NullPointerException

[sonia pandit]

I have a jsf application in which on the first page, the user is allowed to select a file. In the action of that component
the selected file is set in the request as an attribute, and the page is redirected to a servlet. In the servlet,
i do a request.getAttribute for the file name. But I am getting a npe when the servlet tries to access the filename.
Can someone tell me what I am missing. The web.xml servlet mapping does not have any attribute. I thought
the mapping was only for context params and init params.
THanks,

Sonia

[avi sinha]

please post the code of your servlet .

avi sinha

[sonia pandit]

 

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
			try {
			       response.setContentType("application/vnd.ms-excel" );
			     //  String filename = request.getParameter("filename");
			       String filename = (String)request.getAttribute("selected");
			      // String filename = "test.xls";
			       response.setHeader("Content-disposition", "inline;filename="+filename);
			      // HSSFWorkbook wb = new HSSFWorkbook();
			       InputStream inp = new FileInputStream(filename);
			       //InputStream inp = new FileInputStream("workbook.xlsx");

			       Workbook wb = (Workbook) WorkbookFactory.create(inp);
			       Sheet sheet = ( wb).getSheetAt(0);
			       
			                       
			       // create your workbook using Apache POI
			       wb.write(response.getOutputStream());
			} catch (Exception e) {
		        e.printStackTrace();
			}
	}   

[avi sinha]

please post the stacktrace too then may be we can help here.

avi sinha

[sonia pandit]

   java.lang.NullPointerException
	at java.io.FileInputStream.<init>(Unknown Source)
	at java.io.FileInputStream.<init>(Unknown Source)
	at servlets.MyExcelServlet.doGet(MyExcelServlet.java:60)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Unknown Source)
java.lang.NullPointerException
	at java.io.FileInputStream.<init>(Unknown Source)
	at java.io.FileInputStream.<init>(Unknown Source)
	at servlets.MyExcelServlet.doGet(MyExcelServlet.java:60)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
	at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
	at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
	at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
	at java.lang.Thread.run(Unknown Source)
 

maybe it has something to do with the way I am redirecting?

   

HttpServletRequest request = (HttpServletRequest) context.getExternalContext().getRequest();
			 request.setAttribute("selected",getSelected());
			 try {
				context.getExternalContext().redirect(request.getContextPath()+"/MyExcelServlet");
			} catch (IOException e) {
			 

[avi sinha]

hello sonia ,
i think i can't give you a good suggestion for this problem. just wait for sometime , perhaps somebody else will guide you about this.
my apology

avi sinha

[Bear Bibeault]

So what's on line 60?

[Srikkanth Mohanasundaram]

  String filename = (String)request.getAttribute("selected");     

Are you sure you have this attribute set before this call? If not change this to request.getParameter("selected")

Thanks,
Srikkanth

[sonia pandit]

To answer your question

What is on line 60

:
I changed my code so I am not sure what was on line 60 but I think it was:

   request.getParameter("selected"); 

Thanks,

Sonia

[Srikkanth Mohanasundaram]

Is it working now?

[sonia pandit]

no; i am not sure what you mean. if i set an attribute how can i get a parameter?

[Bear Bibeault]

Attributes and parameters have nothing whatsoever to do with one another.

A call to getParameter cannot create an NPE. Until you find out what line is causing the issue, abandon all hope of solving this.

[Srikkanth Mohanasundaram]

InputStream inp = new FileInputStream(filename);

Do you have the file in the specified path?

[avi sinha]

Srikkanth Mohanasundaram wrote:

InputStream inp = new FileInputStream(filename);

Do you have the file in the specified path?

i think unavailability of file can't lead to a NullPointerException here.

avi sinha

[Srikkanth Mohanasundaram]

Yes you are right

[sonia pandit]

I did not know where it was looking for the file, so I made the following change to the servlet code:

  protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		// TODO Auto-generated method stub
			try {
			       response.setContentType("application/vnd.ms-excel" );
			    
			       String filename = (String)request.getAttribute("selected");  
			       String path = "c://downloads//" + filename;
			       response.setHeader("Content-disposition", "inline;filename="+path);
			      // HSSFWorkbook wb = new HSSFWorkbook();
			       InputStream inp = new FileInputStream(path);
			       //InputStream inp = new FileInputStream("workbook.xlsx");

			       Workbook wb = (Workbook) WorkbookFactory.create(inp);
			       for (int k=0; k < wb.getNumberOfSheets();k++)
			       { HSSFSheet sheet = (HSSFSheet) wb.getSheetAt(k);
			          int rows = sheet.getPhysicalNumberOfRows();
			          for(int r=0; r< rows; r++) {
			        	  HSSFRow row = sheet.getRow(r);
			        	  int cells = (row != null) ? row.getPhysicalNumberOfCells() : 0;
			        	  if( row != null) {
			        		  
			        	  }
			        	  for(int c=0; c<cells; c++){
			        		 HSSFCell cell = row.getCell(c);
			        		 String value = null;
			        		 switch(cell.getCellType()){
			        		 case HSSFCell.CELL_TYPE_FORMULA:
			        			 value = "FORMULA value=" +
			        			 cell.getCellFormula();
			        			 break;
			        		 case HSSFCell.CELL_TYPE_NUMERIC :
			        			 value = "NUMERIC value=" +
			        			  cell.getNumericCellValue();
			        			 break;
			        		 case HSSFCell.CELL_TYPE_STRING :
			        			 value="STRING value="
			        				 +cell.getStringCellValue();
			        			 break;
			        		 default:
			        			 System.out.println("CELL col="
			        					      + cell.getCellNum()
			        					      + "VALUE=" +value);
			        		 
			        				 
			        		 }
			        	  }
			          }
			       }
			                       
			       // create your workbook using Apache POI
			       wb.write(response.getOutputStream());
			} catch (Exception e) {
		        e.printStackTrace();
			}
	}

	/**  

Now I get the following error: here is the stacktrace

  java.io.FileNotFoundException: c:\downloads\null (The system cannot find the file specified)
	at java.io.FileInputStream.open(Native Method)
	at java.io.FileInputStream.<init>(Unknown Source)
	at java.io.FileInputStream.<init>(Unknown Source)
	at servlets.MyExcelServlet.doGet(MyExcelServlet.java:62)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:617)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)  

">

[Srikkanth Mohanasundaram]

Yeah you have a very descriptive error trace now.

[sonia pandit]

yes, but the file is there in that location. WHere is it looking? It should be looking in
c:/downloads/

Thanks,

Sonia

[David Newton]

It *is* looking there, for a file named "null".

Is there a file named "null" there?

[sonia pandit]

Notice that the request.getAttribute("selected") is returning a null.
THat is why it is looking for a file named null.

Thanks,

Sonia