javaweb 文件上传(fileupload) 下载

来源：互联网发布：truelicense源码包编辑：程序博客网时间：2024/06/15 04:27

1 文件上传

html中通过<input type="file"/>可以向服务器上传文件。不过后台需要手动解析请求，比较复杂，所以可以使用smartupload或apache的fileupload组件进行文件的上传。smartupload据网友测试，在上传大文件时不稳定，所以还是使用fileupload的吧，毕竟apache出品。

本例子中使用的jar包:

commons-fileupload-1.3.2.jar
commons-io-2.5.jar（fileupload依赖）

前端jsp页面:

    <div class="upload">        <form action="UploadFileServlet" method="POST" enctype="multipart/form-data">            上传文件:<input type="file" name="uploadFile">        <input type="submit" value="upload">上传        <input type="reset" value="reset">重置        </form>    </div>

其中有几个需要注意的点:

form表单的enctype必须为"multipart/form-data"。
<input type="file" name="uploadFile"/> 中必须有name属性，因为在fileupload中会根据fieldName解析上传的文件。
method必须为POST方法。
如果多文件上传的话，file类型的name必须为不同的名称。

服务端需要建立一个UploadFileServlet来处理请求。
关键的doPost方法:

protected void doPost(HttpServletRequest request,            HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        // 首先检测是否是文件上传，主要依据enctype的值来判定        if (!ServletFileUpload.isMultipartContent(request)) {            PrintWriter writer = response.getWriter();            writer.write("Error 不是文件上传,表单必须包含 enctype='multipart/form-data'");            writer.flush();            writer.close();            return;        }        DiskFileItemFactory factory = new DiskFileItemFactory();        // 设置在内存中的缓存大小，如果超过了则保存到临时文件。        factory.setSizeThreshold(MEMORY_THRESHOLD);        System.err.println(System.getProperty("java.io.tmpdir"));        // 设置临时文件夹的目录        factory.setRepository(new File(System.getProperty("java.io.tmpdir")));        ServletFileUpload upload = new ServletFileUpload(factory);        // 设置单个文件大小的最大值        upload.setFileSizeMax(MAX_FILE_SIZE);        // 设置上传文件总量的最大值，包括所有文件和表单的总和        upload.setSizeMax(MAX_REQUEST_SIZE);        File uploadDir = new File(UPLOAD_PATH);        if (!uploadDir.exists()) {            uploadDir.mkdir();        }        try {            // 解析request            List<FileItem> formItems = upload.parseRequest(request);            if (formItems != null && formItems.size() > 0) {                for (FileItem item : formItems) {                    // 如果不是普通的formField则就是上传的文件                    if (!item.isFormField()) {                        String fileName = item.getName();                        File storeFile = new File(UPLOAD_PATH + File.separator                                + fileName);                        System.err.println(storeFile.getAbsolutePath());                        item.write(storeFile);                        item.delete();                    } else {                        System.err.println(item.getString());                    }                }            }            request.setAttribute("message", "成功");            request.getRequestDispatcher("result.jsp").forward(request,                    response);        } catch (Exception e) {            // TODO: handle exception            request.setAttribute("message", e.getMessage());            request.getRequestDispatcher("result.jsp").forward(request,                    response);            e.printStackTrace();            return;        }    }

这样即可实现文件的上传。

需要改进的地方

没有上传进度
限制文件大小
限制文件类型

对于第2点，可以利用fileupload的抛出异常解决。

catch(FileUploadBase.FileSizeLimitExceededException e){            request.setAttribute("message", "单个文件大小超过限制");            request.getRequestDispatcher("result.jsp").forward(request,                    response);            e.printStackTrace();            return;        } catch(FileUploadBase.SizeLimitExceededException e){            request.setAttribute("message", "上传文件总大小超过限制");            request.getRequestDispatcher("result.jsp").forward(request,                    response);            e.printStackTrace();            return;        }

对于第3点，可以在页面用js进行校验。

    <form action="UploadFileServlet" method="POST"        enctype="multipart/form-data" onsubmit="return check_file()">        上传文件:<input type="file" name="uploadFile" id="uploadFile"> <input            type="submit" value="upload">上传 <input type="reset"            value="reset">重置    </form>    <script>        function check_file() {            var fileName = document.getElementById("uploadFile").value;            var suffix = fileName.substr(fileName.lastIndexOf(".") + 1);            if (suffix !== "exe") {                alert("只能上传exe文件");                return false;            }        }    </script>

对于第1点，fileupload可以添加监听器，监听上传进度。

//设置上传进度的监听器        ProgressListener progressListener = new ProgressListener() {            public void update(long pBytesRead, long pContentLength, int pItems) {                System.out.println("We are currently reading item " + pItems);                if (pContentLength == -1) {                    System.out.println("So far, " + pBytesRead                            + " bytes have been read.");                } else {                    System.out.println("So far, " + pBytesRead + " of "                            + pContentLength + " bytes have been read.");                    uploadPercent = (double) pBytesRead / pContentLength;                    System.err.println(uploadPercent);                }            }        };        upload.setProgressListener(progressListener);

虽然服务端添加了监听器，可以在console或者Log里打印上传进度，但我们想要的是让用户看到上传进度。所以需要把进度返回给用户。
要解决的问题主要有两个：

进度信息如何保存
前台如何获取
其中的一种方案是利用session。我们将上传进度保存在session里，前台通过ajax方法定时获取上传的进度，因为每个用户是一个session,不同的用户session不同。这样当不同的用户同时上传文件时，依然可以正确的获得上传进
度，不会获取到其他用户上传文件的进度。
具体首先有一个简单的保存上传进度的实体类:
```
public class UploadStatus {private double percent;public double getPercent() {    return percent;}public void setPercent(double percent) {    this.percent = percent;}}
```
然后有一个监听的类，实现了ProgressListener接口

public class UploadListener implements ProgressListener{    private UploadStatus status;    public  UploadListener(UploadStatus status) {        // TODO Auto-generated constructor stub        this.status = status;    }    @Override    public void update(long pBytesRead, long pContentLength, int pItems) {        // TODO Auto-generated method stub        double uploadPercent = (double) pBytesRead / pContentLength;        status.setPercent(uploadPercent);    }}

在doPost方法中:

//设置上传进度的监听器        UploadStatus status = new UploadStatus();        UploadListener listener = new UploadListener(status);        upload.setProgressListener(listener);        request.getSession(true).setAttribute("uploadStatus", status);

最后在doGet方法中，返回上传进度。

protected void doGet(HttpServletRequest request,            HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        response.setContentType("text/html");        response.setCharacterEncoding("UTF-8");        response.setHeader("Cache-Control", "no-store");        response.setDateHeader("Expires", 0);        response.setHeader("Pragrma", "no-cache");        PrintWriter writer = response.getWriter();        UploadStatus status = (UploadStatus)(request.getSession().getAttribute("uploadStatus"));        if(status != null){            writer.write("上传进度:" + status.getPercent());        }else{            writer.write("没有上传信息");        }        writer.flush();        writer.close();    }

当用户上传时可以访问doGet方法即可获取进度。
前台页面可以这样写:
其中form的target属性可以防止页面跳转。

<body><iframe width=0 height=0 name="uploadFrame"></iframe>    <form action="UploadFileServlet" method="POST"        enctype="multipart/form-data" target="uploadFrame" onsubmit="getStatus()">        上传文件:<input type="file" name="uploadFile" id="uploadFile"> <input            type="submit" value="upload">上传 <input type="reset"            value="reset">重置    </form>    <span>上传进度:</span><span id="progress"></span>    <script src="jquery-1.11.2.js"></script>    <script>    var finished ;        function check_file() {            var fileName = document.getElementById("uploadFile").value;            var suffix = fileName.substr(fileName.lastIndexOf(".") + 1);            if (suffix !== "exe") {                //alert("只能上传exe文件");                //return false;            }            finished = false;            return true;        }        function getStatus(){            finished = false;            console.log("finished = " + finished)            showStatus();        }        function showStatus(){            console.log("showstatus finished = " + finished)            if(finished === true) return;            $.ajax({                url:'UploadFileServlet',                type:'GET',                success:function(data){                    $('#progress').text(data);                    if(data == '1.0'){                        finished = true;                    }                },                error:function(data){                    alert(data);                }            });            setTimeout(showStatus,1000);        }    </script></body>

最后完整的程序UploadFile.zip

2 文件下载

文件下载相对比较简单

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {        // TODO Auto-generated method stub        String id = request.getParameter("id");        //app.properties 路径        DFileItem dao = new DFileItem();        String basePath = request.getSession().getServletContext().getRealPath("");        String configPath = basePath+Constants.CONFIG_PATH;        String uploadPath = Configuration.getInstance(configPath).getProperty(Constants.FILE_STORAGE_PATH);        FileItem item = dao.queryFileItem(id);        if(item == null){            PrintWriter writer = response.getWriter();            writer.write("文件已经被删除");            writer.close();            return;        }        String name = item.getFileName();        response.setContentType("application/octet-stream");        String downloadName = URLEncoder.encode(name,"UTF-8").replaceAll("\\+", "%20");        response.setHeader("Content-Disposition", "attachment;filename*=utf-8'zh_cn'"+downloadName);        File file = new File(uploadPath+item.getUploadTime());        response.setContentLength((int)file.length());        FileInputStream in = new FileInputStream(file);        OutputStream out = response.getOutputStream();        byte[] buffer = new byte[8192];        int len = 0;        while((len = in.read(buffer)) != -1){            out.write(buffer, 0, len);        }        out.flush();        out.close();        in.close();    }

注意response 的contentType和header的设置即可。

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