android upload pictures backstage at a null pointer exception

I first talk about the problems encountered : In the android client upload pictures backstage at a null pointer exception userImage this object is null

server segment demo:

private File userImage;
 	private String userImageContentType;
 	private String userImageFileName;
 
 	private HttpServletRequest servletRequest;
 
 	public String execute() {
 		try {
 			
 			
 			String filePath = servletRequest.getSession().getServletContext()
 					.getRealPath("/Image/img_logo/");
 			System.out.println("Server path:" + filePath);
 			File fileToCreate = new File(filePath, this.userImageFileName);
 			FileUtils.copyFile(this.userImage, fileToCreate);
 
 			
 		} catch (Exception e) {
 			e.printStackTrace();
 			addActionError(e.getMessage());
 			return INPUT;
 		}
 		return SUCCESS;
 	}
 
 	public File getUserImage() {
 		return userImage;
 	}
 
 	public void setUserImage(File userImage) {
 		this.userImage = userImage;
 	}
 
 	public String getUserImageContentType() {
 		return userImageContentType;
 	}
 
 	public void setUserImageContentType(String userImageContentType) {
 		this.userImageContentType = userImageContentType;
 	}
 
 	public String getUserImageFileName() {
 		return userImageFileName;
 	}
 
 	public void setUserImageFileName(String userImageFileName) {
 		this.userImageFileName = userImageFileName;
 	}
 
 	public void setServletRequest(HttpServletRequest servletRequest) {
 		this.servletRequest = servletRequest;
 
 	}

upload pictures using JSP server is running correctly can also see pictures uploaded to the background

android client code :

private void uploadFile() {
 		String end = "\r\n";
 		String twoHyphens = "--";
 		String boundary = "*****";
 
 		URL url = null;
 		try {
 			url = new URL(actionUrl);
 		} catch (MalformedURLException e) {
 
 			e.printStackTrace();
 		}
 		HttpURLConnection con = null;
 		try {
 			con = (HttpURLConnection) url.openConnection();
 		} catch (IOException e) {
 			// TODO Auto-generated catch block
 			e.printStackTrace();
 		}
 		/* 允许Input、Output，不使用Cache */
 		con.setDoInput(true);
 		con.setDoOutput(true);
 		con.setUseCaches(false);
 		/* 设置传送的method=POST */
 		try {
 			con.setRequestMethod("POST");
 		} catch (ProtocolException e) {
 			// TODO Auto-generated catch block
 			e.printStackTrace();
 		}
 		/* setRequestProperty */
 		con.setRequestProperty("Connection", "Keep-Alive");
 		con.setRequestProperty("Charset", "UTF-8");
 		con.setRequestProperty("Content-Type", "multipart/form-data;boundary="
 				+ boundary);
 		/* 设置DataOutputStream */
 		DataOutputStream ds;
 		try {
 			ds = new DataOutputStream(con.getOutputStream());
 			ds.writeBytes(twoHyphens + boundary + end);
 			ds.writeBytes("Content-Disposition: form-data; "
 					+ "name=\"userImage\";filename=\"" + newName + "\"" + end);
 			ds.writeBytes(end);
 			/* 取得文件的FileInputStream */
 			FileInputStream fStream = new FileInputStream(uploadFilePath);
 			/* 设置每次写入1024bytes */
 			int bufferSize = 1024;
 			byte[] buffer = new byte[bufferSize];
 			int length = -1;
 			/* 从文件读取数据至缓冲区 */
 			while ((length = fStream.read(buffer)) != -1) {
 				/* 将资料写入DataOutputStream中 */
 				ds.write(buffer, 0, length);
 			}
 			ds.writeBytes(end);
 			ds.writeBytes(twoHyphens + boundary + twoHyphens + end);
 			/* close streams */
 			fStream.close();
 			ds.flush();
 			/* 取得Response内容 */
 			InputStream is = con.getInputStream();
 			int ch;
 			StringBuffer b = new StringBuffer();
 			while ((ch = is.read()) != -1) {
 				b.append((char) ch);
 			}
 			ds.close();
 			MainActivity.this.runOnUiThread(new Runnable() {
 				@Override
 				public void run() {
 					Toast.makeText(MainActivity.this, "上传成功", Toast.LENGTH_SHORT)
 							.show();
 				}
 
 			});
 		} catch (IOException e) {
 			e.printStackTrace();
 			MainActivity.this.runOnUiThread(new Runnable() {
 				@Override
 				public void run() {
 					Toast.makeText(MainActivity.this, "上传失败", Toast.LENGTH_SHORT)
 							.show();
 				}
 
 			});
 		}
 
 		/* 将Response显示于Dialog */
 		// showDialog("上传成功"+b.toString().trim());
 		/* 关闭DataOutputStream */
 	
 
 	}

My actionURL:

private String actionUrl = "http://192.168.2.100:8888/ImportedGood/userImage.action";

I do not know is the client code issues have not done before seeking experience sharing . .
------ Solution ---------------------------------------- ----
you upload files splicing code header files it issues
------ reference -------------------- -------------------
man did not understand what you mean I'm not an example of online reference written to the output stream directly to the picture inside it