Java Web Servlet 上传和下载文件

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：

fileupload.jspallfiles.jspfileuploadResponse.jspUploadDetail.javaFileUploadServlet.javaUploadedFileServlet.javaFileDownloadServlet.javaweb.xmlmain.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"%>


    
        
        Servlet File Upload/Download
        
                
                    Upload File: 
                    Please Upload A File!
                
                
            
        

        
        
            /uploadedFilesServlet">List all uploaded files

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"%>


    
        
        Servlet File Upload/Download

        
                
                    File NameFile SizeAction
                
                
                    <% List uploadDetails = (List) request.getAttribute("uploadedFiles");
                        if (uploadDetails != null && uploadDetails.size() > 0) {
                            for (int i = 0; i < uploadDetails.size(); i++) {
                    %>
                    
                        <%=uploadDetails.get(i).getFileName()%>
                        <%=uploadDetails.get(i).getFileSize()%> KB
                        /downloadServlet?fileName=<%=uploadDetails.get(i).getFileName()%>">Download
                    
                    <% }
                  } else { %>
                    
                        No Files Uploaded.....!
                    
                    <% }%>
                
            
            
                /fileupload.jsp">Back

fileuploadResponse.jsp

<%@page import="java.util.List"%>
<%@page import="com.servlet.UploadDetail"%>
<%@page language="java" contentType="text/html; charset=UTF-8" pageEncoding="UTF-8"%>


    
        
        Servlet File Upload/Download

        
                
                    File NameFile SizeUpload StatusAction
                
                
                    <% List uploadDetails = (List) request.getAttribute("uploadedFiles");
                        for (int i = 0; i < uploadDetails.size(); i++) {
                    %>
                    
                        <%=uploadDetails.get(i).getFileName()%>
                        <%=uploadDetails.get(i).getFileSize()%> KB
                        <%=uploadDetails.get(i).getUploadStatus()%>
                        /downloadServlet?fileName=<%=uploadDetails.get(i).getFileName()%>">Download
                    
                    <% }%>
                
            
            
                /fileupload.jsp">Back

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";

    
    public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleRequest(request, response);
    }

    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        
        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 fileList = new ArrayList();

        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);
    }

    
    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";

    
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleRequest(request, response);
    }

    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        
        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 fileList = new ArrayList();

        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";

    
    public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        handleRequest(request, response);
    }

    public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        
        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()) {

            
            String mimeType = "application/octet-stream";
            response.setContentType(mimeType);

            
            String headerKey = "Content-Disposition";
            String headerValue = String.format("attachment; filename="%s"", file.getName());
            response.setHeader(headerKey, headerValue);

            try {

                
                outStream = response.getOutputStream();
                inputStream = new FileInputStream(file);
                byte[] buffer = new byte[BUFFER_SIZE];
                int bytesRead = -1;

                
                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 {

            
            response.setContentType("text/html");

            
            response.getWriter().println("File " + fileName + " Is Not Present .....!");
        }
    }
}

web.xml



    Servlet File Upload/Download
    
        fileupload.jsp

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。

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。

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。

下载特定文件后，您将在此 PC -> 下载选项中找到该文件。

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。

Java Web Servlet 上传和下载文件

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