Create a Java File object (or equivalent) using a byte array in memory (without a physical file)

I want to create a Java File object in memory (without creating a physical file) and populate its content with a byte array.

Can this be done?

The idea is to pass it to a Spring InputStreamSource. I'm trying the method below, but it returns saying "the byte array does not contain a file name.".

MimeMessage message = mailSender.createMimeMessage();
MimeMessageHelper helper = new MimeMessageHelper(message);   
helper.setFrom("no-reply@xxx.com", "xyz");
helper.setTo(email);
helper.setText(body,true);
helper.setSubject(subject);
helper.addInline("cImage",
        new InputStreamResource(new ByteArrayInputStream(imageByteArr)));

mailSender.send(message);

From stackoverflow

• Maybe you need to use the other constructor of InputStreamResource?

• Can you paste the full stack trace? There is no such thing as an "in memory" file. Using a ByteArrayInputStream should be sufficient.

  ---

  You need to implement Resource#getFilename(). Try the following:

  helper.addInline("cImage", new ByteArrayResource(imageByteArr){
              @Override
              public String getFilename() {
                  return fileName;
              }
          });
  

  ninesided : also works perfectly with 'addAttachment'

• Have you tried changing the resource you feed to addInline()? If you wanted the resource to be in memory, I would have tried a org.springframework.core.io.ByteArrayResource.

  Update: I think you might need to use the DataSource version of the addInline() method and then use a byte array bound data source object to feed the data into the helper class. I would try the following:

  MimeMessage message = mailSender.createMimeMessage();
  MimeMessageHelper helper = new MimeMessageHelper(message);              
  helper.setFrom("no-reply@xxx.com", "xyz");
  helper.setTo(email);
  helper.setText(body,true);
  helper.setSubject(subject);
  
  // use javax.mail.util.ByteArrayDataSource
  ByteArrayDataSource imgDS = new ByteArrayDataSource( imageByteArr, "image/png");
  helper.addInline("cImage", imgDS);
  
  mailSender.send(message);
  

  Dan : You might need to use the version of addInLine() that accepts a DataSource as your second parameter. There is a javax.util.mail.ByteArrayDataSource that implements the functionality of wrapping a byte array without a physical file.

• Maybe its worth trying a different overload of the method:

  addInline(String contentId, 
            InputStreamSource inputStreamSource, 
            String contentType)
  

  I.e.:

  addInline("cImage", 
            new InputStreamSource () 
            {  
               final private InputStream src = 
                                       new ByteArrayInputStream(imageByteArr);
               public InputStream getInputStream() {return src;}
            },
            "image/jpeg"); // or whatever image type you use
  

• It is important to create the MimeMessageHelper object correctly to support attachments and inline resources.

  Example: MimeMessageHelper helper = new MimeMessageHelper(message, true, "UTF-8");

  In this example since multipart is set to true MULTIPART_MODE_MIXED_RELATED will be used and attachments and inline resouces will be supported.