Return generated pdf using spring MVC

Question

I am using Spring MVC .I have to write a service that would take input from the request body, add the data to the pdf and returns the pdf file to the browser. The pdf document is generated using itextpdf. How can I do this using Spring MVC. I have tried using this

@RequestMapping(value="/getpdf", method=RequestMethod.POST)
public Document getPDF(HttpServletRequest request , HttpServletResponse response, 
      @RequestBody String json) throws Exception {
    response.setContentType("application/pdf");
    response.setHeader("Content-Disposition", "attachment:filename=report.pdf");
    OutputStream out = response.getOutputStream();
    Document doc = PdfUtil.showHelp(emp);
    return doc;
}

showhelp function that generates the pdf. I am just putting some random data in the pdf for time being.

public static Document showHelp(Employee emp) throws Exception {
    Document document = new Document();

    PdfWriter.getInstance(document, new FileOutputStream("C:/tmp/report.pdf"));
    document.open();
    document.add(new Paragraph("table"));
    document.add(new Paragraph(new Date().toString()));
    PdfPTable table=new PdfPTable(2);

    PdfPCell cell = new PdfPCell (new Paragraph ("table"));

    cell.setColspan (2);
    cell.setHorizontalAlignment (Element.ALIGN_CENTER);
    cell.setPadding (10.0f);
    cell.setBackgroundColor (new BaseColor (140, 221, 8));                                  

    table.addCell(cell);                                    
    ArrayList<String[]> row=new ArrayList<String[]>();
    String[] data=new String[2];
    data[0]="1";
    data[1]="2";
    String[] data1=new String[2];
    data1[0]="3";
    data1[1]="4";
    row.add(data);
    row.add(data1);

    for(int i=0;i<row.size();i++) {
      String[] cols=row.get(i);
      for(int j=0;j<cols.length;j++){
        table.addCell(cols[j]);
      }
    }

    document.add(table);
    document.close();

    return document;   
}

I am sure this is wrong. I want that pdf to be generated and save/open dialog box to be opened through the browser, so that it can be stored in the client's file system. Please help me out.

Answer 1

You were on the right track with response.getOutputStream(), but you're not using its output anywhere in your code. Essentially what you need to do is to stream the PDF file's bytes directly to the output stream and flush the response. In Spring you can do it like this:

@RequestMapping(value="/getpdf", method=RequestMethod.POST)
public ResponseEntity<byte[]> getPDF(@RequestBody String json) {
    // convert JSON to Employee 
    Employee emp = convertSomehow(json);

    // generate the file
    PdfUtil.showHelp(emp);

    // retrieve contents of "C:/tmp/report.pdf" that were written in showHelp
    byte[] contents = (...);

    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.APPLICATION_PDF);
    // Here you have to set the actual filename of your pdf
    String filename = "output.pdf";
    headers.setContentDispositionFormData(filename, filename);
    headers.setCacheControl("must-revalidate, post-check=0, pre-check=0");
    ResponseEntity<byte[]> response = new ResponseEntity<>(contents, headers, HttpStatus.OK);
    return response;
}

Notes:

• use meaningful names for your methods: naming a method that writes a PDF document showHelp is not a good idea
• reading a file into a byte[]: example here
• I'd suggest adding a random string to the temporary PDF file name inside showHelp() to avoid overwriting the file if two users send a request at the same time