commons-fileupload+servlet实现简单文件上传

来源：互联网发布：中国核弹数量知乎编辑：程序博客网时间：2024/06/06 02:48

这两天复习servlet，做文件上传，刚开始是这样写的

public class FileUploadServlet extends HttpServlet{    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        req.setCharacterEncoding("utf-8");        InputStream is = req.getInputStream();        String path = getServletContext().getRealPath("/uploads/a.jpg");        System.out.println(path);        File file = new File(path);        file.createNewFile();        FileOutputStream fos = new FileOutputStream(file);        byte[] b = new byte[1024];        int n=0;        while((n=is.read(b))!=-1){           fos.write(b,0,n);        }                fos.close();        is.close();    }}

发现上传图片等非文本文件是不能打开的，并且得到的文件比源文件要大，然后就想到用commons-fileupload来做上传，先上代码。

public class RegisterServlet extends HttpServlet {    @Override    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {        //req.setCharacterEncoding("utf-8");已无用        DiskFileItemFactory factory = new DiskFileItemFactory();<span style="white-space:pre">//设置阀值        factory.setSizeThreshold(1024);</span>        ServletContext context = getServletContext();        //获取上传路径        String dir = context.getInitParameter("uploadDir");        ServletFileUpload upload = new ServletFileUpload(factory);                try {            List<FileItem> items = upload.parseRequest(req);            Iterator<FileItem> iter = items.iterator();            while (iter.hasNext()) {                FileItem item = iter.next();                //如果是普通的项                if (item.isFormField()) {                    System.out.println(item.getFieldName());                    //获取utf-8格式的值                    System.out.println(item.getString("utf-8"));                }                //如果是文件项                else {                    System.out.println(item.getFieldName());                    InputStream is = item.getInputStream();                    String path = getServletContext().getRealPath(dir);                    //获取源文件的名字                    File file = new File(path,item.getName());                    if(!file.exists()){                        file.createNewFile();                    }                    OutputStream os = new FileOutputStream(file);                    int bytesRead = 0;                    byte[] buffer = new byte[1024];                    while((bytesRead = is.read(buffer, 0, 1024)) != -1){                        os.write(buffer, 0, bytesRead);                    }                    os.close();                    is.close();                }            }        } catch (FileUploadException e) {            e.printStackTrace();        }            }    /**     * @param item     */    private void processUploadedFile(FileItem item) {            }    /**     * @param item     */    private void processFormField(FileItem item) {            }

简单看一下源码，commons-fileupload组件是对rfc1867协议(有兴趣的可以看一下)的java实现与扩展,。

当上传文件时会有一个阀值(threshold)，低于阀值时文件保存在内存中，高于阀值会写在临时文件里，临时文件的路径由组件指定，,对于大文件上传这样可以节省内存，保存好之后，才是我们得到输入流来写入指定路径文件。

0 0