Java Web Servlet 上传和下载文件

水深无声 2023-09-30 09:20 16阅读 0赞

在本文中，我将讨论**如何在 servlet 中上传和下载文件到服务器。**在本文的最后，您将了解如何在基于 Servlet 的 Java Web 应用程序中设置文件上传和文件下载功能。作为本示例的一部分，我们创建了以下文件：

1.  **fileupload.jsp**
2.  **allfiles.jsp**
3.  **fileuploadResponse.jsp**
4.  **UploadDetail.java**
5.  **FileUploadServlet.java**
6.  **UploadedFileServlet.java**
7.  **FileDownloadServlet.java**
8.  **web.xml**
9.  **main.css**

**UploadDetail.java**是一个 POJO 类，用于存储上传的文件状态，即文件名、文件状态和文件上传状态。**FileUploadServlet.java**是一个用于上传文件的控制器类。servlet 使用带有文件大小阈值、最大文件大小和最大请求大小的 @Multipartconfig 注释进行注释。**UploadedFileServlet.java**是一个控制器类，用于显示已经上传到服务器的文件。**FileDownloadServlet.java**用于从服务器下载文件。

**fileupload.jsp**页面包含上传单个文件或多个文件的上传表单。**FileUploadResponse.jsp**页面用于显示上传文件的结果。在这个JSP中，我们遍历uploadDetail对象列表，打印上传文件信息的表格数据。此外，在此页面上，我们创建了最后一列作为上传文件的下载链接。**allfiles.jsp**页面用于显示驻留在服务器上的文件总数的结果。**web.xml**是一个部署描述符，包含有关 servlet 的信息。**main.css**是用于描述文档外观和格式的样式表。

**fileupload.jsp**

<%@ page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
            <title>Servlet File Upload/Download</title>
            <link rel="stylesheet" href="resource/css/main.css" />
        </head>
        <body>
            <div class="panel">
                <h1>File Upload</h1>
                <h3>Press 'CTRL' Key+Click On File To Select Multiple Files in Open Dialog</h3>
                <form id="fileUploadForm" method="post" action="fileUploadServlet" enctype="multipart/form-data">
                    <div class="form_group">
                        <label>Upload File</label><span id="colon">: </span><input id="fileAttachment" type="file" name="fileUpload" multiple="multiple" />
                        <span id="fileUploadErr">Please Upload A File!</span>
                    </div>
                    <button id="uploadBtn" type="submit" class="btn btn_primary">Upload</button>
                </form>
            </div>
    
            
            <div class="panel">
                <a id="allFiles" class="hyperLink" href="<%=request.getContextPath()%>/uploadedFilesServlet">List all uploaded files</a>
            </div>
        </body>
    </html>

**allfiles.jsp**

<%@page import="java.util.List"%>
    <%@page import="com.jcg.servlet.UploadDetail"%>
    <%@page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
            <title>Servlet File Upload/Download</title>
    
            <link rel="stylesheet" href="resource/css/main.css" />
        </head>
        <body>
            <div class="panel">
                <h1>Uploaded Files</h1>
                <table class="bordered_table">
                    <thead>
                        <tr align="center"><th>File Name</th><th>File Size</th><th>Action</th></tr>
                    </thead>
                    <tbody>
                        <% List<UploadDetail> uploadDetails = (List<UploadDetail>) request.getAttribute("uploadedFiles");
                            if (uploadDetails != null && uploadDetails.size() > 0) {
                                for (int i = 0; i < uploadDetails.size(); i++) {
                        %>
                        <tr>
                            <td align="center"><span id="fileName"><%=uploadDetails.get(i).getFileName()%></span></td>
                            <td align="center"><span id="fileSize"><%=uploadDetails.get(i).getFileSize()%> KB</span></td>
                            <td align="center"><span id="fileDownload"><a id="downloadLink" class="hyperLink" href="<%=request.getContextPath()%>/downloadServlet?fileName=<%=uploadDetails.get(i).getFileName()%>">Download</a></span></td>
                        </tr>
                        <% }
                      } else { %>
                        <tr>
                            <td colspan="3" align="center"><span id="noFiles">No Files Uploaded.....!</span></td>
                        </tr>
                        <% }%>
                    </tbody>
                </table>
                <div class="margin_top_15px">
                    <a id="fileUpload" class="hyperLink" href="<%=request.getContextPath()%>/fileupload.jsp">Back</a>
                </div>
            </div>
        </body>
    </html>

**fileuploadResponse.jsp**

<%@page import="java.util.List"%>
    <%@page import="com.servlet.UploadDetail"%>
    <%@page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>
    <!DOCTYPE html>
    <html>
        <head>
            <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
            <title>Servlet File Upload/Download</title>
    
            <link rel="stylesheet" href="resource/css/main.css" />
        </head>
        <body>
            <div class="panel">
                <h1>File Upload Status</h1>
                <table class="bordered_table">
                    <thead>
                        <tr align="center"><th>File Name</th><th>File Size</th><th>Upload Status</th><th>Action</th></tr>
                    </thead>
                    <tbody>
                        <% List<UploadDetail> uploadDetails = (List<UploadDetail>) request.getAttribute("uploadedFiles");
                            for (int i = 0; i < uploadDetails.size(); i++) {
                        %>
                        <tr>
                            <td align="center"><span id="fileName"><%=uploadDetails.get(i).getFileName()%></span></td>
                            <td align="center"><span id="fileSize"><%=uploadDetails.get(i).getFileSize()%> KB</span></td>
                            <td align="center"><span id="fileuploadStatus"><%=uploadDetails.get(i).getUploadStatus()%></span></td>
                            <td align="center"><span id="fileDownload"><a id="downloadLink" class="hyperLink" href="<%=request.getContextPath()%>/downloadServlet?fileName=<%=uploadDetails.get(i).getFileName()%>">Download</a></span></td>
                        </tr>
                        <% }%>
                    </tbody>
                </table>
                <div class="margin_top_15px">
                    <a id="fileUpload" class="hyperLink" href="<%=request.getContextPath()%>/fileupload.jsp">Back</a>
                </div>
            </div>
        </body>
    </html>

**UploadDetail.java**

package com.servlet;
    
    
    import java.io.Serializable;
    
    public class UploadDetail implements Serializable {
    
        private long fileSize;
        private String fileName, uploadStatus;
    
        private static final long serialVersionUID = 1L;
    
        public long getFileSize() {
            return fileSize;
        }
    
        public void setFileSize(long fileSize) {
            this.fileSize = fileSize;
        }
    
        public String getFileName() {
            return fileName;
        }
    
        public void setFileName(String fileName) {
            this.fileName = fileName;
        }
    
        public String getUploadStatus() {
            return uploadStatus;
        }
    
        public void setUploadStatus(String uploadStatus) {
            this.uploadStatus = uploadStatus;
        }
    }

**FileUploadServlet.java**

package com.servlet;
    
    
    import java.io.File;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.List;
    import javax.servlet.RequestDispatcher;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.MultipartConfig;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import javax.servlet.http.Part;
    
    @WebServlet(description = "Upload File To The Server", urlPatterns = {"/fileUploadServlet"})
    @MultipartConfig(fileSizeThreshold = 1024 * 1024 * 10, maxFileSize = 1024 * 1024 * 30, maxRequestSize = 1024 * 1024 * 50)
    public class FileUploadServlet extends HttpServlet {
    
        private static final long serialVersionUID = 1L;
        public static final String UPLOAD_DIR = "uploadedFiles";
    
        /**
         * *** This Method Is Called By The Servlet Container To Process A 'POST'
         * Request ****
         */
        public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            handleRequest(request, response);
        }
    
        public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
            /**
             * *** Get The Absolute Path Of The Web Application ****
             */
            String applicationPath = getServletContext().getRealPath(""),
                    uploadPath = applicationPath + File.separator + UPLOAD_DIR;
    
            File fileUploadDirectory = new File(uploadPath);
            if (!fileUploadDirectory.exists()) {
                fileUploadDirectory.mkdirs();
            }
    
            String fileName = "";
            UploadDetail details = null;
            List<UploadDetail> fileList = new ArrayList<UploadDetail>();
    
            for (Part part : request.getParts()) {
                fileName = extractFileName(part);
                details = new UploadDetail();
                details.setFileName(fileName);
                details.setFileSize(part.getSize() / 1024);
                try {
                    part.write(uploadPath + File.separator + fileName);
                    details.setUploadStatus("Success");
                } catch (IOException ioObj) {
                    details.setUploadStatus("Failure : " + ioObj.getMessage());
                }
                fileList.add(details);
            }
    
            request.setAttribute("uploadedFiles", fileList);
            RequestDispatcher dispatcher = request.getRequestDispatcher("/fileuploadResponse.jsp");
            dispatcher.forward(request, response);
        }
    
        /**
         * *** Helper Method #1 - This Method Is Used To Read The File Names ****
         */
        private String extractFileName(Part part) {
            String fileName = "",
                    contentDisposition = part.getHeader("content-disposition");
            String[] items = contentDisposition.split(";");
            for (String item : items) {
                if (item.trim().startsWith("filename")) {
                    fileName = item.substring(item.indexOf("=") + 2, item.length() - 1);
                }
            }
            return fileName;
    
        }
    }

**UploadedFilesServlet.java**

package com.servlet;
    
    
    import com.servlet.UploadDetail;
    import java.io.File;
    import java.io.IOException;
    import java.util.ArrayList;
    import java.util.List;
    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;
    
    @WebServlet(description = "List The Already Uploaded Files", urlPatterns = {"/uploadedFilesServlet"})
    public class UploadedFilesServlet extends HttpServlet {
    
        private static final long serialVersionUID = 1L;
        public static final String UPLOAD_DIR = "uploadedFiles";
    
        /**
         * *** This Method Is Called By The Servlet Container To Process A 'GET'
         * Request ****
         */
        public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            handleRequest(request, response);
        }
    
        public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
            /**
             * *** Get The Absolute Path Of The Web Application ****
             */
            String applicationPath = getServletContext().getRealPath(""),
                    uploadPath = applicationPath + File.separator + UPLOAD_DIR;
    
            File fileUploadDirectory = new File(uploadPath);
            if (!fileUploadDirectory.exists()) {
                fileUploadDirectory.mkdirs();
            }
    
            UploadDetail details = null;
            File[] allFiles = fileUploadDirectory.listFiles();
            List<UploadDetail> fileList = new ArrayList<UploadDetail>();
    
            for (File file : allFiles) {
                details = new UploadDetail();
                details.setFileName(file.getName());
                details.setFileSize(file.length() / 1024);
                fileList.add(details);
            }
    
            request.setAttribute("uploadedFiles", fileList);
            RequestDispatcher dispatcher = request.getRequestDispatcher("/allfiles.jsp");
            dispatcher.forward(request, response);
        }
    }

**FileDownloadServlet.java**

package com.servlet;
    
    
    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.io.OutputStream;
    import javax.servlet.ServletException;
    import javax.servlet.annotation.WebServlet;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    @WebServlet(description = "Download File From The Server", urlPatterns = {"/downloadServlet"})
    public class FileDownloadServlet extends HttpServlet {
    
        private static final long serialVersionUID = 1L;
    
        public static int BUFFER_SIZE = 1024 * 100;
        public static final String UPLOAD_DIR = "uploadedFiles";
    
        /**
         * *** This Method Is Called By The Servlet Container To Process A 'GET'
         * Request ****
         */
        public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
            handleRequest(request, response);
        }
    
        public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    
            /**
             * *** Get The Absolute Path Of The File To Be Downloaded ****
             */
            String fileName = request.getParameter("fileName"),
                    applicationPath = getServletContext().getRealPath(""),
                    downloadPath = applicationPath + File.separator + UPLOAD_DIR,
                    filePath = downloadPath + File.separator + fileName;
    
            File file = new File(filePath);
            OutputStream outStream = null;
            FileInputStream inputStream = null;
    
            if (file.exists()) {
    
                /**
                 * ** Setting The Content Attributes For The Response Object ***
                 */
                String mimeType = "application/octet-stream";
                response.setContentType(mimeType);
    
                /**
                 * ** Setting The Headers For The Response Object ***
                 */
                String headerKey = "Content-Disposition";
                String headerValue = String.format("attachment; filename=\"%s\"", file.getName());
                response.setHeader(headerKey, headerValue);
    
                try {
    
                    /**
                     * ** Get The Output Stream Of The Response ***
                     */
                    outStream = response.getOutputStream();
                    inputStream = new FileInputStream(file);
                    byte[] buffer = new byte[BUFFER_SIZE];
                    int bytesRead = -1;
    
                    /**
                     * ** Write Each Byte Of Data Read From The Input Stream Write
                     * Each Byte Of Data Read From The Input Stream Into The Output
                     * Stream ***
                     */
                    while ((bytesRead = inputStream.read(buffer)) != -1) {
                        outStream.write(buffer, 0, bytesRead);
                    }
                } catch (IOException ioExObj) {
                    System.out.println("Exception While Performing The I/O Operation?= " + ioExObj.getMessage());
                } finally {
                    if (inputStream != null) {
                        inputStream.close();
                    }
    
                    outStream.flush();
                    if (outStream != null) {
                        outStream.close();
                    }
                }
            } else {
    
                /**
                 * *** Set Response Content Type ****
                 */
                response.setContentType("text/html");
    
                /**
                 * *** Print The Response ****
                 */
                response.getWriter().println("<h3>File " + fileName + " Is Not Present .....!</h3>");
            }
        }
    }

**web.xml**

<?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee        http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0">
        <display-name>Servlet File Upload/Download</display-name>
        <welcome-file-list>
            <welcome-file>fileupload.jsp</welcome-file>
        </welcome-file-list>
    </web-app>

**main.css**

* {
        box-sizing: border-box;
    }
    
    .margin_top_15px {
        margin-top: 15px;
    }
    
    .panel {
        display: block;
        padding: 15px;
        border: 1px solid #c0c0c0;
        width: 849px;
        margin: 52px 0px 0px 32px;
    }
    
    label {
        display: inline-block;
        margin-bottom: 5px;
    }
    
    .form_group {
        margin: 10px;
    }
    
    .btn_primary {
        color: #fff;
        background-color: #0275d8;
        border-color: #0275d8;
    }
    
    .btn {
        display: inline-block;
        padding: 10px;
        text-align: center;
        white-space: nowrap;
        vertical-align: middle;
        cursor: pointer;
        border: 1px solid transparent;
    }
    
    .input_error {
        color: #DE3330;
        padding: 5px;
    }
    
    .bordered_table {
        border-collapse: collapse;
        width: 100%;
        table-layout: fixed;
    }
    
    .bordered_table tr,th,td {
        border: 1px solid #333;
    }
    
    .bordered_table th,td {
        padding: 5px;
    }
    
    .bordered_table td {
        word-wrap: break-word;
    }
    
    #noFiles {
        color: red;
        font-size: larger;
    }
    
    .hyperLink {
        text-decoration: none;
        cursor: pointer;
    }

**Output**

运行您的代码以获得以下输出。点击“选择文件”，选择要上传的文件，然后点击“上传”按钮。单击“列出所有上传的文件”链接以查看已上传文件的列表。

![e103d592054a639ed23eda65c517363e.png][]

单击“上传”按钮后，您将收到以下响应。按“返回”链接返回文件上传页面。

![079f17d273b64108486227fd3850f146.png][]

单击“列出所有上传的文件”链接后，您将收到以下响应。单击“下载”链接以下载特定文件。

![6ec3259eb0400aa4b72d89145f6e3c3f.png][]

下载特定文件后，您将在此 PC -> 下载选项中找到该文件。

![a033fc55dd265f62a816ea531a9be34b.png][]

在本文中，我们开发了一个在 servlet 中上传和上传文件到服务器的应用程序，希望您喜欢这篇**如何在 servlet 中上传和下载文件到服务器的**文章。

[e103d592054a639ed23eda65c517363e.png]: https://img-blog.csdnimg.cn/img_convert/e103d592054a639ed23eda65c517363e.png
[079f17d273b64108486227fd3850f146.png]: https://img-blog.csdnimg.cn/img_convert/079f17d273b64108486227fd3850f146.png
[6ec3259eb0400aa4b72d89145f6e3c3f.png]: https://img-blog.csdnimg.cn/img_convert/6ec3259eb0400aa4b72d89145f6e3c3f.png
[a033fc55dd265f62a816ea531a9be34b.png]: https://img-blog.csdnimg.cn/img_convert/a033fc55dd265f62a816ea531a9be34b.png