutputStream();
            //设置响应头
            resp.setContentType("application/x-msdownload");
            //获取请求头信息Use-Agent
            String userAgent = req.getHeader("User-Agent");
            if (userAgent.contains("MSIE")) {
                //IE
                fileName = URLEncoder.encode(fileName, "UTF-8");
            } else {
                //非IE
                fileName = new String(fileName.getBytes("UTF-8"), "ISO-8859-1");
            }
            //设置下载的文件名称
            resp.setHeader("Content-Disposition", "attachment;fileName=" + fileName);
            //将数据响应到浏览器
            Files.copy(Paths.get(filePath), out);
        }
    }