Struts2中图片以base64方式上传至数据库

<div> 
<span id="uploadImg" style="margin:50px;background-color:#ddd;display:inline-block;height:130px;width:200px;"> 
<span style="color:#bbb;font-weight:600;border:2px #ccc dashed;font-size:20px;text-align:center;display:inline-block;height:50px;width:50px;line-height:50px;position:absolute;margin-top:40px;margin-left:75px;z-index:99">+
</span> 
<img id="preview" style="display: none; ">
</span>
<input type="file" style="display:none" name="ImgCard" id="imgFileBtn" id="imgFileBtn" style="width:150px;" onchange="javascript:setImagePreview();"/> </div> 

private File ImgCard;
private String ImgCardContentType;
private String ImgCardFileName; 
public void getImg(){
BASE64Encoder encoder = new BASE64Encoder(); 
BufferedImage bi;
boolean isImage = false; 
String[] imgExts = {".jpg", ".jpeg",".bmp", ".png"}; 
for(String ext : imgExts) { 
if(ImgCardFileName.toLowerCase().endsWith(ext)) { 
isImage = true; 
break; 
} 
} 
if((ImgCard.length()/1024/1024)>3){
return ERROR;
}
bi = ImageIO.read(ImgCard); 
ByteArrayOutputStream baos = new ByteArrayOutputStream(); 
ImageIO.write(bi, "jpg", baos); 
byte[] bytes = baos.toByteArray(); 
String img= encoder.encodeBuffer(bytes).trim(); 
}