Passing binary output in servlets

Question

Hi all,
I am new to struts.In Jsp i need to give three text field values
1.category
2.two date fields.
On click of submit button,it should export the csv file from db into excel sheets.
If i didnt give the input values properly and clicking the submit button will display the error msg.
But next time if i give the proper input values,then it should disappear.
but my problem is the err msg is not removing from jsp but export is working and in my console :
SEVERE: Servlet.service() for servlet action threw exception+
java.lang.IllegalStateException: Cannot forward after response has been committed*
**and in my action class:**
The following condition is to check existence of err:
if (category.length() == 0 || startdate.length() == 0
                    || enddate.length() == 0) {
               ActionMessages errors = this.getErrors(request);
               errors.add("fatal", new ActionMessage(DATE_FIELD_MISSING, ""));
               saveErrors(request, errors);
               return mapping.findForward("failure");
The following code is for export  the data:+
if (category.equals("book")) {
               String fileName = "part.csv";
               response.setContentType("application/octet-stream");
               response.setHeader("Content-Disposition", "attachment; filename=\""
                         + fileName + "\"");
               try {
                    OutputStream oStream = response.getOutputStream();
                    oStream
                              .write(" Number, Description, Revision, Dummy, Manual, Classification, Owner, Global Effective Date, Global Expiration Date, New Part\n"
                                        .getBytes());
                    for (int i = 0; i < result.size(); i++) {
                         PartDTO part = (PartDTO) result.get(i);
                         StringBuffer sbpart = new StringBuffer(part.getPartNumber());
                         sbpart.append(',');
                         sbpart.append(part.getPartDescription());
                         sbpart.append(',');
                         sbpart.append(part.getRevision());
                         sbpart.append(',');
                         sbpart.append(part.getIsDummy());
                         sbpart.append(',');
                         sbpart.append(part.getIsManual());
                         sbpart.append(',');
                         sbpart.append(part.getClassification());
                         sbpart.append(',');
                         sbpart.append(part.getOwner());
                         sbpart.append(',');
                         sbpart.append(part.getEffectiveDate());
                         sbpart.append(',');
                         sbpart.append(part.getExpirationDate());
                         sbpart.append(',');
                         sbpart.append(part.getIsNewPart());
                         sbpart.append("\n");
                         oStream.write(sbpart.toString().getBytes());
                    oStream.close();               } catch (IOException ioe) {
return mapping.findForward("success");
I think oStream.close() will return to jsp .. so the last return statement is not working..
I dont know how to do it in someother way......Plz help me.its urgent yaar......Thanks in advance....

Answer 1

It's been awhile since I've used Struts, so don't put too much stock in this answer. That said...
Generally, you should not close the response output stream, ever. The application server takes care of this, when and if the time is right.
Also, it appears that you're writing output within an action, and then forwarding to a JSP. If you want to write binary output or some other type of output for which a text-template based JSP is not appropriate, forward to a plain old servlet, and write your output there. Define the servlet as you would any other in web.xml, and dispatch to it from Struts instead of going to a JSP.
Good luck!
- Jerry Oberle