How to open html attachment in new window?

Question

My application has a feature to download different types of files(pdf, xls, html)
When user clicks on the respective links, a popup with Open, Save and Cancel option will come up.
Now the problem is when the attachment is html and user clicks Open, it opens in the main window.
I want it to be opened in a new window. It works fine for all other types of attachments.
Find below by code:
os = response.getOutputStream();
response.setHeader("Content-Disposition", "attachment;filename=document"+strDocExtn);
response.setContentType(strContentType);
response.setBufferSize(4096);
response.setContentLength(bByteArray.length);
os.write(bByteArray, 0, bByteArray.length);
os.flush();
os.close();strContentType and strDocExtn is dynamic
1. For html files it will come as text/html and .htm
2. For pdf files it will come as application/pdf and .pdf
similarly for other types..
Only html is giving me headache :(

Answer 1

target="_blank" did not work.
The attachment does not open directly. In other words, i do not use href.
The link is having an onclick event, which in turns calls the struts Action class and the response is returned as an attachment.
<a href="#" onclick="javascript:openAttachment(this.value)" value="123">And the value is unique id with which I can find to file to be downloaded.
Again the file I cannot access directly. I get it as byte array, which I put it in to my response.