<form action="" id="imageForm" enctype="multipart/form-data" method="POST"> 
  <input type="file" name="userPhoto" id="userPhoto"> 
  <input type="button" value="上传" id="shangchuan"> 
</form> 

<script type="text/javascript" src="/UploadFiles/2021-04-02/jquery-1.6.min.js">

js文件：




//上传头像 
  $("#shangchuan").click(function(){ 
    var file = $("#userPhoto").val(); 
    if(file==""){ 
      alert("请选择上传的头像"); 
      return; 
    } 
    else{ 
      //判断上传的文件的格式是否正确 
      var fileType = file.substring(file.lastIndexOf(".")+1); 
      if(fileType!="png"&&fileType!="jpg"){ 
        alert("上传文件格式错误"); 
        return; 
      } 
      else{ 
        var url = "/symh/user/uploadPhoto_uploadPhoto.action"+new Date().getTime(); 
        $.ajaxFileUpload({ 
          url:url, 
          secureuri:false, 
          fileElementId:"userPhoto",    //file的id 
            dataType:"text",         //返回数据类型为文本 
          success:function(data,status){ 
            if(data=="1"){ 
              alert("请上传宽度大于200像素和高度大于200像素的图片"); 
            } 
            else if(data=="2"){ 
              alert("请上传宽高比不超过2的图片"); 
            } 
            else if(data=="3"){ 
              alert("请上传文件大小不大于2M的图片"); 
            }   
            else{ 
              $("#uploadImage").hide(); 
              $("#srcImg").attr("src",data); 
              $("#previewImg").attr("src",data); 
              $("#cutImage").show(); 
              $("#bigImage").val(data); 
              cutImage();     //截取头像 
            } 
          } 
        }) 
      } 
    } 
  }) 



后台处理程序：UploadPhotoAction.Java




public class UploadPhotoAction { 
  private File userPhoto; 
  private String userPhotoContentType; 
  private String userPhotoFileName; 
 
  public File getUserPhoto() { 
    return userPhoto; 
  } 
 
  public void setUserPhoto(File userPhoto) { 
    this.userPhoto = userPhoto; 
  } 
 
  public String getUserPhotoContentType() { 
    return userPhotoContentType; 
  } 
 
  public void setUserPhotoContentType(String userPhotoContentType) { 
    this.userPhotoContentType = userPhotoContentType; 
  } 
 
  public String getUserPhotoFileName() { 
    return userPhotoFileName; 
  } 
 
  public void setUserPhotoFileName(String userPhotoFileName) { 
    this.userPhotoFileName = userPhotoFileName; 
  } 
 
  /** 
   * 用户上传图像 
   */ 
  public void uploadPhoto(){ 
    try { 
      HttpServletResponse response = (HttpServletResponse) ActionContext.getContext().get(ServletActionContext.HTTP_RESPONSE); 
      response.setCharacterEncoding("UTF-8"); 
       
      FileInputStream fis1 = new FileInputStream(getUserPhoto());     //保存文件 
      FileInputStream fis2 = new FileInputStream(getUserPhoto());    //判断文件 
      int i = this.checkImage(fis2); 
      if(i==1){ 
        response.getWriter().print("1"); 
      } 
      else if(i==2){ 
        response.getWriter().print("2"); 
      } 
      else if(i==3){ 
        response.getWriter().print("3"); 
      } 
      else {  //文件正确、上传 
        //得到文件名 
        String photoName = getPhotoName(getUserPhotoFileName()); 
         
        FileOutputStream fos = new FileOutputStream(getSavePath()+"\\"+photoName); 
        byte[] buffer = new byte[1024];  
        int len = 0;  
        while ((len = fis1.read(buffer))>0) {  
          fos.write(buffer,0,len);    
        }  
        //处理文件路径,便于在前台显示 
        String imagPathString = dealPath(getSavePath()+"\\"+photoName); 
        response.getWriter().print(imagPathString); 
         
      } 
    }  
    catch (IOException e) { 
      e.printStackTrace(); 
    } 
   
  } 
   
  /** 
   * 重新命名头像名称:用户编号+头像后缀 
   */ 
  public String getPhotoName(String photoName){ 
    //获取用户 
    HttpServletRequest request = (HttpServletRequest) ActionContext.getContext().get(ServletActionContext.HTTP_REQUEST); 
    UserBean userBean = (UserBean) request.getSession().getAttribute("userBean"); 
     
    //获取文件的后缀 
    String[] strings = photoName.split("\\."); 
    String hz = strings[1]; 
     
    //构建文件名 
    String fileName = userBean.getUserId()+"."+hz; 
    return fileName; 
  } 
   
  /** 
   * 获取上传路径 
   */ 
  public String getSavePath(){ 
    return ServletActionContext.getServletContext().getRealPath("upload/photos"); 
  } 
   
  /** 
   * 判断上传的头像是否合法 
   * 规则：宽度和高度大于200、宽高比小于2、大小小于2M 
   * 宽度或者高度<200 返回1 
   * 宽高比>2 返回2 
   * 大小大于2M 返回 3 
   * 正确 返回 0 
   */ 
  public int checkImage(FileInputStream fis){ 
    try { 
      BufferedImage image = ImageIO.read(fis); 
      double width = image.getWidth(); 
      double height = image.getHeight(); 
      if(width<200||height<200){ 
        return 1; 
      } 
      else if(width/height>2){ 
        return 2; 
      } 
      else if(fis.available()/(1024*1024)>2){ 
        return 3; 
      } 
      else { 
        return 0; 
      } 
    } catch (IOException e) { 
      e.printStackTrace(); 
    } 
    return 1; 
  } 
   
  /** 
   * 处理头像路径 
   */ 
  public String dealPath(String path){ 
    String[] strings = path.split("\\\\"); 
    String string2 = "/"; 
    for (int i = strings.length-4; i < strings.length; i++) { 
      if(i==strings.length-1){ 
        string2 = string2+strings[i]; 
      } 
      else { 
        string2 = string2+strings[i]+"/"; 
      } 
         
    } 
    return string2; 
  } 
} 



这里就介绍使用ajaxFileUpload异步上传文件。下面将介绍如何截取头像(类似于QQ上传头像)
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。