文件上传可以使用 Apache 文件上传组件, commons-fileupload, 它依赖于 commons-io
commons-io.jar： https://repo1.maven.org/maven2/commons-io/commons-io/2.6/commons-io-2.6.jar
commons-fileupload： https://repo1.maven.org/maven2/commons-fileupload/commons-fileupload/1.4/commons-fileupload-1.4.jar
maven地址
commons-iocommons-io2.6commons-fileuploadcommons-fileupload1.4代码package com.pro.servlet;import org.apache.commons.fileupload.FileItem;import org.apache.commons.fileupload.FileUploadException;import org.apache.commons.fileupload.ProgressListener;import org.apache.commons.fileupload.disk.DiskFileItemFactory;import org.apache.commons.fileupload.servlet.ServletFileUpload;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import java.io.*;import java.util.List;import java.util.UUID;public class UploadFileServlet02 extends HttpServlet {@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {System.out.println("UploadFileServlet02 POST");// 判断表单是普通表单还是带文件的表单if (!ServletFileUpload.isMultipartContent(req)) {return; // 终止方法}// 创建上传文件的保存路径, 建议在 WEN-INF 路径下, 安全且用户无法直接访问String uploadPath = this.getServletContext().getRealPath("/WEB-INF/upload");File uploadFile = new File(uploadPath);if (!uploadFile.exists()) {// 如果文件夹不存在, 就创建uploadFile.mkdir();}// 缓存, 临时文件, 假如文件超出了预期大小, 就放到临时文件中, 过几天删除, 或者转为永久文件String tempPath = this.getServletContext().getRealPath("/WEB-INF/temp");File tempFile = new File(tempPath);if (!tempFile.exists()) {// 如果文件夹不存在, 就创建uploadFile.mkdir();}// 处理文件上传, 一般通过获取流, request.getInputStream() 原生方式十分麻烦// 可以使用 Apache 文件上传组件, commons-fileupload, 它依赖于 commons-io 组件// 1. 创建 DiskFileItemFactory 对象, 处理文件上传路径或者大小限制DiskFileItemFactory factory = getDiskFileItemFactory(uploadFile);// 2. 获取 ServletFileUpload 对象负责处理上传文件数据, 可以监听文件上传进度, 以及编码问题ServletFileUpload upload = getServletFileUpload(factory);// 3. 处理上传文件String msg = uploadParamsRequest(upload, uploadPath, req);req.setAttribute("msg", msg);req.getRequestDispatcher("info.jsp").forward(req, resp);}// 获取 DiskFileItemFactory 对象, 处理文件上传路径或者大小限制public static DiskFileItemFactory getDiskFileItemFactory(File file) {// 处理文件上传, 一般通过获取流, request.getInputStream() 原生方式十分麻烦// 可以使用 Apache 文件上传组件, commons-fileupload, 它依赖于 commons-io 组件// 1. 创建 DiskFileItemFactory 对象, 处理文件上传路径或者大小限制DiskFileItemFactory factory = new DiskFileItemFactory();// 设置一个缓冲区大小, 当文件大于这个缓冲区大小的时候, 就会放到临时目录factory.setSizeThreshold(1024 * 1024); // 缓冲区大小 1 Mfactory.setRepository(file); // 设置临时目录, 接收一个 Filereturn factory;}// 获取 ServletFileUpload 对象负责处理上传文件数据, 可以监听文件上传进度, 以及编码问题public static ServletFileUpload getServletFileUpload(DiskFileItemFactory factory) {// 2. 获取 ServletFileUpload 对象负责处理上传文件数据, 可以监听文件上传进度, 以及编码问题ServletFileUpload upload = new ServletFileUpload(factory);// 监听文件上传进度upload.setProgressListener(new ProgressListener() {@Overridepublic void update(long readBytes, long contentLength, int i) {System.out.println("总大小: " + contentLength + " 已上传进度: " + readBytes);}});// 处理乱码问题upload.setHeaderEncoding("UTF-8");// 设置单个文件最大值upload.setFileSizeMax(1024 * 1024 * 10);// 设置总共能够上传文件大小upload.setFileSizeMax(1024 * 1024 * 10); // 10Mreturn upload;}// 保存文件public static String uploadParamsRequest(ServletFileUpload upload, String uploadPath, HttpServletRequest req) {String msg = "";try {// 3. 处理上传文件// 解析前段请求, 封装成一个 FileItem 对象, 需要从 ServletFileUpload 对象中获取List fileItems = upload.parseRequest(req);for (FileItem fileItem : fileItems) {// 判断上传文件是普通表单还是带文件的表单, true 代表普通表单, false 代表文件表单if (fileItem.isFormField()) {// 普通表单, 获取name属性String fieldName = fileItem.getFieldName();String value = fileItem.getString("UTF-8"); // 处理乱码System.out.println(fieldName + " : " + value);} else {//===================处理文件===================// 获取文件名String uploadFileName = fileItem.getName();System.out.println("上传的文件名: " + uploadFileName);// 判断文件名是否合法, 不合法直接跳过if (uploadFileName.trim().equals("") || uploadFileName == null) {continue;}// 获取上传的文件名String fileName = uploadFileName.substring(uploadFileName.lastIndexOf("/") + 1);// 获取上传文件后缀String uploadExtName = uploadFileName.substring(uploadFileName.lastIndexOf(".") + 1);System.out.println("文件信息 [文件名: " + fileName + " ---文件类型: " + uploadExtName + "]");// 网络传输中的东西需要 序列化(Serializable) 才能传输 Serializable: 标记接口, JVM --> Java栈 、 本地方法栈 native --> c++// 使用 UUID (唯一识别通用码), 保证文件名唯一UUID uuidPath = UUID.randomUUID();//===================存放地址===================// 文件真实存放的地址 readPathString readPath = uploadPath + File.separator + uuidPath;// 给文件开辟一个文件夹File readPathFile = new File(readPath);if (!readPathFile.exists()) {// 如果没有该文件夹, 就创建readPathFile.mkdir();}//===================文件传输===================// 获取输入流InputStream is = fileItem.getInputStream();// 获取文件输出流FileOutputStream fos = new FileOutputStream(readPathFile + File.separator + fileName);// 建立缓存区byte[] buffer = new byte[1024 * 1024];int len = 0;// 读取流while ((len = is.read(buffer)) > 0) {fos.write(buffer, 0, len);}// 关闭流fos.close();is.close();// 清除临时文件fileItem.delete();}}msg = "文件上传成功";} catch (Exception e) {e.printStackTrace();msg = "文件上传失败";}return msg;}}