上传图片总是出现空指针异常

上传图片总是出现空指针错误
jsp 文件中的form表单
<form name="form1" method="post" action="Uinfor_UploadPicture.action" id="form1" enctype="multipart/form-data">
  <div class="right">
  <!--Step 1-->
  <div id="Step1Container">
  <div class="title"><b>更换照片</b></div>
  <div id="uploadcontainer">
  <div class="uploadtooltip">请选择新的照片文件，文件需小于2.5MB</div>
  <div class="uploaddiv"><input type="file" name="myFile" id="fuPhoto" title="选择照片" /></div>
  <div class="uploaddiv"><input type="submit" name="btnUpload" value="上 传" id="btnUpload" /></div>
  </div>
   
  </div>
  </div>
  </form>
action 文件： 
try{
imageFileName = new Date().getTime() +
fileUpload.getExtention(fileName); //310  
File imageFile = new File(ServletActionContext.getServletContext().getRealPath("text/UploadPhoto")
+"/"+imageFileName);
fileUpload.copy(myFile,imageFile);
}catch(Exception e){
e.printStackTrace();
}


FileUpload 类：：：
package thinksns.tool;

import java.io.BufferedInputStream;

import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
public class FileUpload {
  private static final int BUFFER_SIZE = 16 * 1024;
  public void copy(File src,File dst){
  try {
InputStream in = null;
OutputStream out = null;
try {
in = new BufferedInputStream(new FileInputStream(src),
BUFFER_SIZE);
out = new BufferedOutputStream(new FileOutputStream(dst),
BUFFER_SIZE);
byte[] buffer = new byte[BUFFER_SIZE];
while (in.read(buffer) > 0) {
out.write(buffer);
}
} finally {
  if(null!=in){
  in.close();
  }
if(null!=out){
out.close();
}
}
  } catch (Exception e) {
  e.printStackTrace();
  }
  }
   
  public String getExtention(String fileName){
  int pos = fileName.lastIndexOf("."); //43
  return fileName.substring(pos);
  }
}
报错：；
java.lang.NullPointerException
at thinksns.tool.FileUpload.getExtention(FileUpload.java:43)
at thinksns.action.UinforAction.UploadPicture(UinforAction.java:310)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

感觉没写错啊，就是报空指针错

[解决办法]
<input type="file" name="myFile" id="fuPhoto" title="选择照片" />你上传的文件name为myFile那么你
将 private String fileName; 改为myFileFileName