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="/UploadFiles/2021-04-02/jquery.min.js">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"htmlcode"><"1.0" encoding="UTF-8""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。