java - Cannot write HSSFWorkbook to ByteArray and then read it to HSSFWorkbook

Question

5i need to convert a HSSFWorkbook (Apache's POI) to an ByteArray and later to convert the ByteArray back to the HSSFWorkbook. The following TestCase illustrates my problem:

   @Test
   public void testXLSExportImport(){
      try {
         InputStream is = new FileInputStream(FILEPATH);
         HSSFWorkbook wb = new HSSFWorkbook(is);
         byte[] exported = wb.getBytes();
         HSSFWorkbook wb2 = new HSSFWorkbook(new ByteArrayInputStream(exported)); 
         //in the line above the exception is thrown
      } catch (Exception e) {
         assertTrue(false);
      }
   }

the testcase fails with the exception: java.io.IOException: Invalid header signature; read 0x0005060000100809, expected 0xE11AB1A1E011CFD0

(I am using Apaches POI 3.5-beta3)

I hope somebody can help me... how can I get it work?!

Answer 1

You're not writing the workbook correctly! You need to use the write(Outputstream) call.

As shown in the various examples on the website, your code should instead be:

     InputStream is = new FileInputStream(FILEPATH);
     HSSFWorkbook wb = new HSSFWorkbook(is);
     ByteArrayOutputStream out = new ByteArrayOutputStream();
     wb.write(out);
     HSSFWorkbook wb2 = new HSSFWorkbook(new ByteArrayInputStream(out.toByteArray())); 

Also, don't open a Workbook from a FileInputStream, if you have a File use that directly. Opening from a File uses less memory than from a Stream.