javaweb中的文件上传的一般写法(初次接触时写)

上传文件同样可以使用form表单向后端发请求，也可以使用 ajax向后端发请求
    1. 通过form表单向后端发送请求
         <form id="postForm" action="${pageContext.request.contextPath}/UploadServlet" method="post" enctype="multipart/form-data">
            <div class="bbxx wrap">
                <input type="text" id="side-profile-name" name="username" class="form-control">
                <input type="file" id="example-file-input" name="avatar">
                <button type="submit" class="btn btn-effect-ripple btn-primary">Save</button>
            </div>
        </form>         

    2. 通过ajax向后端发送请求
        1.
            $.ajax({  
                 url : "${pageContext.request.contextPath}/UploadServlet",  
                 type : "POST",  
                 data : $( '#postForm').serialize(),  
                 success : function(data) {  
                      $( '#serverResponse').html(data);  
                 },  
                 error : function(data) {  
                      $( '#serverResponse').html(data.status + " : " + data.statusText + " : " + data.responseText);  
                 }  
            });  
            
        2. 
            var form = new FormData();
            form.append("username","zxj");
            form.append("avatar",file);
            //var form = new FormData($("#postForm")[0]);
        　   $.ajax({
                url:"${pageContext.request.contextPath}/UploadServlet",
                type:"post",
                data:form,
                processData:false,
                contentType:false,
                success:function(data){
          
                    console.log(data);
                }
            });

/**
 * 上传文件的servlet
 */
public class UploadServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public ChangeProfileServlet() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    //上传文件
            try {
//              request.getParameter("");                   //创建磁盘文件工厂
                DiskFileItemFactory fileItemFactory =  new DiskFileItemFactory();
                //创建磁盘文件项
                ServletFileUpload fileUpload = new ServletFileUpload(fileItemFactory);
//              fileUpload.setHeaderEncoding("utf-8");
                fileUpload.setHeaderEncoding("UTF-8");// 解决中文文件名上传乱码.
                //解析上传项
                List<FileItem> list = fileUpload.parseRequest(request);
                Map<String,String> map = new HashMap<String,String>();
                String fileName = null;
                for (FileItem fileItem : list) {
                    if(fileItem.isFormField()){
                        //如果是表单项
                        String name = fileItem.getFieldName();
                        String string = fileItem.getString("utf-8");
                        //表单项的集合
                        map.put(name, string);
                    }else{
                        //上传项
                        fileName = fileItem.getName();
                        InputStream is = fileItem.getInputStream();
                        // 获得文件要上传的路径（后面的路径可以自定义）:
                        String path = this.getServletContext().getRealPath("/back/imgs");
                        OutputStream os = new FileOutputStream(path+"/"+fileName);//cs.jpg
                        byte[] byts = new byte[1024];
                        int len = 0;
                        while ( (len = is.read(byts)) != -1 ) {
                            os.write(byts, 0, len);
                            os.flush();
                        }
//                      IOUtils.copy(is, os);
                        is.close();
                        os.close();
                    }
                }
                
//              BeanUtils.populate();   //将实体对应的属性赋给实体（收集数据）
                if (!fileName.equals(null)&&!fileName.equals("")) {
                    //将图片路径赋给实体的某个属性                    
                }
            //将实体的数据写入到数据库
        }
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }
    
}