文件上传

1. 导入jar包，这里还要导入servlet api

2. 编写servlet

@WebServlet("/upFile")
public class UpLoad extends HttpServlet {

    // 上传文件存储目录
    private static final String UPLOAD_DIRECTORY = "upload";
    // 上传配置
    // 3MB
    private static final int MEMORY_THRESHOLD   = 1024 * 1024 * 3;
    // 40MB
    private static final int MAX_FILE_SIZE      = 1024 * 1024 * 40;
    // 50MB
    private static final int MAX_REQUEST_SIZE   = 1024 * 1024 * 50;

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        if(!ServletFileUpload.isMultipartContent(req)){
            /**
             * 可以添加提示信息
             */
            return;
        }
        ServletFileUpload upload = this.getUpload();
        this.upload(upload);
        // 构造临时路径来存储上传的文件
        // 这个路径相对当前应用的目录
        String uploadPath = req.getServletContext().getRealPath("./") + File.separator + UPLOAD_DIRECTORY;
        File filePath = new File(uploadPath);
        if(!filePath.exists()){
            filePath.mkdirs();
        }

        try {
            List<FileItem> formItems = upload.parseRequest(req);
            if(formItems!=null&&formItems.size()>0){
                for (FileItem item : formItems) {
                    System.out.println("item.getName()::"+item.getName());
                    //String fileName = new File(item.getName()).getName();
                    if (!item.isFormField()) {
                        String fileName = new File(item.getName()).getName();
                        String path = uploadPath + File.separator + fileName;
                        File storeFile = new File(path);
                        // 在控制台输出文件的上传路径
                        System.out.println(filePath);
                        // 保存文件到硬盘
                        item.write(storeFile);
                        req.setAttribute("message","文件上传成功!");
                    }
                }
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    //获取ServletFileUpload
    public ServletFileUpload getUpload(){
        // 配置上传参数
        DiskFileItemFactory factory = new DiskFileItemFactory();
        // 设置内存临界值 - 超过后将产生临时文件并存储于临时目录中
        factory.setSizeThreshold(MEMORY_THRESHOLD);
        // 设置临时存储目录
        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));
        ServletFileUpload upload = new ServletFileUpload(factory);
        return upload;
    }

    public void upload(ServletFileUpload upload){
        // 设置最大文件上传值
        upload.setFileSizeMax(MAX_FILE_SIZE);
        // 设置最大请求值 (包含文件和表单数据)
        upload.setSizeMax(MAX_REQUEST_SIZE);
        // 中文处理
        upload.setHeaderEncoding("UTF-8");
    }
}

3. 前台代码

form的method必须设置为post 必须添加enctype属性，这样form表单会把数据以二进制的形式传输

<body>
  <form action="${pageContext.request.contextPath}/upFile" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="提交">
  </form>
  </body>