说明

在实现上传文件时，需要限制文件大小，否则上传 大文件 ，会给服务器带来巨大负担

通过 ServletFileUpload类对象实现：

• setFileSizeMax(); ：设置最大上传文件的大小

• setSizeMax()：设置最大请求的大小

实现

关键代码

// 设置最大文件大小，超过会报错
sfu.setFileSizeMax(MAX_FILE_SIZE);
// 设置最大请求值 (包含文件和表单数据)
sfu.setSizeMax(MAX_REQUEST_SIZE);

完整代码

@WebServlet(urlPatterns ="/upload")
public class UploadServlet extends HttpServlet {

    // 上传文件存储目录
    private static final String UPLOAD_PATH = "upload";

    // 上传配置
    private static final int MAX_FILE_SIZE      = 1024 * 1024 * 5; // 5MB
    private static final int MAX_REQUEST_SIZE   = 1024 * 1024 * 6; // 6MB

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        boolean isMC=ServletFileUpload.isMultipartContent(req);
        if(isMC){
            FileItemFactory fif=new DiskFileItemFactory();
            ServletFileUpload sfu=new ServletFileUpload(fif);

            // 设置最大文件大小，超过会报错
            //一般都会设置文件大小，否则上传1G文件，服务器承受不了
            sfu.setFileSizeMax(MAX_FILE_SIZE);
            // 设置最大请求值 (包含文件和表单数据)
            sfu.setSizeMax(MAX_REQUEST_SIZE);

            // 构造保存上传文件的路径
            String uploadPath = getServletContext().getRealPath("/"+UPLOAD_PATH) ;
            File uploadPathFile=new File(uploadPath);
            if(!uploadPathFile.exists()){
                uploadPathFile.mkdirs();
            }
            try {
                Map<String, List<FileItem>> map=sfu.parseParameterMap(req);
                List<FileItem> imgs=map.get("img");
                List<FileItem> descrips=map.get("descrip");

                if(imgs!=null && !imgs.isEmpty()){
                    FileItem img=imgs.get(0);
                    File uploadFile=new File(uploadPathFile, img.getName());
                    img.write(uploadFile);
                }

                if(descrips!=null && !descrips.isEmpty()){
                    String descrip=descrips.get(0).getString("utf-8");
                    System.out.println(descrip);
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

        }
    }
}

上传超过大小的文件，报错如下：

org.apache.commons.fileupload.FileUploadBase$SizeLimitExceededException: the request was rejected because its size (14452145) exceeds the configured maximum (6291456)