ajax文件异步上传文件，后台request获取上传的文件流

一、先看后台servlet代码，使用的是

org. apache. commons. fileupload. servlet.ServletFileUpload  组件封装的文件（否则自己处理request.inputStream很麻烦）

ServletFileUpload upload = new ServletFileUpload();  
try {
List items = upload.parseRequest(request);
Iterator iter = items.iterator();  
while(iter.hasNext()){
FileItem item = (FileItem) iter.next();
if (item.isFormField()) {  
       //如果是普通表单字段  
       String name = item.getFieldName();  
        String value = item.getString();  
   } else {
    String fieldName = item.getFieldName();  
           String fileName = item.getName();  
           String contentType = item.getContentType();  
           boolean isInMemory = item.isInMemory();  
           long sizeInBytes = item.getSize(); 
           File uploadedFile = new File("E:/Downloads/upload/" + fileName);  
               try {  
                   item.write(uploadedFile);  
               } catch (Exception e) {  
                   // TODO Auto-generated catch block  
                   e.printStackTrace();  
               }  
   }

}
} catch (FileUploadException e) {
e.printStackTrace();
}

二、前台的html和js代码

0.html页面引入一个js, 些js内容见下面。

1.html页面中要加一个label 控件：选择图片。

2.在html页面的onload事件中加如下代码：

asy.init({
url : "/hbnpc/system/activity/activityUpload",//上传的路径
filename : "pic_na",//上传的字段名
target : "fileup_id",//上传按钮的id
complete : afile//回调函数
});

三、引入的js内容

/**
*文件异步上传工具
*
*/
var asy = {};
asy.init = function(args){
asy.args = args;
var id = "asy_input_file" + new Date();
var fileinput = document.createElement("input");
asy.fileinput = fileinput;
fileinput.type = "file";
fileinput.id = id;
fileinput.name = args.filename;
fileinput.onchange = asy.upload;
fileinput.style.cssText = 'position:absolute; top:-9999px; left:-9999px';
document.body.appendChild(fileinput);
var label = document.getElementById(args.target);
asy.label = label;
label.setAttribute("for",id); 
//$(label).attr("for",id); //如果要兼容ie7 放开这句
}
asy.upload = function(){
var form = document.createElement("form"); 
  asy.form = form;
      form.action = asy.args.url;
      form.method = "post";
      form.encoding = "multipart/form-data";
 form.appendChild(asy.fileinput);
var frame = document.createElement("iframe");
frame = document.body.appendChild(frame);
asy.frame = frame;
frame.src = asy.args.url;
//frame.contentWindow.document.body.appendChild(asy.form);//不兼容ie
frame.style.cssText = 'position:absolute; top:-9999px; left:-9999px';
setTimeout(function(){
frame.contentWindow.document.body.appendChild(asy.form);
frame.onload = function(){
    asy.args.complete(this.contentWindow.document.body.outerText);//textContent//不兼容ie
    asy.clear();
    }
asy.form.submit();
},100);
}
asy.clear = function(){
document.body.removeChild(asy.frame);
asy.init(asy.args);
}