JavaServlet的文件上传和下载实现方法

作者：袖梨 2025-07-04
下面小编就为大家分享一篇JavaServlet的文件上传和下载实现方法具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧

先分析一下上传文件的流程

1-先通过前段页面中的选择文件选择要上传的图片

index.jsp

<%@ page language="java" import="java.util.*" pageEncoding="utf-8" contentType="text/html; charset=UTF-8"%><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"><html> <head><title>My JSP 'index.jsp' starting page</title><meta http-equiv="content-type" content="text/html;charset=utf-8"><meta http-equiv="pragma" content="no-cache"><meta http-equiv="cache-control" content="no-cache"><meta http-equiv="expires" content="0"><meta http-equiv="keywords" content="keyword1,keyword2,keyword3"><meta http-equiv="description" content="This is my page"><script type="text/javascript" src="js/jquery.min.js"></script><script type="text/javascript" src="js/common.js"></script><script type="text/javascript" src="js/ajaxfileupload.js"></script> </head> <body><input type="file" value="上传" name="inputImage" id="inputImage"><input type="button" value="上传" id="upload"><a id="downLoad">下载</a> </body></html>

2-点击提交按钮，通过ajax的文件上传访问服务器端

common.js　　

var path = (function() { //获取当前网址 var curWwwPath = window.document.location.href; //获取主机地址之后的目录 var pathName = window.document.location.pathname; var pos = curWwwPath.indexOf(pathName); //获取主机地址 var localhostPath = curWwwPath.substring(0, pos); //获取带"/"的项目名 var projectName = pathName.substring(0, pathName.substr(1).indexOf('/') + 1); return { curWwwPath: curWwwPath, pathName: pathName, localhostPath: localhostPath, projectName: projectName, //部署路径 deployPath: localhostPath + projectName};})();
// 文件下载$("a[id=downLoad]").click(function(){ window.location.href=path.deployPath+"/fileDown";});// 文件上传$("input[id=upload]").click(function() { $.ajaxFileUpload( {url : path.deployPath + "/fileUp", // 处理页面的绝对路径fileElementId : "inputImage", //file空间的id属性dataType : "json",success : function(data) { alert("上传成功");} });});

3-服务器端响应保存或者下载

保存上传文件的FileUpload.java

import java.io.File;import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import java.util.List;import java.util.UUID;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import net.sf.json.JSONArray;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 com.stu.util.HttpUtil;/** * 文件名称： com.stu.fileupload.FileUpload.java<br/> * 初始作者： Administrator<br/> * 创建日期： 2018-1-31<br/> * 功能说明： 文件上传 <br/> * =================================================<br/> * 修改记录：<br/> * 修改作者 日期 修改内容<br/> * ================================================<br/> * Copyright (c) 2010-2011 .All rights reserved.<br/> */public class FileUpload extends HttpServlet { private static final long serialVersionUID = 1L; @Override protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {// 获取到当前服务器所在的路径String serverPath = req.getSession().getServletContext().getRealPath("/");// 设置保存上传文件的路径String saveDirPath = serverPath + "img";File saveDirPathFileObj = new File(saveDirPath);// 如果当用来存放文件的目录不存在时，要创建该目录if (!saveDirPathFileObj.exists()) { saveDirPathFileObj.mkdirs();}// 创建一个解析器工厂DiskFileItemFactory factory = new DiskFileItemFactory();// 设置工厂的缓存区大小factory.setSizeThreshold(5 * 1024);// 文件上传的解析器(文件上传对象)ServletFileUpload upload = new ServletFileUpload(factory);// 设置上传文件的最大值upload.setSizeMax(3 * 1024 * 1024);// 设置编码格式upload.setHeaderEncoding("UTF-8");try { // 上传以后的文件名 List<String> uploadFileNames = new ArrayList<String>(); List<FileItem> fileItems = upload.parseRequest(req); System.out.println(fileItems); for (FileItem file : fileItems) {// 新的文件名String saveFileName = UUID.randomUUID().toString().replace("-", "");// 文件的后缀String oldFileName = new String(file.getName().getBytes(),"UTF-8");System.out.println("oldFileName" + oldFileName);String fileType = oldFileName.substring(oldFileName.lastIndexOf("."));// 新的文件路径String saveFilePath = saveDirPath + File.separator+ saveFileName + fileType;uploadFileNames.add(saveFileName + fileType);// 保存上传的文件file.write(new File(saveFilePath)); } System.out.println(uploadFileNames); HttpUtil.setAttribute(req, "urls", uploadFileNames); res.setContentType("application/json;charset=utf-8"); PrintWriter pw = res.getWriter(); pw.print(JSONArray.fromObject(uploadFileNames));} catch (FileUploadException e) { e.printStackTrace();} catch (Exception e) { e.printStackTrace();} }}

下载文件的FileDownload.java

import java.io.File;import java.io.IOException;import java.io.PrintWriter;import java.util.ArrayList;import java.util.List;import java.util.UUID;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import net.sf.json.JSONArray;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 com.stu.util.HttpUtil;/** * 文件名称： com.stu.fileupload.FileUpload.java<br/> * 初始作者： Administrator<br/> * 创建日期： 2018-1-31<br/> * 功能说明： 文件上传 <br/> * =================================================<br/> * 修改记录：<br/> * 修改作者 日期 修改内容<br/> * ================================================<br/> * Copyright (c) 2010-2011 .All rights reserved.<br/> */public class FileUpload extends HttpServlet { private static final long serialVersionUID = 1L; @Override protected void service(HttpServletRequest req, HttpServletResponse res) throws ServletException, IOException {// 获取到当前服务器所在的路径String serverPath = req.getSession().getServletContext().getRealPath("/");// 设置保存上传文件的路径String saveDirPath = serverPath + "img";File saveDirPathFileObj = new File(saveDirPath);// 如果当用来存放文件的目录不存在时，要创建该目录if (!saveDirPathFileObj.exists()) { saveDirPathFileObj.mkdirs();}// 创建一个解析器工厂DiskFileItemFactory factory = new DiskFileItemFactory();// 设置工厂的缓存区大小factory.setSizeThreshold(5 * 1024);// 文件上传的解析器(文件上传对象)ServletFileUpload upload = new ServletFileUpload(factory);// 设置上传文件的最大值upload.setSizeMax(3 * 1024 * 1024);// 设置编码格式upload.setHeaderEncoding("UTF-8");try { // 上传以后的文件名 List<String> uploadFileNames = new ArrayList<String>(); List<FileItem> fileItems = upload.parseRequest(req); System.out.println(fileItems); for (FileItem file : fileItems) {// 新的文件名String saveFileName = UUID.randomUUID().toString().replace("-", "");// 文件的后缀String oldFileName = new String(file.getName().getBytes(),"UTF-8");System.out.println("oldFileName" + oldFileName);String fileType = oldFileName.substring(oldFileName.lastIndexOf("."));// 新的文件路径String saveFilePath = saveDirPath + File.separator+ saveFileName + fileType;uploadFileNames.add(saveFileName + fileType);// 保存上传的文件file.write(new File(saveFilePath)); } System.out.println(uploadFileNames); HttpUtil.setAttribute(req, "urls", uploadFileNames); res.setContentType("application/json;charset=utf-8"); PrintWriter pw = res.getWriter(); pw.print(JSONArray.fromObject(uploadFileNames));} catch (FileUploadException e) { e.printStackTrace();} catch (Exception e) { e.printStackTrace();} }}

这里面用到了一个HttpUtil类，代码如下：

import javax.servlet.FilterConfig;import javax.servlet.ServletConfig;import javax.servlet.ServletContext;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpSession;/** * 文件名称＿com.niit.model2.util.Httputil.java</br> * 初始作逯ܿAdministrator</br> * 创建日期＿2018-1-23</br> * 功能说明＿这里用一句话描述这个类的作用--此句话需删除 <br/> * =================================================<br/> * 修改记录＿br/> * 修改作迠日期 修改内容<br/> * ================================================<br/> * Copyright (c) 2010-2011 .All rights reserved.<br/> */public class HttpUtil {private HttpUtil() {}/** * 方法描述: [用于向不同的作用域存放属性]</br> * 初始作迺 Administrator<br/> * 创建日期: 2018-1-23-上午11:24:45<br/> * 弿Nj版本: 2.0.0<br/> * =================================================<br/> * 修改记录＿br/> * 修改作迠日期 修改内容<br/> * ================================================<br/> * void */public static void setAttribute(Object scopeObj, String name, Object value) {if (scopeObj instanceof HttpServletRequest) {((HttpServletRequest) scopeObj).setAttribute(name, value);}if (scopeObj instanceof HttpSession) {((HttpSession) scopeObj).setAttribute(name, value);}if (scopeObj instanceof ServletContext) {((ServletContext) scopeObj).setAttribute(name, value);}}/** * 方法描述: [获取作用域中指定名称的属性思</br> * 初始作迺 Administrator<br/> * 创建日期: 2018-1-23-上午11:29:17<br/> * 弿Nj版本: 2.0.0<br/> * =================================================<br/> * 修改记录＿br/> * 修改作迠日期 修改内容<br/> * ================================================<br/> ** @param scopeObj * @param name * @return * Object */public static Object getAttribute(Object scopeObj, String name) {if (scopeObj instanceof HttpServletRequest) {return ((HttpServletRequest) scopeObj).getAttribute(name);}if (scopeObj instanceof HttpSession) {return ((HttpSession) scopeObj).getAttribute(name);}if (scopeObj instanceof ServletContext) {return ((ServletContext) scopeObj).getAttribute(name);}return null;}/** * 方法描述: [获取上下文对象的方法]</br> * 初始作迺 Administrator<br/> * 创建日期: 2018-1-23-上午11:31:26<br/> * 弿Nj版本: 2.0.0<br/> * =================================================<br/> * 修改记录＿br/> * 修改作迠日期 修改内容<br/> * ================================================<br/> ** @return * ServletContext */public static ServletContext getServletContext(Object sourceObj) {if (sourceObj instanceof HttpServletRequest) {return ((HttpServletRequest) sourceObj).getSession().getServletContext();}if (sourceObj instanceof ServletConfig) {return ((ServletConfig) sourceObj).getServletContext();}if (sourceObj instanceof FilterConfig) {return ((FilterConfig) sourceObj).getServletContext();}return null;}/** * 方法描述: [获取项目的实际路径]</br> * 初始作迺 Administrator<br/> * 创建日期: 2018-1-23-上午11:45:47<br/> * 弿Nj版本: 2.0.0<br/> * =================================================<br/> * 修改记录＿br/> * 修改作迠日期 修改内容<br/> * ================================================<br/> ** @param req * @return * String */public static String getContextPath(HttpServletRequest req) {return req.getContextPath();}}

当然，代码编辑好了也不要忘了在 WebRoot/WEB-INF/web.xml 中添加新建的Servlet，就是刚刚的两个Java文件啦

<?xml version="1.0" encoding="UTF-8"?><web-app version="2.5" 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_2_5.xsd"><welcome-file-list><welcome-file>index.jsp</welcome-file></welcome-file-list><!-- 文件上传 --><servlet><servlet-name>fileUpload</servlet-name><servlet-class>com.stu.fileupload.FileUpload</servlet-class></servlet><servlet-mapping><servlet-name>fileUpload</servlet-name><url-pattern>/fileUp</url-pattern></servlet-mapping><!-- 文件下载 --><servlet><servlet-name>fileDownload</servlet-name><servlet-class>com.stu.fileupload.FileDownload</servlet-class></servlet><servlet-mapping><servlet-name>fileDownload</servlet-name><url-pattern>/fileDown</url-pattern></servlet-mapping></web-app>

这样的话就可以运行啦。

TIP： 不要忘记相关的jar包和 js 包哦

在 WebRoot / WEB-INF / lib 下，有 commons-fileupload.jar 和 commons-io.jar ，另外 json-lib-x.x.x-jdkxx.jar 包是用来把上传的返回数据修改为JSON格式的

在 WebRoot / js 下，导入 jquery.js , common.js , ajaxfileupload.js

以上这篇JavaServlet的文件上传和下载实现方法就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持一聚教程网。

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