Hi,
I use the Include tag quiet extensively in the
app I am building in order to "componentise" the pages. My app is
initially going to run on a virtual Linux server which has very little memory
so I am always concerned about optimising resources use where I can. I
was a bit worried about the implementation of the IncludeTag which always
caches its output in memory buffers. With a heavily componentised page
(hierarchical) I could end up with many copies of the same jsp output in
memory before the response is complete.
I believe from previous discussions that the only
reason the IncludeTag caches the output is so that both getOutputStream and
getWriter may be called from the included page. As far as I can tell
this usually should not happen as you would only use an OutputStream if you
were writing binary data. However, the spec states that either should be
able to be called and some implementations may use either.
I have altered the current IncludeTag which was
ported from WW1 to NOT buffer output. It wraps the Response and merely
writes directly to the JspWriter like so:
class
PageResponse extends HttpServletResponseWrapper
{
...
public PrintWriter getWriter() throws
IOException
{
return new
PrintWriter(_context.getOut());
}
public
ServletOutputStream getOutputStream() throws IOException
{
throw
new
UnsupportedOperationException("Can't do
this!");
}
...
}
This works great in Tomcat but will not work on servers which
use getOutputStream(). I am looking at implementing a wrapper that
implements OutputStream but writes to the JspWriter. The problem is in
implementing the method write(int b) as some charsets use more than one
byte to represent a char. This seems to be the reason that the
current implementation buffers the entire output and then
uses:
out.write(
new
String(bytes, encoding));
However, it would be possible to only buffer enough of the output in order
to convert a few bytes into a char which can then be written to the
JspWriter.
My current quick fix works great for me and reduces the memory overhead of
my web app. I can make a Jira issue with the code if anyone is
interested.
Feed back on the writer wrapper idea?
John.
