Java文件传输和上传

Meow Mii

2023-02-12 (Updated: 2023-02-12)

Java

用到的包：common-io、common-fileload

文件上传调优（注意事项）：

为保证服务器安全，上传的文件应该放在外界无法直接访问的目录下，比如说WEB-INF目录下
为防止文件覆盖的现象发生，要为上传的文件产生唯一的文件名
要限制上传文件的最大值
可以限制文件的类型，在收到文件名时，判断后缀名是否合法
ServletFileUpload负责处理上传的文件数据，并将表单中每个输入项封装成一个FileItem对象，在使用ServletFileUpload对象解析请求时需要DiskFileItemFactory对象。所以我们需要在进行解析工作前构造好DiskFileItemFactory对象，通过ServletFileUpload对象的构造方法或setFileItemFactory()方法设置ServletFileUpload对象的fileItemFactory属性。

流程

页面必须包含一个type为file的表单

method必须为post因为get限制了大小

ddfa.jsp

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>test</title>
</head>
<body>
<form action="${pageContext.request.contextPath}/upload.do" method="post" enctype="multipart/form-data">
    <p>上传用户：<input type="text" name="username"></p>
    <p><input type="file" name="file"></p>
    <p>
        <input type="submit">|<input type="reset">
    </p>
</form>
</body>
</html>

index.jsp(success.jsp)

<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <meta charset="utf-8">
    <title>FileUpload</title>
    <meta name="renderer" content="webkit">
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
    <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1">
    <link rel="stylesheet" href="/css/layui.css" tppabs="/css/layui.css"  media="all">
    <!-- 注意：如果你直接复制所有代码到本地，上述css路径需要改成你本地的 -->
    
    
</head>
<body>
<p>${msg}</p>
    
    
   <!-- 后续页面美化可以使用layui实现 -->
<fieldset class="layui-elem-field layui-field-title" style="margin-top: 30px;">
    <legend>拖拽上传</legend>
</fieldset>

<div class="layui-upload-drag" id="test10">
    <i class="layui-icon"></i>
    <p>点击上传，或将文件拖拽到此处</p>
    <div class="layui-hide" id="uploadDemoView">
        <hr>
        <img src="" alt="上传成功后渲染" style="max-width: 196px">
    </div>
</div>


<script src="/js/layui.js" charset="utf-8"></script>
<!-- 注意：如果你直接复制所有代码到本地，上述 JS 路径需要改成你本地的 -->
<script>
    layui.use(['upload', 'element', 'layer'], function(){
        var $ = layui.jquery
            ,upload = layui.upload
            ,element = layui.element
            ,layer = layui.layer;


        //拖拽上传
        upload.render({
            elem: '#test10'
            ,url: '${pageContext.request.contextPath}/upload.do' //此处用的是第三方的 http 请求演示，实际使用时改成您自己的上传接口即可。
            ,done: function(res){
                layer.msg('上传成功');
                layui.$('#uploadDemoView').removeClass('layui-hide').find('img').attr('src', res.files.file);
                console.log(res)
            }
        });
    });
</script>

</body>
</html>

FileUploadController：doPost

@Override
   protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
       // 判断表单是否包含文件上传控件
       if (!ServletFileUpload.isMultipartContent(req)){
           // 不包含文件上传控件，即普通表单
           return;
       }

       //创建文件保存路径，外界无法访问
       String uploadPath = this.getServletContext().getRealPath("/WEB-INF/upload");
       File uploadFile = new File(uploadPath);
       makeIfNotExists(uploadFile);

       //创建临时文件保存路径
       String tmpPath = this.getServletContext().getRealPath("/WEB-INF/tmp");
       File tmpFile = new File(tmpPath);
       makeIfNotExists(tmpFile);

       // 1.创建DiskFileItemFactory对象
       DiskFileItemFactory factory = getDiskFileItemFactory(tmpFile);
       // 2.创建ServletFileUpload对象
       ServletFileUpload servletFileUpload = getServletFileUpload(factory);
       // 3.解析请求并处理文件传输
       String msg ="";
       try {
           msg = uploadParseRequest(req,servletFileUpload,uploadPath);
       } catch (FileUploadException e) {
           e.printStackTrace();
       }

       req.setAttribute("msg",msg);
       req.getRequestDispatcher("/index.jsp").forward(req,resp);
   }

getDiskFileItemFactory：

/**
     * 获得文件项目工程，设置缓冲文件夹以及缓冲区大小
     * @param tmpFile 缓冲文件夹
     * @return
     */
    private DiskFileItemFactory getDiskFileItemFactory(File tmpFile){
        DiskFileItemFactory factory = new DiskFileItemFactory();
        factory.setSizeThreshold(1024*1024);//超出缓冲区使用临时文件缓存上传
        factory.setRepository(tmpFile);//临时文件夹

getSercletFileUpload：

private ServletFileUpload getServletFileUpload(DiskFileItemFactory factory){
      ServletFileUpload servletFileUpload = new ServletFileUpload();
      servletFileUpload.setFileItemFactory(factory);

      // 辅助功能
      //监听文件上传进度
      servletFileUpload.setProgressListener(new ProgressListener() {
          @Override
          //已读文件大小 文件大小
          public void update(long pBytesRead, long pContentLength, int pItems) {
              String percentage = (int) (((double)pBytesRead / pContentLength) *100) +"%";
              System.out.println("总大小："+pContentLength+"，已上传："+pBytesRead +"\t" + percentage);
          }
      });
      // 处理乱码问题
      servletFileUpload.setHeaderEncoding("UTF-8");
      // 设置单个文件的最大值
      servletFileUpload.setFileSizeMax(1024*1024*10);
      //设置总文件的最大值
      servletFileUpload.setSizeMax(1024*1024*50);

      return servletFileUpload;
  }

uploadParseRequest：


private String uploadParseRequest(HttpServletRequest req,ServletFileUpload servletFileUpload,String uploadPath) throws FileUploadException, IOException {
    String msg = "" ;

    //解析前端请求 将每个表单项解析并封装成FileItem对象；
    List<FileItem> fileItems  = servletFileUpload.parseRequest(req);
    for (FileItem fileItem : fileItems) {
        //判断表单项是否为上传文件
        if (fileItem.isFormField()){
            //普通文本
            String fieldName = fileItem.getFieldName();//获取字段名：表达name的属性的值
            String value = fileItem.getString("UTF-8");
            System.out.println(fieldName+":"+value);
        }else {
            // 上传文件
            // 1.处理文件
            String uploadFileName = fileItem.getName();//上传文件名
            System.out.println("the name of uploaded file:"+uploadFileName);

            if (uploadFileName == null || uploadFileName.trim().equals("")){
                continue;
            }
            String fileExtName = uploadFileName.substring(uploadFileName.lastIndexOf(".")+1);//文件后缀
            System.out.println("info about the file: [name:"+uploadFileName+"  extname:"+fileExtName+"]");

            // use uuid make it unique
            String uuidPath = UUID.randomUUID().toString();

            // 2.处理路径
            // storePath: uploadpath 目录下的 唯一目录
            String realPath = uploadPath + "/" + uuidPath;
            File realPathFile = new File(realPath);
            makeIfNotExists(realPathFile);
            // 3.文件传输
            // get inputStream
            InputStream is = fileItem.getInputStream();
            // get outputStream write into a unique dir as a file
            OutputStream outputStream = new FileOutputStream(realPathFile+"/"+uploadFileName);
            
            //make cache
            byte[] buffer = new byte[1024];

            int len;
            while ((len = is.read(buffer))>0){
                outputStream.write(buffer,0,len);
            }
            
            
            msg = "文件上传成功";

            fileItem.delete();//上传成功，清除临时文件

            //close IOStream
            outputStream.close();
            is.close();
        }
    }
   
    return msg;
}

makeIfNotExists：

private void makeIfNotExists(File file){
     if(!file.exists()){
         file.mkdir();
     }
 }

web.xml

<?xml version="1.0" encoding="UTF-8"?>
<!--把这里的约束换成最新的-->
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee
         http://xmlns.jcp.org/xml/ns/javaee/web-app_4_0.xsd"
         version="4.0">
  
  <servlet>
    <servlet-name>FileUpload</servlet-name>
    <servlet-class>xyz.yiochin.controller.FileController</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>FileUpload</servlet-name>
    <url-pattern>/upload.do</url-pattern>
  </servlet-mapping>

  <filter>
    <filter-name>characterEncoding</filter-name>
    <filter-class>xyz.yiochin.filter.EncodingFilter</filter-class>
  </filter>
  <filter-mapping>
    <filter-name>characterEncoding</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>

  <welcome-file-list>
    <welcome-file>/ddfa.jsp</welcome-file>
  </welcome-file-list>
</web-app>